JP2016021072A - Light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element having a new structure utilizing a photoluminescent material.SOLUTION: The light-emitting element comprises: a photoluminescence layer 110 receiving excitation light and emitting light the wavelength of which is λa in the air; a substrate 140 supporting the photoluminescence layer 110; a low heat conduction layer 109 positioned between the photoluminescence layer 110 and the substrate 104, and having thermal conductivity smaller than that of the photoluminescence layer; and a surface structure 120 positioned on at least one surface of the photoluminescence layer 110, the low heat conduction layer 109 and the substrate 104, and including at least one of a plurality of convex parts and a plurality of concave parts. The surface structure 120 restricts an angle of beam spread of the light which is emitted by the photoluminescence layer and the wavelength of which is λin the air.SELECTED DRAWING: Figure 35

Description

  The present disclosure relates to a light emitting device, and more particularly, to a light emitting device having a photoluminescence layer.

  Optical devices such as lighting fixtures, displays, and projectors are required to emit light in a necessary direction in many applications. Photoluminescent materials used in fluorescent lamps, white LEDs and the like emit isotropically. Therefore, such a material is used together with optical components such as a reflector and a lens in order to emit light only in a specific direction. For example, Patent Document 1 discloses an illumination system that secures directivity using a light distribution plate and an auxiliary reflector.

JP 2010-231941 A

  In an optical device, when optical components such as a reflector and a lens are arranged, it is necessary to increase the size of the optical device itself in order to secure the space. It is desirable to eliminate these optical components or to reduce the size as much as possible.

  The present disclosure provides a light emitting device having a novel structure using a photoluminescent material.

A light emitting device according to an embodiment of the present disclosure includes a photoluminescence layer that emits light having a wavelength of λa in the air upon receiving excitation light, a substrate that supports the photoluminescence layer, the photoluminescence layer, and the substrate. A low thermal conductivity layer having a thermal conductivity smaller than that of the photoluminescence layer, and located on at least one surface of the photoluminescence layer, the low thermal conductivity layer, and the substrate, and a plurality of convex portions and A surface structure including at least one of a plurality of recesses, and the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer.

  The generic or specific aspects described above may be implemented by elements, devices, systems, methods, or any combination thereof.

  According to an embodiment of the present disclosure, it is possible to provide a light emitting device having a novel structure using a photoluminescent material.

It is a perspective view which shows the structure of the light emitting element by a certain embodiment. It is a fragmentary sectional view of the light emitting element shown to FIG. 1A. It is a perspective view which shows the structure of the light emitting element by other embodiment. It is a fragmentary sectional view of the light emitting element shown to FIG. 1C. It is a figure which shows the result of having calculated the increase | augmentation intensity | strength of the light radiate | emitted in a front direction, changing the light emission wavelength and the height of a periodic structure, respectively. It is the graph which illustrated the conditions of m = 1 and m = 3 in Formula (10). It is a figure which shows the result of having calculated the increase | augmentation intensity | strength of the light output to a front direction by changing the light emission wavelength and the thickness t of a photo-luminescence layer. It is a figure which shows the result of having calculated the electric field distribution of the mode guided to x direction when thickness t = 238 nm. It is a figure which shows the result of having calculated the electric field distribution of the mode guided to x direction when thickness t = 539 nm. It is a figure which shows the result of having calculated the electric field distribution of the mode guided to x direction when thickness t = 300nm. It is a figure which shows the result of having calculated the light increase intensity | strength about the case where the polarization of light is a TE mode which has an electric field component perpendicular | vertical to ay direction on the same conditions as the calculation of FIG. It is a top view which shows the example of a two-dimensional periodic structure. It is a figure which shows the result of having performed the calculation similar to FIG. 2 regarding the two-dimensional periodic structure. It is a figure which shows the result of having calculated the intensification of the light which changes the light emission wavelength and the refractive index of a periodic structure, and outputs it to a front direction. It is a figure which shows the result at the time of setting the film thickness of a photo-luminescence layer to 1000 nm on the conditions similar to FIG. It is a figure which shows the result of having calculated the increase | augmentation intensity | strength of the light which changes the light emission wavelength and the height of a periodic structure, and outputs it to a front direction. It is a figure which shows the calculation result when the refractive index of a periodic structure is set to _np = 2.0 on the conditions similar to FIG. It is a figure which shows the result of having performed the calculation similar to the calculation shown in FIG. 9, assuming that the polarization of light is a TE mode having an electric field component perpendicular to the y direction. It is a figure which shows the result at the time of changing the refractive index _nwav of a photo-luminescence layer to 1.5 on the conditions similar to the calculation shown in FIG. It is a figure which shows the calculation result at the time of providing the photo-luminescence layer and periodic structure of the same conditions as the calculation shown in FIG. 2 on the transparent substrate whose refractive index is 1.5. It is a graph which illustrated the conditions of Formula (15). It is a figure which shows the structural example of the light-emitting device 200 provided with the light emitting element 100 shown to FIG. 1A and 1B and the light source 180 which makes excitation light inject into the photo-luminescence layer 110. FIG. It is a diagram showing a one-dimensional periodic structure having the x direction of the period p _x. x-direction period p _x, illustrates a two-dimensional periodic structure having a period p _y in the y direction. It is a figure which shows the wavelength dependence of the light absorption factor in the structure of FIG. 17A. It is a figure which shows the wavelength dependence of the light absorption factor in the structure of FIG. 17B. It is a figure which shows an example of a two-dimensional periodic structure. It is a figure which shows the other example of a two-dimensional periodic structure. It is a figure which shows the modification which formed the periodic structure on the transparent substrate. It is a figure which shows the other modification which formed the periodic structure on the transparent substrate. FIG. 19B is a diagram illustrating a result of calculating the enhancement of light output in the front direction by changing the emission wavelength and the period of the periodic structure in the configuration of FIG. 19A. It is a figure which shows the structure which mixed several powdery light emitting element. It is a top view which shows the example which arranged the several periodic structure from which a period differs on the photo-luminescence layer in two dimensions. It is a figure which shows an example of the light emitting element which has the structure where the several photo-luminescence layer 110 in which the uneven structure was formed on the surface was laminated | stacked. FIG. 6 is a cross-sectional view illustrating a configuration example in which a protective layer 150 is provided between a photoluminescence layer 110 and a periodic structure 120. It is a figure which shows the example which formed the periodic structure 120 by processing only a part of photo-luminescence layer 110. FIG. It is a figure which shows the cross-sectional TEM image of the photo-luminescence layer formed on the glass substrate which has a periodic structure. It is a graph which shows the result of having measured the spectrum of the front direction of the emitted light of the light emitting element made as an experiment. FIG. 4 is a diagram showing a situation where a light emitting element that emits TM mode linearly polarized light is rotated about an axis parallel to the line direction of the one-dimensional periodic structure 120 as a rotation axis. It is a graph which shows the result of having measured the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 27A. It is a graph which shows the result of having calculated the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 27A. FIG. 4 is a diagram showing a situation where a light emitting element that emits TE mode linearly polarized light is rotated about an axis parallel to the line direction of the one-dimensional periodic structure 120 as a rotation axis. It is a graph which shows the result of having measured the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 27D. It is a graph which shows the result of having calculated the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 27D. FIG. 4 is a diagram showing a situation where a light emitting element that emits TE mode linearly polarized light is rotated about an axis perpendicular to the line direction of the one-dimensional periodic structure 120 as a rotation axis. It is a graph which shows the result of having measured the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 28A. It is a graph which shows the result of having calculated the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 28A. FIG. 4 is a diagram showing a situation where a light emitting element that emits TM mode linearly polarized light is rotated about an axis parallel to the line direction of the one-dimensional periodic structure 120 as a rotation axis. It is a graph which shows the result of having measured the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 28D. It is a graph which shows the result of having calculated the angle dependence of the emitted light when rotating the prototype light emitting element as shown to FIG. 28D. It is a graph which shows the result of having measured the angle dependence of the emitted light (wavelength 610nm) of the light emitting element made as an experiment. It is a perspective view which shows typically an example of a slab type | mold waveguide. It is a schematic diagram for explaining the relationship between the wavelength of light that receives the light emission enhancement effect and the emission direction in a light emitting device having a periodic structure 120 on the photoluminescence layer. It is a typical top view which shows the example of the structure which arranged the several periodic structure from which the wavelength which shows the light emission enhancing effect differs. It is a typical top view which shows the example of the structure which arranged the some periodic structure from which the direction where the convex part of a one-dimensional periodic structure extends differs. It is a typical top view showing an example of composition which arranged a plurality of two-dimensional periodic structures. It is typical sectional drawing of a light emitting element provided with a micro lens. It is typical sectional drawing of the light emitting element which has several photo-luminescence layer from which light emission wavelengths differ. It is typical sectional drawing of the other light emitting element which has several photo-luminescence layer from which light emission wavelength differs. It is typical sectional drawing of the light emitting element which has a low heat conductive layer. It is typical sectional drawing of the other light emitting element which has a low heat conductive layer. It is typical sectional drawing of the other light emitting element which has a low heat conductive layer. It is typical sectional drawing of the other light emitting element which has a low heat conductive layer. It is typical sectional drawing of the other light emitting element which has a low heat conductive layer. It is typical sectional drawing which shows the structure of the sample used for the thermal analysis. It is a figure which shows the relationship between the thickness of a low heat conductive layer, surface temperature, and boundary temperature in case heat_generation | fever in a photo-luminescence layer is 31.4mW. It is a figure which shows the relationship between the thickness of a low heat conductive layer, surface temperature, and boundary temperature in case the heat_generation | fever in a photo-luminescence layer is 341 mW. It is typical sectional drawing which shows an example of the surface structure which has at least one of a some convex part and a some recessed part.

[1. Outline of Embodiment of Present Disclosure]
The present disclosure includes light-emitting elements described in the following items.
[Item 1]
A photoluminescence layer that receives excitation light and emits light having a wavelength of λa in the air;
A substrate supporting the photoluminescence layer;
A low thermal conductive layer located between the photoluminescent layer and the substrate and having a lower thermal conductivity than the photoluminescent layer;
A surface structure located on at least one surface of the photoluminescence layer, the low thermal conductivity layer and the substrate, and including at least one of a plurality of convex portions and a plurality of concave portions;
With
The light emitting device, wherein the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer.
[Item 2]
The light emitting device according to item 1, wherein the surface structure is located on the surface of the photoluminescence layer.
[Item 3]
A photoluminescence layer that receives excitation light and emits light having a wavelength of λa in the air;
A substrate supporting the photoluminescence layer;
A low thermal conductive layer located between the photoluminescent layer and the substrate and having a lower thermal conductivity than the photoluminescent layer;
A translucent layer provided in the photoluminescence layer and having a higher refractive index than the photoluminescence layer;
A surface structure formed on the surface of the light-transmitting layer and including at least one of a plurality of convex portions and a plurality of concave portions;
With
The light emitting device, wherein the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer.
[Item 4]
4. The light emitting device according to any one of items 1 to 3, further comprising a barrier layer positioned between the photoluminescence layer and the substrate.
[Item 5]
The light emitting device according to any one of items 1 to 4, wherein the low thermal conductivity layer has a glass transition point higher than that of the substrate.
[Item 6]
Item 7. The light emitting device according to Item 6, wherein the glass transition point of the substrate is 600 ° C or lower.
[Item 7]
The light emitting device according to any one of items 1 to 6, wherein the low thermal conductivity layer has a glass transition point higher than that of the substrate.
[Item 8]
8. The light emitting device according to any one of items 1 to 7, wherein the low thermal conductivity layer includes silicon oxide.
[Item 9]
9. The light emitting device according to any one of items 1 to 8, wherein the low thermal conductivity layer has a thermal expansion coefficient with a value between the photoluminescence layer and the substrate.
[Item 10]
The light emitting element according to any one of items 1 to 4, wherein the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer to less than 15 °.
[Item 11]
The surface structure forms a pseudo-waveguide mode inside the photoluminescence layer that maximizes the intensity of the light emitted from the photoluminescence layer in a first direction predetermined by the surface structure. 10. A light emitting device according to any one of items 1 to 9.
[Item 12]
If the distance between two adjacent convex portions or two adjacent concave portions in the surface structure is D _int and the refractive index of the photoluminescence layer with respect to the first light is n _wav-a , λ _a / n _10. The light emitting device according to any one of items 1 to 9, wherein _a relationship of _wav-a < _Dint <λa is established.
[Item 13]
The surface structure has at least one periodic structure;
The refractive index of the photoluminescence layer with respect to the light of _a wavelength in the air is lambda and n _wav-a, wherein when the period of at least one periodic structure and _{p a, λ a / n wav} -a <p a < λ relationship _a holds, the light-emitting device as described in any one of 1 to 9.

A light emitting device according to an embodiment of the present disclosure includes a photoluminescence layer that receives the excitation light and emits light having _a wavelength of λa in the air, a translucent layer disposed in proximity to the photoluminescence layer, and the photoluminescence layer. A surface structure formed on at least one surface of the luminescent layer and the light-transmitting layer and including at least one of a plurality of convex portions and a plurality of concave portions, wherein the surface structure emits the light emitted by the photoluminescent layer. Limit the directivity angle. The wavelength λ _a is, for example, in the wavelength range of visible light (for example, 380 nm to 780 nm). In applications that use infrared, the wavelength λ _a may exceed 780 nm. On the other hand, in applications using ultraviolet light, the wavelength λ _a may be less than 380 nm. In this disclosure, electromagnetic waves in general including infrared rays and ultraviolet rays are expressed as “light” for convenience.

  The photoluminescent layer includes a photoluminescent material. The photoluminescent material means a material that emits light upon receiving excitation light. The photoluminescent material includes a fluorescent material and a phosphorescent material in a narrow sense, includes not only an inorganic material but also an organic material (for example, a dye), and further includes a quantum dot (that is, a semiconductor fine particle). The photoluminescent layer may include a matrix material (ie, host material) in addition to the photoluminescent material. The matrix material is, for example, an inorganic material such as glass or oxide, or a resin.

  The light-transmitting layer disposed in the vicinity of the photoluminescence layer is formed of a material having a high transmittance with respect to light emitted from the photoluminescence layer, for example, an inorganic material or a resin. The light transmitting layer can be formed of, for example, a dielectric (particularly, an insulator that absorbs little light). The light transmissive layer may be, for example, a substrate that supports the photoluminescence layer. When the air-side surface of the photoluminescence layer has a submicron structure, the air layer can be a light-transmitting layer.

  A surface structure including at least one of a plurality of convex portions and a plurality of concave portions is formed on at least one surface of the photoluminescence layer and the light transmitting layer. Here, the “surface” means a portion in contact with another substance (that is, an interface). When the light-transmitting layer is a gas layer such as air, the interface between the gas layer and another substance (for example, a photoluminescence layer) is the surface of the light-transmitting layer. This surface structure can also be referred to as an “uneven structure”. The surface structure typically includes a portion in which a plurality of convex portions or a plurality of concave portions are periodically arranged in one or two dimensions. Such a surface structure can be referred to as a “periodic structure”. The plurality of convex portions and the plurality of concave portions are formed at the boundary between two members (or media) having different refractive indexes that are in contact with each other. Therefore, it can be said that the “periodic structure” includes a portion in which the refractive index periodically varies in a certain direction. Here, the term “periodic” is not limited to an aspect that is strictly periodic, but includes an aspect that can be said to be approximately periodic. In this specification, among a plurality of continuous convex portions or concave portions, a distance between two adjacent centers (hereinafter sometimes referred to as “center interval”) is any two adjacent convex portions or concave portions. Is also considered to be a periodic structure having a period p when it falls within a range of ± 15% of a certain value p.

  In the present specification, the “convex portion” means a raised portion with respect to a reference height portion. The “recessed portion” means a recessed portion with respect to a reference height portion. Depending on the shape, size, and distribution of the convex and concave portions, it may not be easy to determine which is the convex portion and which is the concave portion. For example, in the cross-sectional view shown in FIG. 42, it can be interpreted that the member 610 has a concave portion and the member 620 has a convex portion, and vice versa. Whatever the interpretation, it can be said that each of the member 610 and the member 620 has at least one of a plurality of convex portions and concave portions.

The distance between the centers of two adjacent convex portions or two adjacent concave portions in the surface structure (period p in the periodic structure) is typically shorter than the wavelength λ _a of the light emitted from the photoluminescence layer in the air. . When the light emitted from the photoluminescence layer is visible light, short-wavelength near infrared light, or ultraviolet light, the distance is shorter than the order of micrometers (that is, the order of microns). Therefore, such a surface structure may be referred to as a “submicron structure”. A “submicron structure” may include a portion having a central interval or period exceeding 1 micrometer (μm) in part. In the following description, a photoluminescence layer that emits visible light is mainly assumed, and the term “submicron structure” is mainly used as a term meaning a surface structure. However, the following discussion holds true for the surface structure having a fine structure exceeding the sub-micron order (for example, a fine structure of the micron order used in applications using infrared rays).

  In the light emitting device according to the embodiment of the present disclosure, a unique electric field distribution is formed inside the photoluminescence layer and the light transmitting layer, as will be described in detail later with reference to calculation results and experimental results. This is formed by the guided light interacting with the submicron structure (ie, the surface structure). The mode of light forming such an electric field distribution can be expressed as a “pseudo-waveguide mode”. By utilizing this pseudo waveguide mode, as described below, it is possible to obtain the effects of increased photoluminescence emission efficiency, improved directivity, and polarization selectivity. In the following description, the term pseudo-waveguide mode may be used to describe a new configuration and / or a new mechanism found by the present inventors. The description is merely one illustrative description and should not limit the present disclosure in any way.

The submicron structure includes, for example, a plurality of convex portions, and can satisfy the relationship of λ _a / n _wav−a <D _int <λ _a where D _int is the distance between the centers of adjacent convex portions. The submicron structure may include a plurality of concave portions instead of the plurality of convex portions. Hereinafter, for the sake of simplicity, the submicron structure will be described as having a plurality of convex portions. λ represents the wavelength of light, and λ _a represents the wavelength of light in the air. n _wav is the refractive index of the photoluminescence layer. When the photoluminescence layer is a medium in which a plurality of materials are mixed, the average refractive index obtained by weighting the refractive index of each material by the respective volume ratio is _defined as n _wav . Since generally the refractive index n depends on the wavelength, that is a refractive index to light of lambda _a it is desirable to express the n _wav-a, may be omitted for simplicity. n _wav is basically the refractive index of the photoluminescence layer. When the refractive index of the layer adjacent to the photoluminescence layer is larger than the refractive index of the photoluminescence layer, the refractive index and the photoluminescence of the layer having the larger refractive index are used. Let n _{wav be the} average refractive index obtained by weighting the refractive indices of the layers by their respective volume ratios. This is because this is optically equivalent to the case where the photoluminescence layer is composed of a plurality of layers of different materials.

When the effective refractive index of the medium with respect to the light in the pseudo waveguide mode is n _eff , n _a <n _eff <n _wav is satisfied. Here, n _a is the refractive index of air. Considering that the light in the quasi-waveguide mode propagates while totally reflecting inside the photoluminescence layer at the incident angle θ, the effective refractive index n _eff can be written as n _eff = n _wav sin θ. Further, since the effective refractive index n _eff is determined by the refractive index of the medium existing in the region where the electric field of the pseudo waveguide mode is distributed, for example, when the submicron structure is formed in the light transmitting layer, the photoluminescence layer It depends not only on the refractive index but also on the refractive index of the translucent layer. In addition, since the electric field distribution varies depending on the polarization direction of the pseudo waveguide mode (TE mode and TM mode), the effective refractive index n _eff may be different between the TE mode and the TM mode.

The submicron structure is formed in at least one of the photoluminescence layer and the light transmission layer. When the photoluminescence layer and the light transmission layer are in contact with each other, a submicron structure may be formed at the interface between the photoluminescence layer and the light transmission layer. At this time, the photoluminescence layer and the translucent layer have a submicron structure. The photoluminescent layer may not have a submicron structure. At this time, the light-transmitting layer having a submicron structure is disposed in the vicinity of the photoluminescence layer. Here, the phrase “the light-transmitting layer (or its submicron structure) is close to the photoluminescence layer” typically means that the distance between them is not more than half the wavelength λ _a . As a result, the electric field of the waveguide mode reaches the submicron structure, and the pseudo waveguide mode is formed. However, when the refractive index of the light-transmitting layer is larger than the refractive index of the photoluminescent layer, the light reaches the light-transmitting layer even if the above relationship is not satisfied. Therefore, the submicron structure of the light-transmitting layer and the photoluminescent layer the distance between the may be more than half of the wavelength lambda _a. In this specification, when the photoluminescence layer and the light-transmitting layer are in a positional relationship such that the electric field of the guided mode reaches a submicron structure and a pseudo-guided mode is formed, the two are associated with each other. Sometimes expressed.

As described above, when the submicron structure satisfies the relationship of λ _a / n _wav-a <D _int <λ _a , the submicron structure is characterized by a size on the order of submicron in applications using visible light. The submicron structure may include at least one periodic structure, for example, in the light emitting device of the embodiment described in detail below. At least one of the periodic structure, when the period as _{p a, λ a / n wav} -a <p a <λ relationship _a holds. That is, the sub-micron structures, the distance D _int between adjacent convex portions may comprise constant of the periodic structure in the p _a. When the submicron structure includes such a periodic structure, the light in the pseudo waveguide mode is diffracted by the submicron structure by repeating the interaction with the periodic structure while propagating. This is different from the phenomenon in which light propagating in free space is diffracted by the periodic structure, and is a phenomenon in which light acts on the periodic structure while being guided (that is, repeating total reflection). Therefore, even if the phase shift due to the periodic structure is small (that is, the height of the periodic structure is small), light can be efficiently diffracted.

If the mechanism as described above is used, the luminous efficiency of photoluminescence increases due to the effect of the electric field being enhanced by the pseudo waveguide mode, and the generated light is coupled to the pseudo waveguide mode. The light of the quasi-waveguide mode is bent at a traveling angle by a diffraction angle defined by the periodic structure. By utilizing this, light of a specific wavelength can be emitted in a specific direction. That is, the directivity is remarkably improved as compared with the case where no periodic structure is present. Further, since the effective refractive index n _eff (= n _wav sin θ) is different between the TE mode and the TM mode, high polarization selectivity can be obtained at the same time. For example, as shown in an experimental example later, it is possible to obtain a light emitting element that emits linearly polarized light (for example, TM mode) having a specific wavelength (for example, 610 nm) strongly in the front direction. At this time, the directivity angle of the light emitted in the front direction is, for example, less than 15 °. Here, “directivity angle” is defined as an angle between the direction in which the intensity is maximum and the direction in which the intensity is 50% of the maximum intensity with respect to the linearly polarized light having a specific wavelength to be emitted. That is, the directivity angle is an angle on one side when the direction in which the intensity is maximum is 0 °. Thus, the periodic structure (that is, the surface structure) in the embodiment of the present disclosure limits the directivity angle of light of a specific wavelength. In other words, the distribution of light of the wavelength lambda _a, to narrow angle as compared to when there is no periodic structure. Such a light distribution in which the directivity angle is reduced as compared with the case where there is no periodic structure may be referred to as “narrow angle light distribution”. The periodic structure in the embodiment of the present disclosure limits the directivity angle of light having the wavelength λa, but does not emit all light having the wavelength λa at a narrow angle. For example, in the example shown in FIG. 29 described later, light having a wavelength λa is slightly emitted in a direction away from the direction in which the intensity is maximum (for example, 20 ° to 70 °). However, as a whole, the outgoing light of wavelength λa is concentrated in the range of 0 ° to 20 °, and the directivity angle is limited.

Note that the periodic structure in the exemplary embodiment of the present disclosure has a period shorter than the wavelength λ _{a of} light, unlike a general diffraction grating. A general diffraction grating has a period sufficiently longer than the wavelength λ _{a of} light, and as a result, a specific wavelength of light is diffracted into a plurality of diffracted lights such as zero-order light (that is, transmitted light) and ± first-order diffracted light. The light is emitted separately. In such a diffraction grating, high-order diffracted light is generated on both sides of zero-order light. High-order diffracted light generated on both sides of zero-order light in the diffraction grating makes it difficult to realize narrow-angle light distribution. In other words, the conventional diffraction grating does not have an effect peculiar to the embodiment of the present disclosure in which the directivity angle of light is limited to a predetermined angle (for example, about 15 °). In this regard, the periodic structure according to the embodiment of the present disclosure has properties that are significantly different from those of conventional diffraction gratings.

  When the periodicity of the submicron structure is lowered, the directivity, light emission efficiency, polarization degree, and wavelength selectivity are weakened. What is necessary is just to adjust the periodicity of a submicron structure as needed. The periodic structure may be a one-dimensional periodic structure with high polarization selectivity or a two-dimensional periodic structure capable of reducing the degree of polarization.

  The submicron structure can include a plurality of periodic structures. The plurality of periodic structures have different periods (pitch), for example. Alternatively, the plurality of periodic structures are different from each other in the direction (axis) having periodicity, for example. The plurality of periodic structures may be formed in the same plane or may be stacked. Of course, the light-emitting element has a plurality of photoluminescence layers and a plurality of light-transmitting layers, and these may have a plurality of submicron structures.

The submicron structure can be used not only to control the light emitted from the photoluminescence layer, but also to efficiently guide the excitation light to the photoluminescence layer. That is, the excitation light is diffracted by the submicron structure and coupled to the pseudo-waveguide mode in which the excitation light is guided through the photoluminescence layer and the light transmission layer, so that the photoluminescence layer can be efficiently excited. Λ _ex / n _wav-ex <D _int <λ _ex , where λ _ex is the wavelength of light in the air that excites the photoluminescent material, and n _wav-ex is the refractive index of the photoluminescence layer for this excitation light. A sub-micron structure in which is satisfied may be used. n _wav-ex is the refractive index at the excitation wavelength of the photoluminescent material. If the period is p _ex , a submicron structure having a periodic structure in which the relationship of λ _ex / n _wav-ex <p _ex <λ _ex may be used. The wavelength λ _{ex of the} excitation light is, for example, 450 nm, but may be shorter than visible light. When the wavelength of the excitation light is within the range of visible light, the excitation light may be emitted together with the light emitted from the photoluminescence layer.

[2. Knowledge underlying this disclosure]
Before describing specific embodiments of the present disclosure, first, knowledge that is the basis of the present disclosure will be described. As described above, photoluminescent materials used in fluorescent lamps, white LEDs, and the like emit light isotropically. In order to illuminate a specific direction with light, optical components such as a reflector and a lens are required. However, if the photoluminescence layer itself emits light with directivity, the optical component as described above becomes unnecessary (or can be reduced). Thereby, the magnitude | size of an optical device or an instrument can be reduced significantly. Based on such an idea, the present inventors have studied in detail the configuration of the photoluminescence layer in order to obtain directional light emission.

The inventors of the present invention first considered that the light emission itself has a specific directionality so that light from the photoluminescence layer is biased in a specific direction. The light emission rate Γ, which is an index characterizing light emission, is expressed by the following formula (1) according to Fermi's golden rule.

In equation (1), r is a position vector, λ is the wavelength of light, d is a dipole vector, E is an electric field vector, and ρ is a density of states. In many materials except some crystalline materials, the dipole vector d has a random orientation. Further, when the size and thickness of the photoluminescence layer are sufficiently larger than the wavelength of light, the magnitude of the electric field E is almost constant regardless of the direction. Therefore, in most cases, the value of <(d · E (r))> ² does not depend on the direction. That is, the light emission rate Γ is constant regardless of the direction. For this reason, in most cases, the photoluminescence layer emits isotropically.

  On the other hand, in order to obtain anisotropic light emission from the formula (1), it is necessary to devise either a dipole vector d aligned in a specific direction or a component in a specific direction of the electric field vector to be enhanced. is there. Directional emission can be realized by any one of these devices. In an embodiment of the present disclosure, a pseudo waveguide mode in which an electric field component in a specific direction is enhanced due to the effect of confining light in the photoluminescence layer is used. The structure for that purpose is examined and the result analyzed in detail is demonstrated below.

[3. Configuration to strengthen only the electric field in a specific direction]
The inventors of the present application considered controlling light emission by using a waveguide mode with a strong electric field. When the waveguide structure itself includes a photoluminescence material, the generated light can be coupled to the waveguide mode. However, if the waveguide structure is simply formed using a photoluminescence material, the emitted light becomes a waveguide mode, so that almost no light is emitted in the front direction. Therefore, the inventors of the present application considered combining a waveguide including a photoluminescent material with a periodic structure. When the periodic structure is close to the waveguide and the light is guided while overlapping the periodic structure, a pseudo waveguide mode exists due to the action of the periodic structure. That is, this pseudo waveguide mode is a waveguide mode limited by the periodic structure, and is characterized in that the antinodes of the electric field amplitude are generated in the same period as the period of the periodic structure. This mode is a mode in which the electric field in a specific direction is strengthened by confining light in the waveguide structure. Furthermore, since this mode interacts with the periodic structure and is converted into propagating light in a specific direction by the diffraction effect, light can be emitted to the outside of the waveguide. Furthermore, since the light other than the pseudo waveguide mode has a small effect of being confined in the waveguide, the electric field is not enhanced. Therefore, most of the light emission is coupled to the pseudo waveguide mode having a large electric field component.

  In other words, the inventors of the present application configure a waveguide provided with a periodic structure close to it by a photoluminescence layer containing a photoluminescence material (or a waveguide layer having a photoluminescence layer), and thereby generating generated light. We considered to realize a directional light source by coupling to a quasi-guided mode that is converted into propagating light in a specific direction.

  As a simple structure of the waveguide structure, attention was paid to a slab type waveguide. The slab type waveguide is a waveguide in which a light guiding portion has a flat plate structure. FIG. 30 is a perspective view schematically showing an example of the slab waveguide 110S. When the refractive index of the waveguide 110S is higher than the refractive index of the transparent substrate 140 that supports the waveguide 110S, there is a mode of light propagating in the waveguide 110S. By constructing such a slab-type waveguide including a photoluminescence layer, the electric field of light generated from the light emitting point greatly overlaps the electric field of the waveguide mode, so that most of the light generated in the photoluminescence layer is guided. Can be coupled to wave mode. Furthermore, by setting the thickness of the photoluminescence layer to be approximately the wavelength of light, it is possible to create a situation in which only a waveguide mode having a large electric field amplitude exists.

  Further, when the periodic structure is close to the photoluminescence layer, the pseudo-waveguide mode is formed by the electric field of the waveguide mode interacting with the periodic structure. Even when the photoluminescence layer is composed of a plurality of layers, if the electric field of the waveguide mode reaches the periodic structure, a pseudo waveguide mode is formed. It is not necessary for all of the photoluminescence layer to be a photoluminescence material, and it is sufficient that at least a part of the photoluminescence layer has a function of emitting light.

  When the periodic structure is formed of a metal, a mode based on the waveguide mode and the effect of plasmon resonance is formed. This mode has different properties from the quasi-guided mode described above. In addition, in this mode, since the absorption by the metal is large, the loss becomes large and the effect of enhancing the light emission becomes small. Therefore, it is desirable to use a dielectric material with low absorption as the periodic structure.

First, the present inventors form a periodic structure on the surface of such a waveguide to couple the generated light to a pseudo-waveguide mode that can be emitted as propagating light in a specific angular direction. It was investigated. FIG. 1A is a perspective view schematically showing an example of a light emitting device 100 having such a waveguide (for example, a photoluminescence layer) 110 and a periodic structure (for example, a part of a light transmitting layer) 120. Hereinafter, when the light transmitting layer has a periodic structure (that is, when a periodic submicron structure is formed in the light transmitting layer), the periodic structure 120 may be referred to as the light transmitting layer 120. In this example, the periodic structure 120 is a one-dimensional periodic structure in which a plurality of stripe-shaped convex portions each extending in the y direction are arranged at equal intervals in the x direction. FIG. 1B is a cross-sectional view of the light emitting device 100 taken along a plane parallel to the xz plane. When the periodic structure 120 having a period p is provided so as to be in contact with the waveguide 110, the pseudo-waveguide mode having the wave number k _wav in the in-plane direction is converted into propagating light outside the waveguide, and the wave number k _out is It can be represented by Formula (2).

  M in Formula (2) is an integer and represents the order of diffraction.

Here, for the sake of simplicity, it is assumed that the light guided in the waveguide approximately is a light beam propagating at an angle θ _wav , and the following equations (3) and (4) hold.

In these equations, λ ₀ is the wavelength of light in the air, n _wav is the refractive index of the waveguide, n _out is the refractive index of the medium on the exit side, and θ _out is the light emitted to the substrate or air outside the waveguide. Is the exit angle. From the equations (2) to (4), the emission angle θ _out can be expressed by the following equation (5).

From equation (5), it can be seen that when n _wav sin θ _wav = mλ ₀ / p holds, θ _out = 0, and light can be emitted in a direction perpendicular to the plane of the waveguide (ie, the front).

  Based on the above principle, the generated light is coupled to a specific quasi-waveguide mode, and further converted into light having a specific emission angle using a periodic structure, thereby emitting strong light in that direction. It is considered possible.

In order to realize the above situation, there are some constraints. First, in order for the pseudo waveguide mode to exist, it is necessary that the light propagating in the waveguide is totally reflected. The condition for this is expressed by the following formula (6).

In order to diffract this pseudo waveguide mode by the periodic structure and to emit light outside the waveguide, it is necessary to satisfy −1 <sin θ _out <1 in the equation (5). Therefore, it is necessary to satisfy the following formula (7).

  On the other hand, considering the equation (6), it can be seen that the following equation (8) should be satisfied.

Further, in order to make the direction of the light emitted from the waveguide 110 the front direction (θ _out = 0), it can be seen from the equation (5) that the following equation (9) is necessary.

From formula (9) and formula (6), it can be seen that the necessary condition is the following formula (10).

When the periodic structure as shown in FIGS. 1A and 1B is provided, the first-order diffracted light with m = 1 should be designed mainly because the high-order diffraction efficiency with m = 2 or higher is low. . For this reason, in the periodic structure in the present embodiment, m = 1 and the period p is determined so as to satisfy the following expression (11) obtained by modifying expression (10).

As shown in FIG. 1A and FIG. 1B, when the waveguide (photoluminescence layer) 110 is not in contact with the transparent substrate, n _out becomes the refractive index of air (about 1.0). The period p may be determined so as to satisfy 12).

On the other hand, a structure in which the photoluminescence layer 110 and the periodic structure 120 are formed on the transparent substrate 140 as illustrated in FIGS. 1C and 1D may be employed. In this case, determined from the refractive index n _s of the transparent substrate 140 is larger than the refractive index of air, the following equation was n _out = n _s in equation (11) the period p to satisfy (13) do it.

In equations (12) and (13), it is assumed that m = 1 in equation (10), but m ≧ 2 may be satisfied. That is, when both surfaces of the light emitting element 100 are in contact with the air layer as shown in FIGS. 1A and 1B, the period p is set so that m is an integer of 1 or more and the following expression (14) is satisfied. It only has to be done.

Similarly, when the photoluminescence layer 110 is formed on the transparent substrate 140 as in the light emitting element 100a shown in FIGS. 1C and 1D, the period p is set so as to satisfy the following formula (15). It only has to be.

  By determining the period p of the periodic structure so as to satisfy the above inequality, light generated from the photoluminescence layer 110 can be emitted in the front direction, so that a light emitting device having directivity can be realized.

[4. Verification by calculation]
[4-1. Period, wavelength dependence]
The present inventors have verified by optical analysis whether light can be emitted in a specific direction as described above. The optical analysis was carried out by calculation using the Cybernet DiffractMOD. In these calculations, when light is vertically incident on the light emitting element from the outside, the increase or decrease in light absorption in the photoluminescence layer is calculated, thereby obtaining the enhancement of the light emitted vertically to the outside. The process in which light incident from the outside is coupled to the quasi-waveguide mode and absorbed by the photoluminescence layer is converted into propagating light that is emitted from the photoluminescence layer to the quasi-waveguide mode and exits perpendicularly to the outside. This corresponds to the calculation of the opposite process. Further, in the calculation of the electric field distribution in the pseudo waveguide mode, the electric field when light is incident from the outside was calculated in the same manner.

The film thickness of the photoluminescence layer is 1 μm, the refractive index of the photoluminescence layer is n _wav = 1.8, the height of the periodic structure is 50 nm, the refractive index of the periodic structure is 1.5, the emission wavelength and the period of the periodic structure are FIG. 2 shows the result of calculating the intensities of the light emitted in the front direction while changing each. As shown in FIG. 1A, the calculation model was calculated with a uniform one-dimensional periodic structure in the y direction, and the polarization of light was a TM mode having an electric field component parallel to the y direction. From the result of FIG. 2, it can be seen that a peak of enhancement exists at a certain combination of wavelength and period. In FIG. 2, the magnitude of the enhancement is represented by the shade of the color, and the darker (that is, black) has a larger enhancement and the lighter (that is, white) has a smaller enhancement.

  In the above calculation, the cross section of the periodic structure is assumed to be rectangular as shown in FIG. 1B. A graph illustrating the conditions of m = 1 and m = 3 in equation (10) is shown in FIG. Comparing FIG. 2 and FIG. 3, it can be seen that the peak positions in FIG. 2 exist at locations corresponding to m = 1 and m = 3. The reason why m = 1 is stronger is that the diffraction efficiency of the first-order diffracted light is higher than that of the third-order or higher-order diffracted light. The reason why the peak of m = 2 does not exist is that the diffraction efficiency in the periodic structure is low.

  In the region corresponding to each of m = 1 and m = 3 shown in FIG. 3, it can be confirmed that there are a plurality of lines in FIG. This is considered to be because there are a plurality of pseudo waveguide modes.

[4-2. Thickness dependence]
In FIG. 4, the refractive index of the photoluminescence layer is n _wav = 1.8, the period of the periodic structure is 400 nm, the height is 50 nm, the refractive index is 1.5, and the emission wavelength and the thickness t of the photoluminescence layer are changed. It is a figure which shows the result of having calculated the intensification of the light output in a front direction. It can be seen that the light intensity reaches a peak when the thickness t of the photoluminescence layer is a specific value.

  FIG. 5A and FIG. 5B show the results of calculating the electric field distribution of the mode guided in the x direction when the wavelength where the peak exists in FIG. 4 is 600 nm and the thickness is t = 238 nm and 539 nm. For comparison, FIG. 5C shows the result of the same calculation performed when t = 300 nm where no peak exists. The calculation model was assumed to be a one-dimensional periodic structure uniform in the y direction, as described above. In each figure, the black region indicates that the electric field strength is high, and the white region indicates that the electric field strength is low. In the case of t = 238 nm and 539 nm, there is a high electric field intensity distribution, whereas in the case of t = 300 nm, the electric field intensity is low overall. This is because when t = 238 nm and 539 nm, a waveguide mode exists and light is strongly confined. Furthermore, there is always a convex portion or a portion (antinode) where the electric field is strongest immediately below the convex portion, and it can be seen that the electric field correlated with the periodic structure 120 is generated. That is, it can be seen that a guided mode is obtained according to the arrangement of the periodic structure 120. Further, comparing the case of t = 238 nm with the case of t = 539 nm, it can be seen that the mode is different in the number of nodes (white portions) in the z direction by one.

[4-3. Polarization dependence]
Next, in order to confirm the polarization dependence, the light enhancement was calculated for the case where the polarization of the light is a TE mode having an electric field component perpendicular to the y direction under the same conditions as those in FIG. The result of this calculation is shown in FIG. Compared to the TM mode (FIG. 2), the peak position is slightly changed, but the peak position is within the region shown in FIG. Therefore, it was confirmed that the configuration of this embodiment is effective for both TM mode and TE mode polarization.

[4-4.2 Two-dimensional periodic structure]
Furthermore, the effect by a two-dimensional periodic structure was examined. FIG. 7A is a plan view showing a part of a two-dimensional periodic structure 120 ′ in which concave and convex portions are arranged in both the x and y directions. The black area in the figure indicates a convex portion, and the white area indicates a concave portion. In such a two-dimensional periodic structure, it is necessary to consider diffraction in both the x and y directions. Diffraction only in the x direction or only in the y direction is the same as in the one-dimensional case, but there is also diffraction in a direction having both x and y components (for example, an oblique 45 ° direction). It can be expected that different results will be obtained. FIG. 7B shows the result of calculating the light enhancement for such a two-dimensional periodic structure. The calculation conditions other than the periodic structure are the same as the conditions in FIG. As shown in FIG. 7B, in addition to the peak position in the TM mode shown in FIG. 2, a peak position that coincides with the peak position in the TE mode shown in FIG. 6 was also observed. This result shows that the TE mode is also converted and output by diffraction due to the two-dimensional periodic structure. In addition, regarding the two-dimensional periodic structure, it is necessary to consider diffraction that satisfies the first-order diffraction conditions simultaneously in both the x direction and the y direction. Such diffracted light is emitted in the direction of an angle corresponding to a period √2 times (that is, 2 ^1/2 times) the period p. Therefore, in addition to the peak in the case of the one-dimensional periodic structure, it is considered that a peak is generated for a period that is √2 times the period p. In FIG. 7B, such a peak can also be confirmed.

  The two-dimensional periodic structure is not limited to a square lattice structure having the same period in the x direction and the y direction as shown in FIG. 7A, but is a lattice structure in which hexagons and triangles are arranged as shown in FIGS. 18A and 18B. Also good. Moreover, the structure where the period of a direction differs (for example, x direction and y direction in the case of a square lattice) may be sufficient.

  As described above, in this embodiment, the characteristic pseudo-waveguide mode light formed by the periodic structure and the photoluminescence layer is selectively emitted only in the front direction using the diffraction phenomenon due to the periodic structure. I was able to confirm that it was possible. With such a configuration, light emission having directivity can be obtained by exciting the photoluminescence layer with excitation light such as ultraviolet rays or blue light.

[5. Study of periodic structure and photoluminescence layer configuration]
Next, the effect when various conditions such as the structure of the periodic structure and the photoluminescence layer and the refractive index are changed will be described.

[5-1. Refractive index of periodic structure]
First, the refractive index of the periodic structure was examined. The film thickness of the photoluminescence layer is 200 nm, the refractive index of the photoluminescence layer is n _wav = 1.8, the periodic structure is a uniform one-dimensional periodic structure in the y direction as shown in FIG. 1A, the height is 50 nm, and the period is The calculation was performed on the assumption that the light polarization was TM mode having an electric field component parallel to the y direction. FIG. 8 shows the result of calculating the enhancement of the light output in the front direction by changing the emission wavelength and the refractive index of the periodic structure. Further, FIG. 9 shows the results when the film thickness of the photoluminescence layer is 1000 nm under the same conditions.

  First, focusing on the film thickness of the photoluminescence layer, the light intensity with respect to the change in the refractive index of the periodic structure is more peak when the film thickness is 1000 nm (FIG. 9) than when the film thickness is 200 nm (FIG. 8). It can be seen that the shift of the wavelength (referred to as the peak wavelength) becomes small. This is because the pseudo-waveguide mode is more susceptible to the refractive index of the periodic structure as the film thickness of the photoluminescence layer is smaller. That is, the higher the refractive index of the periodic structure, the higher the effective refractive index, and the corresponding peak wavelength shifts to the longer wavelength side. This effect becomes more pronounced as the film thickness decreases. The effective refractive index is determined by the refractive index of the medium existing in the region where the electric field of the pseudo waveguide mode is distributed.

  Next, paying attention to the change in the peak with respect to the change in the refractive index of the periodic structure, it can be seen that the higher the refractive index, the wider the peak and the lower the intensity. This is because the higher the refractive index of the periodic structure, the higher the rate at which the light in the pseudo waveguide mode is emitted to the outside, so that the effect of confining the light decreases, that is, the Q value decreases. In order to keep the peak intensity high, a configuration in which light is appropriately emitted to the outside by using a pseudo-waveguide mode having a high light confinement effect (that is, a high Q value) may be used. In order to realize this, it is understood that it is not desirable to use a material having a refractive index that is too large compared to the refractive index of the photoluminescence layer for the periodic structure. Therefore, in order to increase the peak intensity and the Q value to some extent, the refractive index of the dielectric (that is, the translucent layer) constituting the periodic structure may be made equal to or less than the refractive index of the photoluminescence layer. The same applies when the photoluminescence layer contains a material other than the photoluminescence material.

[5-2. Periodic structure height]
Next, the height of the periodic structure was examined. The film thickness of the photoluminescence layer is 1000 nm, the refractive index of the photoluminescence layer is n _wav = 1.8, the periodic structure is a uniform one-dimensional periodic structure in the y direction as shown in FIG. 1A, and the refractive index is n _p = 1. 5. Calculation was performed assuming that the period was 400 nm and the polarization of light was TM mode having an electric field component parallel to the y direction. FIG. 10 shows the result of calculating the enhancement of the light output in the front direction by changing the emission wavelength and the height of the periodic structure. FIG. 11 shows the calculation result when the refractive index of the periodic structure is n _p = 2.0 under the same conditions. In the result shown in FIG. 10, the peak intensity and the Q value (that is, the line width of the peak) do not change at a height above a certain level, whereas in the result shown in FIG. 11, the height of the periodic structure is large. It can be seen that the peak intensity and the Q value are lowered. This is because, when the refractive index n _{wav of the} photoluminescence layer is higher than the refractive index n _{p of the} periodic structure (FIG. 10), the light is totally reflected, so that the electric field bleeds out (evanescent) in the pseudo waveguide mode. Only due to the interaction with the periodic structure. When the height of the periodic structure is sufficiently large, the influence of the interaction between the evanescent part of the electric field and the periodic structure is constant even if the height changes further. On the other hand, when the refractive index n _{wav of the} photoluminescence layer is lower than the refractive index n _{p of the} periodic structure (FIG. 11), the light reaches the surface of the periodic structure without being totally reflected, so the height of the periodic structure The larger the is, the more affected. As can be seen from FIG. 11, it is sufficient that the height is about 100 nm, and the peak intensity and the Q value are lowered in the region exceeding 150 nm. Therefore, when the refractive index n _{wav of the} photoluminescence layer is lower than the refractive index n _p of the periodic structure, the height of the periodic structure may be set to 150 nm or less in order to increase the peak intensity and the Q value to some extent. .

[5-3. Polarization direction]
Next, the polarization direction was examined. FIG. 12 shows the result of calculation assuming that the polarization of light is a TE mode having an electric field component perpendicular to the y direction under the same conditions as those shown in FIG. In the TE mode, the electric field of the quasi-guided mode is larger than that in the TM mode, so that it is easily affected by the periodic structure. Therefore, in the region where the refractive index n _p of the periodic structure is larger than the refractive index n _{wav of the} photoluminescence layer, the peak intensity and the Q value are significantly decreased as compared with the TM mode.

[5-4. Refractive index of photoluminescence layer]
Next, the refractive index of the photoluminescence layer was examined. FIG. 13 shows the result when the refractive index n _wav of the photoluminescence layer is changed to 1.5 under the same conditions as the calculation shown in FIG. It can be seen that the same effect as in FIG. 9 is obtained even when the refractive index n _{wav of the} photoluminescence layer is 1.5. However, it can be seen that light having a wavelength of 600 nm or more is not emitted in the front direction. This is because λ ₀ <n _wav × p / m = 1.5 × 400 nm / 1 = 600 nm from Equation (10).

  From the above analysis, if the refractive index of the periodic structure is less than or equal to the refractive index of the photoluminescence layer, or if the refractive index of the periodic structure is greater than or equal to the refractive index of the photoluminescence layer, the height should be 150 nm or less. It can be seen that the peak intensity and the Q value can be increased.

[6. Modified example]
Hereinafter, modifications of the present embodiment will be described.

[6-1. Configuration with substrate]
As described above, the light-emitting element may have a structure in which the photoluminescence layer 110 and the periodic structure 120 are formed on the transparent substrate 140 as illustrated in FIGS. 1C and 1D. In order to manufacture such a light-emitting element 100a, first, a thin film is formed on a transparent substrate 140 with a photoluminescent material (including a matrix material, if necessary, the same applies below) constituting the photoluminescent layer 110, A method of forming the periodic structure 120 thereon can be considered. In such a configuration, in order for the photoluminescence layer 110 and the periodic structure 120 to have a function of emitting light in a specific direction, the refractive index n _s of the transparent substrate 140 is less than the refractive index n _{wav of the} photoluminescence layer. It is necessary to. When the transparent substrate 140 is provided so as to be in contact with the photoluminescence layer 110, it is necessary to set the period p so as to satisfy the equation (15) where the refractive index n _out of the emission medium in the equation (10) is n _s. .

In order to confirm this, a calculation was performed when the photoluminescence layer 110 and the periodic structure 120 having the same conditions as the calculation shown in FIG. 2 were provided on the transparent substrate 140 having a refractive index of 1.5. The result of this calculation is shown in FIG. As in the result of FIG. 2, it can be confirmed that a peak of light intensity appears in a specific period for each wavelength, but it can be seen that the range of the period in which the peak appears is different from the result of FIG. In contrast, shows the condition of the expression condition of (10) was n _out = n _s equation (15) in FIG. 15. In FIG. 14, it can be seen that the peak of the light intensity appears in the region corresponding to the range shown in FIG.

  Therefore, in the light emitting element 100a in which the photoluminescence layer 110 and the periodic structure 120 are provided on the transparent substrate 140, an effect is obtained in the range of the period p that satisfies the expression (15), and the period p that satisfies the expression (13). In particular, a remarkable effect can be obtained in this range.

[6-2. Light emitting device having excitation light source]
FIG. 16 is a diagram illustrating a configuration example of a light-emitting device 200 including the light-emitting element 100 illustrated in FIGS. 1A and 1B and a light source 180 that causes excitation light to enter the photoluminescence layer 110. As described above, in the configuration of the present disclosure, light emission having directivity can be obtained by exciting the photoluminescence layer with excitation light such as ultraviolet light or blue light. By providing the light source 180 configured to emit such excitation light, the light emitting device 200 having directivity can be realized. The wavelength of the excitation light emitted from the light source 180 is typically a wavelength in the ultraviolet or blue region, but is not limited thereto, and is appropriately determined according to the photoluminescent material constituting the photoluminescent layer 110. In FIG. 16, the light source 180 is arranged so that the excitation light is incident from the lower surface of the photoluminescence layer 110. However, the present invention is not limited to such an example. For example, the excitation light is emitted from the upper surface of the photoluminescence layer 110. It may be incident. The excitation light may be incident from a direction inclined (ie, obliquely) with respect to a direction perpendicular to the main surface (ie, upper surface or lower surface) of the photoluminescence layer 110. By making the excitation light incident obliquely at an angle at which total reflection occurs in the photoluminescence layer 110, light can be emitted more efficiently.

There is also a method for efficiently emitting light by coupling excitation light into a pseudo-guide mode. 17A to 17D are diagrams for explaining such a method. In this example, the photoluminescence layer 110 and the periodic structure 120 are formed on the transparent substrate 140 as in the configuration shown in FIGS. 1C and 1D. First, as shown in FIG. 17A, the period p _x in the x direction is determined for light emission enhancement, and then, the period in the y direction is used to couple the excitation light to the pseudo waveguide mode as shown in FIG. 17B. to determine the p _y. The period p _x is determined so as to satisfy the condition in which p is replaced with p _x in Equation (10). On the other hand, in the period _py , m is an integer equal to or larger than 1, the wavelength of the excitation light is λ _ex , and the medium having the highest refractive index excluding the periodic structure 120 out of the medium in contact with the photoluminescence layer 110 is n _out. The following equation (16) is satisfied.

Here, n _out is n _s of the transparent substrate 140 in the example of FIG. 17B, but in the configuration in which the transparent substrate 140 is not provided as in FIG. 16, it is the refractive index of air (about 1.0).

In particular, if m = 1 and the period _py is determined so as to satisfy the following expression (17), the effect of converting the excitation light into the pseudo-waveguide mode can be further enhanced.

In this way, by setting the period p _y so as to satisfy the condition (in particular the condition of equation (17)) of formula (16) can be converted excitation light to the pseudo guided mode. As a result, the photoluminescence layer 110 can efficiently absorb the excitation light having the wavelength λ _ex .

FIG. 17C and FIG. 17D are diagrams showing the results of calculating the ratio of light absorption for each wavelength when light is incident on the structure shown in FIG. 17A and FIG. 17B, respectively. In this calculation, p _x = 365 nm and p _y = 265 nm, the emission wavelength λ from the photoluminescence layer 110 is about 600 nm, the wavelength λ _{ex of the} excitation light is about 450 nm, and the extinction coefficient of the photoluminescence layer 110 is 0.003. It is said. As shown in FIG. 17D, not only the light generated from the photoluminescence layer 110 but also light having a wavelength of about 450 nm that is excitation light is shown. This is because the incident light is effectively converted into the pseudo-waveguide mode, so that the proportion absorbed by the photoluminescence layer can be increased. In addition, the absorptance is increased with respect to the emission wavelength of about 600 nm. This is because if the light having a wavelength of about 600 nm is incident on this structure, the pseudo-waveguide mode can be effectively effectively applied. Is converted to. As described above, the periodic structure 120 illustrated in FIG. 17B is a two-dimensional periodic structure having structures with different periods (referred to as periodic components) in each of the x direction and the y direction. Thus, by using a two-dimensional periodic structure having a plurality of periodic components, it is possible to increase the emission intensity while increasing the excitation efficiency. In FIGS. 17A and 17B, the excitation light is incident from the substrate 140 side, but the same effect can be obtained even if it is incident from the periodic structure 120 side.

  Furthermore, as a two-dimensional periodic structure having a plurality of periodic components, a configuration as shown in FIG. 18A or 18B may be adopted. A configuration in which a plurality of convex portions or concave portions having a hexagonal planar shape are periodically arranged as shown in FIG. 18A, or a plurality of convex portions or concave portions having a triangular planar shape as shown in FIG. 18B are periodically arranged. By arranging them in a line, a plurality of main axes (in the example of the figure, axes 1 to 3) that can be regarded as periods can be determined. For this reason, a different period can be assigned to each axial direction. Each of these periods may be set to increase the directivity of light having a plurality of wavelengths, or may be set to efficiently absorb the excitation light. In any case, each cycle is set so as to satisfy the condition corresponding to the equation (10).

[6-3. Periodic structure on transparent substrate]
As shown in FIGS. 19A and 19B, the periodic structure 120a may be formed on the transparent substrate 140, and the photoluminescence layer 110 may be provided thereon. In the configuration example of FIG. 19A, the photoluminescence layer 110 is formed so as to follow the periodic structure 120 a made of unevenness on the substrate 140. As a result, a periodic structure 120b having the same period is also formed on the surface of the photoluminescence layer 110. On the other hand, in the configuration example of FIG. 19B, the surface of the photoluminescence layer 110 is processed to be flat. Also in these configuration examples, directional light emission can be realized by setting the period p of the periodic structure 120a so as to satisfy Expression (15).

In order to verify this effect, in the configuration of FIG. 19A, the intensity of light output in the front direction was calculated by changing the emission wavelength and the period of the periodic structure. Here, the film thickness of the photoluminescence layer 110 is 1000 nm, the refractive index of the photoluminescence layer 110 is n _wav = 1.8, the periodic structure 120a is a uniform one-dimensional periodic structure in the y direction, the height is 50 nm, and the refractive index is It was assumed that n _p = 1.5, the period was 400 nm, and the polarization of light was a TM mode having an electric field component parallel to the y direction. The result of this calculation is shown in FIG. 19C. Also in this calculation, a peak of light intensity was observed at a period satisfying the condition of Expression (15).

[6-4. powder]
According to the above embodiment, light emission of an arbitrary wavelength can be emphasized by adjusting the period of the periodic structure and the film thickness of the photoluminescence layer. For example, if a photoluminescent material that emits light in a wide band is used as shown in FIGS. 1A and 1B, only light of a certain wavelength can be emphasized. Therefore, the structure of the light emitting element 100 as shown in FIGS. 1A and 1B may be powdered and used as a fluorescent material. 1A and 1B may be used by being embedded in a resin or glass.

  1A and 1B, since only a specific wavelength can be emitted in a specific direction, it is difficult to realize light emission such as white having a spectrum in a wide wavelength range. Therefore, as shown in FIG. 20, by using a mixture of a plurality of powdered light emitting elements 100 having different conditions such as the period of the periodic structure and the film thickness of the photoluminescence layer, a light emitting device having a spectrum in a wide wavelength range Can be realized. In this case, the size of each light emitting element 100 in one direction is, for example, about several μm to several mm, and may include, for example, a one-dimensional or two-dimensional periodic structure of several cycles to several hundred cycles.

[6-5. Arrange structures with different periods]
FIG. 21 is a plan view showing an example in which a plurality of periodic structures having different periods are two-dimensionally arranged on the photoluminescence layer. In this example, three types of periodic structures 120a, 120b, and 120c are arranged without a gap. For example, the periodic structures 120a, 120b, and 120c have a period set so as to emit light in the red, green, and blue wavelength ranges to the front. Thus, directivity can be exhibited with respect to a spectrum in a wide wavelength region by arranging a plurality of structures with different periods on the photoluminescence layer. The configuration of the plurality of periodic structures is not limited to the above, and may be set arbitrarily.

[6-6. Laminated structure]
FIG. 22 illustrates an example of a light-emitting element having a structure in which a plurality of photoluminescence layers 110 having an uneven structure formed on the surface are stacked. A transparent substrate 140 is provided between the plurality of photoluminescence layers 110, and the concavo-convex structure formed on the surface of the photoluminescence layer 110 of each layer corresponds to the periodic structure or the submicron structure. In the example shown in FIG. 22, the three-layer periodic structures having different periods are formed, and the periods are set so as to emit light in the red, blue, and green wavelength ranges to the front. Further, the material of the photoluminescence layer 110 of each layer is selected so as to emit light of a color corresponding to the period of each periodic structure. In this way, directivity can be exhibited with respect to a spectrum in a wide wavelength range by laminating a plurality of periodic structures having different periods.

  Note that the number of layers, the structure of the photoluminescence layer 110 of each layer, and the periodic structure are not limited to those described above, and may be arbitrarily set. For example, in the structure of two layers, the first photoluminescence layer and the second photoluminescence layer are formed so as to face each other through the light-transmitting substrate, and the surface of the first and second photoluminescence layers is formed on the surface. The first and second periodic structures will be formed respectively. In this case, for each of the first photoluminescence layer and the first periodic structure pair and the second photoluminescence layer and the second periodic structure pair, the condition corresponding to the equation (15) may be satisfied. That's fine. Similarly, in the configuration of three or more layers, the condition corresponding to the formula (15) may be satisfied for the photoluminescence layer and the periodic structure in each layer. The positional relationship between the photoluminescence layer and the periodic structure may be reversed from that shown in FIG. In the example shown in FIG. 22, the period of each layer is different, but they may all be the same period. In that case, the spectrum cannot be widened, but the emission intensity can be increased.

[6-7. Configuration with protective layer]
FIG. 23 is a cross-sectional view illustrating a configuration example in which a protective layer 150 is provided between the photoluminescence layer 110 and the periodic structure 120. As described above, the protective layer 150 for protecting the photoluminescence layer 110 may be provided. However, when the refractive index of the protective layer 150 is lower than the refractive index of the photoluminescence layer 110, an electric field of light oozes out only about half the wavelength inside the protective layer 150. Therefore, when the protective layer 150 is thicker than the wavelength, light does not reach the periodic structure 120. For this reason, there is no pseudo waveguide mode, and a function of emitting light in a specific direction cannot be obtained. When the refractive index of the protective layer 150 is about the same as or higher than the refractive index of the photoluminescence layer 110, the light reaches the inside of the protective layer 150. Therefore, there is no restriction on the thickness of the protective layer 150. However, even in that case, a larger light output can be obtained by forming most of a portion where light is guided (hereinafter, this portion is referred to as a “waveguide layer”) from a photoluminescent material. Therefore, it is desirable that the protective layer 150 is thin even in this case. Note that the protective layer 150 may be formed using the same material as the periodic structure (translucent layer) 120. At this time, the light-transmitting layer having a periodic structure also serves as a protective layer. The refractive index of the light transmitting layer 120 is preferably smaller than that of the photoluminescent layer 110.

[7. material]
If the photoluminescence layer (or waveguide layer) and the periodic structure are made of a material that satisfies the above conditions, directional light emission can be realized. Any material can be used for the periodic structure. However, if the light absorptivity of the medium forming the photoluminescence layer (or waveguide layer) or the periodic structure is high, the effect of confining light is reduced, and the peak intensity and the Q value are reduced. Therefore, a medium having a relatively low light absorption can be used as a medium for forming the photoluminescence layer (or waveguide layer) and the periodic structure.

As the material of the periodic structure, for example, a dielectric having low light absorption can be used. Examples of the material of the periodic structure include, for example, MgF ₂ (magnesium fluoride), LiF (lithium fluoride), CaF ₂ (calcium fluoride), SiO ₂ (quartz), glass, resin, MgO (magnesium oxide), ITO (indium tin oxide), TiO ₂ (titanium oxide), SiN (silicon nitride), Ta ₂ O ₅ (tantalum pentoxide), ZrO ₂ (zirconia), ZnSe (zinc selenide), ZnS (zinc sulfide), etc. Can be mentioned. However, as described above, when the refractive index of the periodic structure is made lower than the refractive index of the photoluminescence layer, MgF ₂ , LiF, CaF ₂ , SiO ₂ , glass, resin having a refractive index of about 1.3 to 1.5. Can be used.

The photoluminescent material includes a fluorescent material and a phosphorescent material in a narrow sense, includes not only an inorganic material but also an organic material (for example, a dye), and further includes a quantum dot (that is, a semiconductor fine particle). In general, a fluorescent material having an inorganic material as a host tends to have a high refractive index. Examples of fluorescent materials that emit blue light include M ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ²⁺ (M = at least one selected from Ba, Sr and Ca), BaMgAl ₁₀ O ₁₇ : Eu ²⁺ , M ₃ MgSi ₂ O ₈ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca), M ₅ SiO ₄ Cl ₆ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca) Can be used. Examples of fluorescent materials that emit green light include M ₂ MgSi ₂ O ₇ : Eu ²⁺ (M = at least one selected from Ba, Sr and Ca), SrSi ₅ AlO ₂ N ₇ : Eu ²⁺ , SrSi _2. O ₂ N ₂ : Eu ²⁺ , BaAl ₂ O ₄ : Eu ²⁺ , BaZrSi ₃ O ₉ : Eu ²⁺ , M ₂ SiO ₄ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca) BaSi ₃ O ₄ N ₂ : Eu ²⁺ Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu ²⁺ , Ca ₃ SiO ₄ Cl ₂ : Eu ²⁺ , CaSi _{12-(m + n)} Al _{(m + n ) ) O n n 16-n:} Ce 3+, β-SiAlON: Eu 2+ can be used. Examples of the fluorescent material emitting red light include CaAlSiN ₃ : Eu ²⁺ , SrAlSi ₄ O ₇ : Eu ²⁺ , M ₂ Si ₅ N ₈ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca). Species), MSiN ₂ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca), MSi ₂ O ₂ N ₂ : Yb ²⁺ (at least one selected from M = Sr and Ca), Y ₂ O ₂ S: Eu ³⁺ , Sm ³⁺ , La ₂ O ₂ S: Eu ³⁺ , Sm ³⁺ , CaWO ₄ : Li ¹⁺ , Eu ³⁺ , Sm ³⁺ , M ₂ SiS ₄ : Eu ²⁺ (M = SiO, at least one selected from Ba, Sr and Ca), M ₃ SiO ₅ : Eu ²⁺ (M = at least one selected from Ba, Sr and Ca) can be used. Examples of fluorescent materials that emit yellow light include Y ₃ Al ₅ O ₁₂ : Ce ³⁺ , CaSi ₂ O ₂ N ₂ : Eu ²⁺ , Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , and CaSc ₂ O _4. : Ce ³⁺ , α-SiAlON: Eu ²⁺ , MSi ₂ O ₂ N ₂ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca), M ₇ (SiO ₃ ) ₆ Cl ₂ : Eu ²⁺ (M = at least one selected from Ba, Sr and Ca) can be used.

  For the quantum dots, for example, materials such as CdS, CdSe, core / shell CdSe / ZnS, and alloy type CdSSe / ZnS can be used, and various emission wavelengths can be obtained depending on the material. As the matrix of quantum dots, for example, glass or resin can be used.

The transparent substrate 140 shown in FIGS. 1C, 1D, and the like is made of a light-transmitting material having a refractive index lower than that of the photoluminescence layer 110. Examples of such a material include MgF ₂ (magnesium fluoride), LiF (lithium fluoride), CaF ₂ (calcium fluoride), SiO ₂ (quartz), glass, and resin. Note that it is not essential for the substrate 140 to be transparent in a configuration in which excitation light is incident on the photoluminescence layer 110 without passing through the substrate 140. The substrate 140 may be, for example, BaF ₂ , SrF ₂ , MgO, MgAl ₂ O ₄ , sapphire (Al ₂ O ₃ ), SrTiO ₃ , LaAlO ₃ , TiO ₂ , Gd ₃ Ga ₅ O ₁₂ , LaSrAlO ₄ , LaSrGaO ₄ , LaTaO. ₃ , SrO, YSZ (ZrO ₂ .Y ₂ O ₃ ), YAG, or Tb ₃ Ga ₅ O ₁₂ may be used.

[8. Production method]
Then, an example of a manufacturing method is demonstrated.

  As a method of realizing the configuration shown in FIGS. 1C and 1D, for example, a thin film of the photoluminescence layer 110 is formed on the transparent substrate 140 by a process such as vapor deposition, sputtering, and coating, and then a dielectric is formed. There is a method of forming the periodic structure 120 by patterning by a method such as photolithography. Instead of the above method, the periodic structure 120 may be formed by nanoimprinting. Further, as shown in FIG. 24, the periodic structure 120 may be formed by processing only a part of the photoluminescence layer 110. In that case, the periodic structure 120 is formed of the same material as the photoluminescence layer 110.

  The light-emitting element 100 illustrated in FIGS. 1A and 1B can be realized by, for example, manufacturing the light-emitting element 100a illustrated in FIGS. 1C and 1D and then performing a process of removing the portions of the photoluminescence layer 110 and the periodic structure 120 from the substrate 140. is there.

  In the configuration shown in FIG. 19A, for example, after the periodic structure 120a is formed on the transparent substrate 140 by a method such as a semiconductor process or nanoimprint, the material constituting the photoluminescence layer 110 is formed thereon by a method such as vapor deposition or sputtering. This is possible by doing. Alternatively, the structure shown in FIG. 19B can be realized by embedding the concave portion of the periodic structure 120a with the photoluminescence layer 110 using a method such as coating.

  In addition, said manufacturing method is an example and the light emitting element of this indication is not limited to said manufacturing method.

[9. Experimental example]
Hereinafter, an example in which a light emitting device according to an embodiment of the present disclosure is manufactured will be described.

  A sample of a light-emitting element having the same structure as that in FIG. 19A was prototyped, and the characteristics were evaluated. The light emitting element was manufactured as follows.

  A glass substrate was provided with a one-dimensional periodic structure (stripe-shaped convex portion) having a period of 400 nm and a height of 40 nm, and YAG: Ce, which is a photoluminescence material, was formed to a thickness of 210 nm thereon. FIG. 25 shows a TEM image of this cross-sectional view, and FIG. 26 shows the result of measuring the spectrum in the front direction when YAG: Ce is emitted by exciting it with a 450 nm LED. FIG. 26 shows measurement results (ref) in the absence of a periodic structure, results of measuring a TM mode having a polarization component parallel to the one-dimensional periodic structure, and a TE mode having a perpendicular polarization component. . In the case where there is a periodic structure, it can be seen that the light of a specific wavelength is remarkably increased compared to the case where there is no periodic structure. It can also be seen that the TM mode having a polarization component parallel to the one-dimensional periodic structure has a larger light enhancement effect.

  Furthermore, in the same sample, the results of measuring the angle dependency of the emitted light intensity and the calculation results are shown in FIGS. 27A to 27F and FIGS. 28A to 28F. FIG. 27A shows a state in which a light emitting element that emits TM mode linearly polarized light is rotated about an axis parallel to the line direction of the one-dimensional periodic structure 120 as a rotation axis. FIG. 27B and FIG. 27C respectively show the measurement results and calculation results for the case of rotating in this way. On the other hand, FIG. 27D shows a situation in which the light emitting element that emits TE mode linearly polarized light is rotated about an axis parallel to the line direction of the one-dimensional periodic structure 120 as a rotation axis. FIG. 27E and FIG. 27F show the measurement result and the calculation result in this case, respectively. FIG. 28A shows a state in which a light emitting element that emits TE mode linearly polarized light is rotated about an axis perpendicular to the line direction of the one-dimensional periodic structure 120 as a rotation axis. FIG. 28B and FIG. 28C show measurement results and calculation results in this case, respectively. On the other hand, FIG. 28D shows a situation where the light emitting element that emits TM mode linearly polarized light is rotated about the axis perpendicular to the line direction of the one-dimensional periodic structure 120 as the rotation axis. FIG. 28E and FIG. 28F show the measurement result and the calculation result in this case, respectively. As is clear from FIGS. 27A to 27F and FIGS. 28A to 28F, the TM mode has a higher effect of enhancement. It can also be seen that the wavelength of the enhanced light shifts with angle. For example, it can be seen that light having a wavelength of 610 nm has a high directivity and emits polarized light because the light exists only in the TM mode and in the front direction. 27B and 27C, FIG. 27E and FIG. 27F, FIG. 28B and FIG. 28C, and FIG. 28E and FIG. Supported by.

  FIG. 29 shows the angle dependence of the intensity when light having a wavelength of 610 nm is rotated about a direction perpendicular to the line direction as the rotation axis, as shown in FIG. 28D. There is a strong light emission enhancement in the front direction, and it can be seen that the light is hardly enhanced at other angles. It can be seen that the directivity angle of the light emitted in the front direction is less than 15 °. As described above, the directivity angle is an angle at which the intensity is 50% of the maximum intensity, and is represented by an angle on one side with respect to the direction of the maximum intensity. From the results shown in FIG. 29, it can be seen that directional light emission is realized. Furthermore, since all the emitted light is a TM mode component, it can be seen that polarized light emission is realized at the same time.

  The verification experiment described above was performed using YAG: Ce that emits light in a wide wavelength band. Even if an experiment is performed with a similar configuration using a photoluminescent material that emits light in a narrow band, high directivity and polarized light emission can be realized for light of that wavelength. Further, when such a photoluminescent material is used, a light source that does not generate light in other directions and in other polarization states can be realized because light of other wavelengths is not generated.

[10. Other variations]
Next, another modified example of the light emitting element and the light emitting device of the present disclosure will be described.

[10-1. Structure that reduces viewing angle dependency]
As described above, the wavelength and emission direction of light subjected to the light emission enhancement effect by the submicron structure of the light emitting element of the present disclosure depend on the configuration of the submicron structure. Consider a light-emitting element having a periodic structure 120 on a photoluminescence layer 110 shown in FIG. Here, the periodic structure 120 is formed of the same material as that of the photoluminescence layer 110, and the case where the periodic structure 120 includes the one-dimensional periodic structure 120 illustrated in FIG. 1A is illustrated. The light receiving the emission enhancement by the one-dimensional periodic structure 120 is defined as a period p (nm) of the one-dimensional periodic structure 120, a refractive index n _wav of the photoluminescence layer 110, and a refractive index n _out of an external medium from which the light is emitted, When the incident angle to the one-dimensional periodic structure 120 is θ _wav and the exit angle from the one-dimensional periodic structure 120 to the external medium is θ _out , p × n _wav × sin θ _wav −p × n _out × sin θ _out = mλ The relationship is satisfied (see the above formula (5)). Here, λ is the wavelength of light in the air, and m is an integer.

From the above equation, θ _out = arcsin [(n _wav × sin θ _wav −mλ / p) / n _out ] is obtained. Therefore, in general, when the wavelength λ is different, the emission angle θ _{out of the} light subjected to the emission enhancement is different. As a result, as schematically shown in FIG. 31, the color of the visible light differs depending on the direction of observation.

In order to reduce the viewing angle dependency, n _wav and n _out may be selected so that (n _wav × sin θ _wav −mλ / p) / n _out is constant regardless of the wavelength λ. Since the refractive index of the material has wavelength dispersion (wavelength dependence), the wavelength of n _wav and n _out such that (n _wav × sin θ _wav −mλ / p) / n _out does not depend on the wavelength λ. A material having dispersibility may be selected. For example, when the external medium is air, n _out is approximately 1.0 regardless of the wavelength. Therefore, as a material for forming the photoluminescence layer 110 and the one-dimensional periodic structure 120, a material having a small wavelength dispersion of the refractive index n _wav. It is desirable to select. Furthermore, a reverse dispersion material is preferable in which the refractive index is low for light having a shorter refractive index n _wav .

[10-2. Structure that emits white light]
Also, as shown in FIG. 32A, white light can be emitted by arranging a plurality of periodic structures having different wavelengths that exhibit a light emission enhancement effect. In the example shown in FIG. 32A, a periodic structure 120r that can enhance red light (R), a periodic structure 120g that can enhance green light (G), and a periodic structure 120b that can enhance blue light (B) are arranged in a matrix. Has been. The periodic structures 120r, 120g, and 120b are, for example, one-dimensional periodic structures, and the convex portions are arranged in parallel to each other. Therefore, the polarization characteristics are the same for all colors of red, green, and blue. By the periodic structures 120r, 120g, and 120b, the light of the three primary colors that has received light emission enhancement is emitted and mixed, resulting in white light and linearly polarized light.

  When the periodic structures 120r, 120g, and 120b arranged in a matrix are called unit periodic structures (or pixels), the size of the unit periodic structure (that is, the length of one side) is, for example, three times or more of the period. is there. In order to obtain a mixed color effect, it is desirable that the unit periodic structure is not recognized by the human eye. For example, the length of one side is preferably smaller than 1 mm. Here, although each unit periodic structure is drawn in the square, it is not restricted to this, For example, the periodic structures 120r, 120g, and 120b which adjoin each other may be shapes other than squares, such as a rectangle, a triangle, and a hexagon.

  In addition, the photoluminescence layer provided under the periodic structures 120r, 120g, and 120b may be common to the periodic structures 120r, 120g, and 120b, or different photoluminescence materials corresponding to light of the respective colors. A photoluminescence layer may be provided.

  As shown in FIG. 32B, a plurality of periodic structures (including periodic structures 120h, 120i, and 120j) having different orientations in which the convex portions of the one-dimensional periodic structure extend may be arranged. The wavelengths of light with which a plurality of periodic structures enhance light emission may be the same or different. For example, when the same periodic structure is arranged as shown in FIG. 32B, unpolarized light can be obtained. Further, when the arrangement of FIG. 32B is applied to each of the periodic structures 120r, 120g, and 120b in FIG. 32A, unpolarized white light can be obtained as a whole.

  Of course, the periodic structure is not limited to a one-dimensional periodic structure, and a plurality of two-dimensional periodic structures (including periodic structures 120k, 120m, and 120n) may be arranged as shown in FIG. 32C. At this time, as described above, the periods and orientations of the periodic structures 120k, 120m, and 120n may be the same as or different from each other, and may be set as necessary.

  As shown in FIG. 33, for example, an array of microlenses 130 may be arranged on the light emission side of the light emitting element. By using the array of microlenses 130 to bend light emitted in an oblique direction in the normal direction, a color mixing effect can be obtained.

  The light-emitting element shown in FIG. 33 has regions R1, R2, and R3 having the periodic structures 120r, 120g, and 120b in FIG. 32A, respectively. In the region R1, the red light R is emitted in the normal direction by the periodic structure 120r, for example, the green light G is emitted in an oblique direction. The green light G emitted in the oblique direction is bent in the normal direction by the refraction action of the microlens 130. As a result, in the normal direction, the red light R and the green light G are mixed and observed. Thus, by providing the microlens 130, the phenomenon that the wavelength of the emitted light differs depending on the angle is suppressed. Here, a microlens array in which a plurality of microlenses corresponding to a plurality of periodic structures are integrated is illustrated, but the present invention is not limited to this. Of course, the periodic structure to be tiled is not limited to the above example, and can be applied to the case where the same periodic structure is tiled, and can also be applied to the configuration shown in FIG. 32B or 32C.

  The optical element having an action of bending light emitted in an oblique direction may be a lenticular lens instead of the microlens array. In addition to a lens, a prism can also be used. An array of prisms may be used. You may arrange | position a prism separately corresponding to a periodic structure. The shape of the prism is not particularly limited. For example, a triangular prism or a pyramid prism can be used.

  A method for obtaining white light (or light having a wide spectral width) is not only based on the above-described periodic structure but also based on a photoluminescence layer as shown in FIGS. 34A and 34B, for example. As shown in FIG. 34A, white light can be obtained by stacking a plurality of photoluminescence layers 110b, 110g, and 110r having different emission wavelengths. The stacking order is not limited to the illustrated example. As shown in FIG. 34B, a photoluminescence layer 110y that emits yellow light may be stacked on the photoluminescence layer 110b that emits blue light. The photoluminescence layer 110y can be formed using, for example, YAG.

In addition, when using a photoluminescent material that is mixed with a matrix (host) material such as a fluorescent dye, a plurality of photoluminescent materials having different emission wavelengths are mixed with the matrix material, and a single photoluminescent layer is used. White light can be emitted. Such a photoluminescence layer capable of emitting white light can be used in the configuration in which the unit periodic structure is tiled as described with reference to FIGS. 32A, 32B, and 32C.
[10-3. Structure with low thermal conductivity layer]
In the light emitting element of the present disclosure, when the photoluminescence layer 110 is excited, heat is generated in the photoluminescence layer 110. For example, when the photoluminescence layer 110 is excited with light having a wavelength of 450 nm to obtain photoluminescence having a center wavelength of 550 nm, even if the conversion efficiency is 100%, approximately 20% is heated by Stokes loss. In principle, it is difficult to suppress this heat generation. For this reason, for example, when the intensity of the excitation light is 5 W, heat generation of about 1 W occurs.

  In the light-emitting element of the present disclosure, the substrate is one of the components that should consider heat generation in the photoluminescence layer. The substrate has a function of supporting the structure of the light-emitting element and can be formed using various materials, but the heat resistance differs depending on the material. For example, inexpensive glass substrates and resin substrates have low heat resistance, and quartz substrates have high heat resistance, but are relatively expensive. The light emitting element of the following form is provided with a low thermal conductivity layer between the photoluminescence layer and the substrate so that a substrate with low heat resistance can be used. Hereinafter, the form of a light emitting element provided with a low heat conductive layer is demonstrated.

  The light-emitting element illustrated in FIG. 35 includes a substrate 140, a low thermal conductive layer 109, a photoluminescence layer 110, and a periodic structure 120. The low thermal conductive layer 109 is located between the photoluminescence layer 110 and the substrate 140. The periodic structure 120 is located on at least one surface of the photoluminescence layer 110, the low thermal conductive layer 109, and the substrate 104. In the form shown in FIG. 35, the periodic structure 120 is located on the upper surface 110u of the photoluminescence layer 110, that is, on the side where the low thermal conductive layer 109 is not provided, and is formed integrally with the surface of the photoluminescence layer 110. ing. When the periodic structure 120 is not located in the photoluminescence layer 110, the photoluminescence layer 110 and the periodic structure 120 are close to each other according to the above-described definition.

  The low thermal conductive layer 109 has a lower thermal conductivity than the photoluminescence layer 110. For example, the thermal conductivity of the photoluminescence layer 110 is approximately 10 W / m · K. Specifically, when the photoluminescence layer 110 is formed of YAG, the thermal conductivity of the photoluminescence layer 110 is 11 to 14 W / m · K. For this reason, the low thermal conductive layer 109 has a thermal conductivity of approximately 10 W / m · K or less. Further, the low thermal conductive layer 109 has a glass transition point smaller than that of the substrate 140. The substrate 140 may have a glass transition point of 600 ° C. or lower. That is, it may be an inexpensive glass substrate having a low glass transition point.

  Specifically, the low thermal conductive layer 109 is formed of a material such as silicon oxide, zirconia, or alumina. More specifically, a silicon oxide film, zirconia, alumina or the like formed by a thin film forming technique such as sputtering or vapor deposition. The substrate 140 is made of soda glass, borosilicate glass, resin, or the like.

  As shown in FIG. 35, heat generated in the photoluminescence layer 110 for the above-described reason isotropically conducted in the photoluminescence layer 110. However, since the thermal conductivity of the low thermal conductive layer 109 is low, it is difficult to conduct from the photoluminescence layer 110 to the low thermal conductive layer 109. For this reason, the generated heat is difficult to conduct to the substrate 140 and is conducted in the photoluminescence layer 110 in a direction parallel to the photoluminescence layer 110. As a result, an increase in the temperature of the substrate 140 is suppressed.

  Substrates with low heat resistance have a high coefficient of thermal expansion when exposed to high temperatures, so the substrate breaks due to thermal shock due to rapid heating, the glass transition point is low, the substrate is altered, the substrate is deformed, Problems such as distortion in the element structure may occur. On the other hand, according to the light emitting element shown in FIG. 35, it is suppressed that the temperature of the board | substrate 140 raises as mentioned above. For this reason, generation | occurrence | production of such a subject is suppressed and it becomes possible to use an inexpensive and low heat resistant board | substrate. Thus, the manufacturing cost of the light emitting element can be reduced.

  Further, from the viewpoint of stress relaxation, the low thermal conductive layer 109 may have a thermal expansion coefficient having a value between the photoluminescence layer 110 and the substrate 104. Thereby, in addition to the suppression of the heat conduction to the substrate 104 described above, the compressive stress to the photoluminescence layer 110 caused by the thermal expansion of the inexpensive substrate 104 can be relaxed.

  The preferred thickness of the low thermal conductive layer 109 depends on the heat generated in the photoluminescence layer of the light emitting element, the material of the substrate used, and the like. However, if the low thermal conductive layer 109 is provided, a rise in the temperature of the substrate is suppressed as compared with a light-emitting element that does not have the low thermal conductive layer 109. The relationship between the thickness of the low thermal conductive layer 109 and the temperature of the substrate 140 will be exemplified in the following examples.

  In the light-emitting element, the periodic structure 120 may be provided at various positions as long as the low thermal conductive layer 109 is located between the photoluminescence layer 110 and the substrate. For example, as illustrated in FIG. 36, in the light emitting element, the periodic structure 120 a may be provided in the low thermal conductive layer 109. Specifically, the periodic structure 120 is located on the upper surface of the low thermal conductive layer 109. The upper surface 109u of the low thermal conductive layer 109 is in contact with the photoluminescence layer 110, and the upper surface 110u of the photoluminescence layer 110 has a periodic structure 120b that follows the periodic structure 120a. As shown in FIG. 37, the upper surface 110u of the photoluminescence layer 110 may be flat.

Further, the periodic structure may be provided in a component other than the substrate 140, the low thermal conductive layer 109, and the photoluminescence layer. The light-emitting element illustrated in FIG. 38 includes a substrate 140, a photoluminescence layer 110, a low thermal conductive layer 109 positioned between the photoluminescence layer 110 and the substrate, and a light-transmitting layer 125. The translucent layer 125 is provided in the photoluminescence layer 110 and has a higher refractive index than the photoluminescence layer. Specifically, the light transmissive layer 125 is in contact with the upper surface 110 u of the photoluminescence layer 110, and the periodic structure 120 is provided on the upper surface 125 u of the light transmissive layer 125. In this case, the above-described relationship is satisfied, where n _wav is an average refractive index obtained by weighting the refractive index of the light-transmitting layer 125 and the refractive index of the photoluminescence layer 110 with the respective volume ratios.

  In the case where a glass substrate with low heat resistance is used as the substrate 104, the glass substrate contains more alkali metal than the quartz substrate. Although the temperature increase of the substrate 104 during operation of the light-emitting element is suppressed by the low thermal conductive layer 109, the temperature is considerably higher than room temperature, so that alkali metal can diffuse into the photoluminescence layer. As a result, the light emission characteristics of the photoluminescence layer 110 may be deteriorated. That is, there is a possibility that the light emission intensity of the light emitting element gradually decreases due to long-time operation. In order to suppress the diffusion of the alkali metal, the light emitting element may further include a barrier layer 108 between the photoluminescence layer 110 and the substrate 104 as shown in FIG. The material constituting the barrier layer 108 can be selected according to, for example, the characteristics of the element that should prevent diffusion from the substrate 140. An oxide or nitride having strong covalent bonding can suppress diffusion with respect to various elements and can be suitably used as a barrier layer. In the form shown in FIG. 39, the periodic structure 120 is located on the upper surface 109 u of the low thermal conductive layer 109. The barrier layer 108 is provided so as to follow the periodic structure 120. According to this embodiment, since the barrier layer 108 is provided in contact with the photoluminescence layer 110, the barrier layer 108 includes not only the substrate 104 but also the low thermal conductive layer 109 including an alkali metal. Diffusion to the photoluminescence layer 110 can be suppressed.

In addition, when the low thermal conductive layer 109 does not substantially contain an alkali metal and is formed of, for example, an oxide or nitride having a strong covalent bond as described above, the low thermal conductive layer 109 is a barrier. It also functions as a layer.
For example, when the photoluminescence layer 110 is made of crystalline Ce-doped YAG, the barrier layer can be made of oxide or nitride not containing silicon. More specifically, the barrier layer can be formed of aluminum oxide, aluminum nitride, yttrium oxide, or the like.

  Hereinafter, thermal analysis was performed to confirm the amount of heat generated when the photoluminescence layer was excited and the effect of the low thermal conductive layer. For the calculation, software ANSYS made by Ansys Japan was used as a calculation tool. As shown in FIG. 40, the thickness and thermal conductivity shown in Table 1 were used as the substrate 104, the low thermal conductive layer 109, and the photoluminescence layer 110, respectively.

The circumference of the sample was calculated assuming that it is filled with a medium having a thermal conductivity of 10 Wm ⁻² K ⁻¹ assuming convection air. The size of the substrate was 2 mm × 2 mm, and a heat generation region 110 r having a diameter of 200 μm was set in the photoluminescence layer 110. As the material substantially equal to the set thermal conductivity, for example, the substrate 104 is soda glass, the low thermal conductive layer 109 is silicon oxide, and the photoluminescence layer 110 is YAG.

  The heat generation amounts in the heat generation region 110r are 31.4 mW and 341 mW, the thickness of the low thermal conductive layer 109 is changed from 1 μm to 100 μm, and the temperature on the upper surface 110 u of the photoluminescence layer 110 and the interface temperature between the substrate 104 and the low thermal conductive layer 109 are changed. Calculated.

  The results when the calorific values are 31.4 mW and 341 mW are shown in FIGS. 41A and 41B. As can be seen from FIGS. 41A and 41B, even when the thickness of the low thermal conductive layer 109 changes, the upper surface 110u of the photoluminescence layer 110, that is, the surface temperature hardly changes, and the heat generation amount is 31.4 mW and 341 mW. Are about 105 ° C. and 850 ° C., respectively. If the calorific value is 341 mW, the amount of heat generated by the photoluminescence layer 110 is considerably large, and it can be seen that the photoluminescence layer 110 is heated to a temperature much higher than 600 ° C. which is the glass transition point of an inexpensive glass substrate. .

  As shown in FIG. 41A, when the calorific value is 31.4 mW, the thickness of the low thermal conductive layer 109 is about 3 μm, and the interface temperature starts to decrease. When the thickness of the low thermal conductive layer is about 30 μm, the interface temperature is reduced to about 95 ° C.

  As shown in FIG. 41B, when the calorific value is 341 mW, the thickness of the low thermal conductive layer 109 is about 3 μm and the interface temperature starts to decrease. When the thickness of the low thermal conductive layer is about 30 μm, the interface temperature decreases to about 750 ° C.

  From these results, it was found that the heat conducted to the substrate 104 can be suppressed by providing the low thermal conductive layer 109 between the photoluminescence layer 110 and the substrate 104. It was also found that the thickness of the low thermal conductive layer 109 can be determined according to the amount of heat generated in the photoluminescence layer 110 and the heat resistance required for the substrate 104.

  The light-emitting element of the present disclosure can be applied to various optical devices such as a lighting fixture, a display, and a projector.

100, 100a Light-emitting element 110 Photoluminescence layer (waveguide layer)
108 Barrier layer 109 Low thermal conductive layer 120, 120 ′, 120a, 120b, 120c Light transmissive layer (periodic structure, submicron structure)
140 Transparent substrate 150 Protective layer 180 Light source 200 Light emitting device 500 Light source unit (light emitting device)
510 Excitation light source 520 Collimating lens 530 Reflector 540 Support body 550 Lens 560 Filter 570 Angle adjustment mechanism (rotating shaft)
580 Laser module 700 Light emitting element

Claims (13)

A photoluminescence layer that receives excitation light and emits light having a wavelength of λa in the air;
A substrate supporting the photoluminescence layer;
A low thermal conductive layer located between the photoluminescent layer and the substrate and having a lower thermal conductivity than the photoluminescent layer;
A surface structure located on at least one surface of the photoluminescence layer, the low thermal conductivity layer and the substrate, and including at least one of a plurality of convex portions and a plurality of concave portions;
With
The light emitting device, wherein the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer.   The light emitting device according to claim 1, wherein the surface structure is located on the surface of the photoluminescence layer. A photoluminescence layer that receives excitation light and emits light having a wavelength of λa in the air;
A substrate supporting the photoluminescence layer;
A low thermal conductive layer located between the photoluminescent layer and the substrate and having a lower thermal conductivity than the photoluminescent layer;
A translucent layer provided in the photoluminescence layer and having a higher refractive index than the photoluminescence layer;
A surface structure formed on the surface of the light-transmitting layer and including at least one of a plurality of convex portions and a plurality of concave portions;
With
The light emitting device, wherein the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer.   The light emitting element in any one of Claim 1 to 3 further provided with the barrier layer located between the said photo-luminescence layer and the said board | substrate.   The light emitting device according to claim 1, wherein the low thermal conductivity layer has a glass transition point higher than that of the substrate.   The light emitting device according to claim 5, wherein the glass transition point of the substrate is 600 ° C. or lower.   The light emitting device according to claim 1, wherein the low thermal conductivity layer has a glass transition point higher than that of the substrate.   The light emitting device according to claim 1, wherein the low thermal conductivity layer contains silicon oxide.   The light emitting device according to any one of claims 1 to 8, wherein the low thermal conductivity layer has a thermal expansion coefficient having a value between the photoluminescence layer and the substrate. 5. The light emitting device according to claim 1, wherein the surface structure limits a directivity angle of the light having _a wavelength λ _{a in} the air emitted from the photoluminescence layer to less than 15 °.   The surface structure forms a pseudo-waveguide mode inside the photoluminescence layer that maximizes the intensity of the light emitted from the photoluminescence layer in a first direction predetermined by the surface structure. The light emitting device according to claim 1. If the distance between two adjacent convex portions or two adjacent concave portions in the surface structure is D _int and the refractive index of the photoluminescence layer with respect to the first light is n _wav-a , λ _a / n The light emitting device according to claim 1, wherein _a relationship of _wav-a <D _int <λ _a is established. The surface structure has at least one periodic structure;
The refractive index of the photoluminescence layer with respect to the light of _a wavelength in the air is lambda and n _wav-a, wherein when the period of at least one periodic structure and _{p a, λ a / n wav} -a <p a < The light emitting device according to claim 1, wherein _a relationship of λa is established.

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