WO2018179540A1

WO2018179540A1 - Light-emitting element and light-emitting device

Info

Publication number: WO2018179540A1
Application number: PCT/JP2017/037787
Authority: WO
Inventors: 市橋　宏基; 林　克彦
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2017-03-28
Filing date: 2017-10-19
Publication date: 2018-10-04
Also published as: JP2020095065A

Abstract

A light-emitting element (10) emits fluorescence on the basis of excitation light. The light-emitting element (10) is provided with a periodic structure (5) including a plurality of phosphor layers (11) and a plurality of object layers (12). The plurality of phosphor layers (11) includes a phosphor for emitting fluorescence. The plurality of object layers (12) has a refractive index different from the refractive index of the plurality of phosphor layers (11). The plurality of phosphor layers (11) and the plurality of object layers (12) are periodically layered in alternating fashion so that a plurality of peaks in the intensity distribution of an electric field of the excitation light when the excitation light is incident on the periodic structure (5) is positioned on the plurality of object layers (12).

Description

Light emitting element and light emitting device

The present disclosure relates to a light-emitting element and a light-emitting device that emit fluorescence based on excitation light.

Non-Patent Document 1 discloses a technique using a one-dimensional photonic crystal to enhance fluorescence emission based on excitation light. The one-dimensional photonic crystal of Non-Patent Document 1 is configured by repeatedly laminating a layer containing a quantum dot phosphor and a layer made of another material, and an electric field of excitation light inside each phosphor layer. The strength is designed to be greater than another adjacent layer. Thereby, even if excitation light with small intensity | strength is used, the intensity | strength of a big fluorescence emission is obtained.

The present disclosure provides a light-emitting element and a light-emitting device that can reduce light density quenching due to irradiated excitation light in a light-emitting element that emits fluorescence.

The light-emitting element according to one embodiment of the present disclosure emits fluorescence based on excitation light. The light emitting element includes a periodic structure including a plurality of phosphor layers and a plurality of object layers. The plurality of phosphor layers include a phosphor that emits fluorescence. The plurality of object layers have a refractive index different from that of the plurality of phosphor layers. When the excitation light is incident on the periodic structure, the plurality of phosphor layers and the plurality of object layers are alternately and periodically so that the plurality of peaks of the intensity distribution of the electric field of the excitation light are located in the plurality of object layers. Are stacked.

The light emitting device according to one embodiment of the present disclosure includes an excitation light source and a light emitting element. The excitation light source irradiates the light emitting element with excitation light.

According to the light emitting element and the light emitting device according to the present disclosure, when excitation light is incident on the light emitting element, the peak position of the electric field intensity is outside the phosphor layer. Thereby, the light density quenching by the excitation light irradiated to the light emitting element can be reduced.

FIG. 1 is a diagram illustrating a configuration of a projector according to the first embodiment of the present disclosure. FIG. 2 is a diagram illustrating a configuration of the light emitting element according to the first embodiment. FIG. 3 is a diagram for explaining the function of the light emitting device according to the first embodiment. FIG. 4 is a graph for explaining the light dispersion relationship in the photonic crystal of the light-emitting element. FIG. 5 is a graph showing a simulation result of the electric field analysis regarding the light emitting element. FIG. 6 is a view for explaining a modification of the light emitting device according to the first embodiment. FIG. 7 is a diagram illustrating a configuration of a light emitting device according to another embodiment.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed descriptions of already well-known matters and repeated descriptions for substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

In addition, the applicant provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present disclosure, and is not intended to limit the claimed subject matter. .

(Embodiment 1)
In the first embodiment, a light-emitting element and a light-emitting device according to the present disclosure will be described using an application example to a projector.

[1. Constitution]
The configurations of the light emitting device and the light emitting element according to this embodiment will be described below.

[1-1. About the projector]
The light emitting device according to the present disclosure is used as a light source in a projector, for example. The configuration of the projector and the light emitting device in Embodiment 1 will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of a projector 1 in the present embodiment.

As shown in FIG. 1, the projector 1 includes a light emitting device 2, a light guide optical system 3, a DMD (digital mirror device) 49, and a projection lens 51. The projector 1 projects projection light indicating an image on a screen or the like. The light emitting device 2 emits yellow light, for example. The projector 1 further includes, for example, a blue light source (not shown) that emits blue light, and generates projection light using the yellow light from the light emitting device 2 and the blue light.

The light emitting device 2 includes an excitation light source 41, a collimating lens system 42, a dichroic mirror 43, a condensing optical system 44, and a phosphor wheel 20. The light emitting device 2 uses the phosphor wheel 20 to perform wavelength conversion from, for example, blue light excitation light to yellow light fluorescence.

In this embodiment, the excitation light source 41 emits blue light having a wavelength of 450 nm as excitation light. The excitation light source 41 is composed of, for example, a plurality of semiconductor lasers. The excitation light source 41 is not limited to a semiconductor laser, and may be composed of various light source elements such as a light emitting diode.

The collimating lens system 42 includes a plurality of lenses such as a collimating lens, and is disposed between the excitation light source 41 and the phosphor wheel 20. The collimating lens system 42 collimates light incident on the light emitting element 10.

The dichroic mirror 43 has, for example, an optical characteristic of transmitting blue light and reflecting yellow light. The dichroic mirror 43 is disposed to face the excitation light source 41 via the collimating lens system 42, the phosphor wheel 20, and the condensing optical system 44.

The condensing optical system 44 includes, for example, a plurality of optical lenses. The condensing optical system 44 is disposed such that the focal position is located on the main surface of the phosphor wheel 20. The focal position of the condensing optical system 44 may be in the vicinity of the main surface of the phosphor wheel 20.

In the light emitting device 2, the excitation light emitted from the excitation light source 41 is collimated in the collimator lens system 42 as shown in FIG. 1 and corresponds to the focal position of the condensing optical system 44 on the main surface of the phosphor wheel 20. The position is irradiated. The optical system inside the light emitting device 2 is not limited to the above configuration, and may be set as appropriate.

The phosphor wheel 20 includes a light emitting element 10 that emits fluorescence based on excitation light, a base material 21 having a main surface, and a rotating device 22 including a motor and the like. The light emitting element 10 is provided on the main surface of the substrate 21. The rotating device 22 rotationally drives the base material 21 using the main surface as a rotating surface. The phosphor wheel 20 converts the excitation light into fluorescence while rotating the light emitting element 10 on the base material 21 while cooling the light emitting element 10.

According to the light emitting element 10 according to the present embodiment, light density quenching can be reduced. Here, light density quenching means that the internal quantum efficiency in conversion from excitation light to fluorescence decreases when the light intensity of the excitation light is increased. The configuration of the light emitting element 10 will be described later.

In the present embodiment, the phosphor wheel 20 is a transmission type, and emits the converted fluorescence in the same direction as the incident direction of the excitation light. Fluorescence (yellow light) emitted from the phosphor wheel 20 is incident on the dichroic mirror 43 in a parallel state by reversing the condensing optical system 44. The light emitting device 2 reflects the yellow light after wavelength conversion by the dichroic mirror 43 and emits it to the light guide optical system 3.

The light guide optical system 3 includes a condenser lens 45, a rod integrator 46, a relay lens 47, a field lens 48, and a total reflection prism 50. The light guide optical system 3 condenses the yellow light from the light emitting device 2 on the rod integrator 46 by the condenser lens 45, and combines the yellow light and the separately supplied blue light into white light in the rod integrator 46. The synthesized white light is guided to the DMD 49 via the relay lens 47, the field lens 48 and the total reflection prism 50.

The DMD 49 spatially modulates the white light guided from the light guide optical system 3 so as to represent an image based on an external video signal, and generates projection light. The projector 1 is not limited to the DMD 49, and various spatial light modulation elements such as a liquid crystal panel may be used.

The projection lens 51 projects the projection light generated by the DMD 49 to the outside of the projector 1. Thereby, based on the projection light from the projector 1, a desired image is projected. At this time, the upper limit of the luminance of the image is defined by the light output from the light emitting device 2 or the like.

In the projector 1 as described above, there is a demand for higher brightness that increases the brightness of the projection light. In order to increase the brightness of the projector 1, it is necessary to increase the light intensity of the excitation light from the excitation light source 41 in order to increase the light output of the light emitting device 2.

In the conventional projector, when the light intensity of the excitation light is increased, there is a problem that the conversion efficiency from the excitation light to the fluorescence is lowered due to the influence of the light density quenching. Therefore, in the light emitting device 2 according to the present embodiment, the light emitting element 10 reduces light density quenching due to excitation light emitted from the excitation light source 41. Hereinafter, the configuration of the light emitting element 10 according to the present embodiment will be described.

[1-2. Configuration of light emitting element]
A configuration of the light-emitting element 10 according to Embodiment 1 will be described with reference to FIG. FIG. 2 is a diagram illustrating a configuration of the light emitting element 10 according to the present embodiment.

The light emitting device 10 according to this embodiment is configured by laminating a multilayer film on a base material 21 of a phosphor wheel 20 (see FIG. 1). FIG. 2 shows a cross-sectional structure of the light emitting element 10.

Hereinafter, the thickness direction of the light emitting element 10 is defined as an X direction, and two directions orthogonal to each other along the main surface of the light emitting element 10 are defined as a Y direction and a Z direction. The excitation light is incident from the −X side of the light emitting element 10.

As shown in FIG. 2, the light emitting element 10 includes a plurality of phosphor layers 11, a plurality of low refractive index layers 12, a substrate 16, and a dichroic filter 17.

The phosphor layer 11 includes a phosphor that is excited by incident excitation light (blue light) and emits fluorescence (yellow light). The refractive index n1 of the phosphor layer 11 is, for example, 1.8, and the thickness TH1 of the phosphor layer 11 is, for example, 75 nm.

In the present embodiment, the phosphor layer 11 is made of a nanocomposite material including the quantum dots 13 constituting the phosphor particles. The quantum dots 13 are made of, for example, CdSe, CuInS ₂ or the like. According to the phosphor layer 11 in the present embodiment, desired physical characteristics such as the refractive index n1 can be obtained by controlling the density and the like of the quantum dots 13.

The low refractive index layer 12 is made of various materials that transmit excitation light (for example, PMMA, CA resin, etc.). The refractive index n2 of the low refractive index layer 12 is, for example, 1.5, and the thickness TH2 of the low refractive index layer 12 is, for example, 72 nm. The low refractive index layer 12 may be made of a nanocomposite material. The low refractive index layer 12 is an example of an object layer in the present embodiment.

In the light emitting device 10 according to this embodiment, as shown in FIG. 2, a plurality of phosphor layers 11 and low refractive index layers 12 are alternately stacked. The plurality of stacked phosphor layers 11 and the plurality of low refractive index layers 12 constitute a photonic crystal 5. The number of phosphor layers 11 and the number of low refractive index layers 12 in the photonic crystal 5 are, for example, 10 layers or more, for example, several hundred layers.

In the light emitting device 10 according to the present embodiment, for example, a photonic crystal in which the phosphor layer 11 and the low refractive index layer 12 set to the above-described thicknesses TH1 and TH2 and refractive indexes n1 and n2 are periodically arranged. The periodic structure of 5 controls the intensity distribution of the excitation light and reduces the light density quenching. The photonic crystal 5 is an example of a periodic structure in the present embodiment. Details of the photonic crystal 5 will be described later.

The substrate 16 is, for example, a sapphire substrate. The substrate 16 may be fixed on the main surface of the base material 21 in the phosphor wheel 20 (see FIG. 1), or may be configured integrally with the base material 21.

The dichroic filter 17 is a dielectric multilayer film, and has an optical characteristic of transmitting excitation light (for example, blue light) and reflecting fluorescence (for example, yellow light). The dichroic filter 17 is provided on the surface of the substrate 16 where the excitation light is incident.

[2. Operation]
Operations of the light emitting device 2 and the light emitting element 10 according to the present embodiment will be described below.

In the light emitting device 2 according to the present embodiment (see FIG. 1), the excitation light source 41 irradiates the light emitting element 10 with excitation light. As shown in FIG. 2, the excitation light from the excitation light source 41 is incident in the + X direction from the −X side of the light emitting element 10. The excitation light is transmitted through the dichroic filter 17 in the light emitting element 10 and propagates so as to sequentially pass through the phosphor layer 11 and the low refractive index layer 12 that are stacked as the photonic crystal 5. Each time the excitation light propagates through the phosphor layer 11, it is absorbed by the phosphor quantum dots 13 and converted into fluorescence.

As shown in FIG. 2, the converted fluorescence in the light emitting element 10 includes light that is emitted from the + X side while maintaining the + X direction, and light that is reflected by the dichroic filter 17 and emitted from the + X side in the −X direction. There are two types of light. That is, the light emitting element 10 emits the converted light so as to be transmitted from the + X side based on the excitation light incident from the −X side. The light emitting device 2 outputs fluorescence (yellow light) emitted from the light emitting element 10.

[2-1. About Light Emitting Element]
The light emitting element 10 according to the present embodiment has a function of controlling the electric field distribution of the excitation light by the periodic structure of the photonic crystal 5 when the excitation light is converted into fluorescence in the light emitting device 2 as described above. The function of the light emitting element 10 will be described with reference to FIG.

FIG. 3 shows a spatial distribution of the electric field intensity distributed inside the photonic crystal 5 when the excitation light enters the light emitting element 10. Hereinafter, the excitation light is a TE wave (Transverse 波 Electric Wave) propagating in the X direction, and the vibration direction of the transverse wave component of the electric field is the Y direction. In FIG. 3, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the intensity of the Y component Ey of the electric field (that is, the light intensity of the TE wave).

When the excitation light is incident on the light emitting element 10, it is distributed as a wave having a wave number kx corresponding to the frequency of the excitation light in accordance with the light dispersion relationship defined by the periodic structure of the photonic crystal 5. At this time, as shown in FIG. 3, periodic peaks (maximum values) and valleys (minimum values) are formed in the electric field intensity distribution of the excitation light. Here, in the vicinity of the peak of the electric field intensity of the excitation light, the light intensity of the excitation light becomes larger than the surroundings, and it is considered that the influence of light density quenching is large.

Therefore, in the present embodiment, the periodic peaks of the electric field intensity Ey ² of the excitation light inside the photonic crystal 5, to be located in the low refractive index layer 12, respectively, keep constituting the photonic crystal 5. At this time, for example, periodic valleys having an electric field intensity Ey ² are located in each phosphor layer 11 (see FIG. 3).

According to the light emitting element 10 as described above, when the light emitting element 10 is irradiated with excitation light, the electric field intensity Ey ² in the phosphor layer 11 becomes lower than the peak value inside the light emitting element 10. Therefore, the light density quenching in the light emitting element 10 can be reduced rather than the light density quenching that can occur at the peak value. Thereby, when the light intensity of the excitation light output from the excitation light source 41 is increased, loss due to light density quenching can be reduced, and the conversion efficiency from excitation light to fluorescence in the light emitting device 2 can be improved.

[2-1-1. About Photonic Crystal]
Details of the photonic crystal 5 for realizing the function of the light emitting element 10 as described above will be described with reference to FIG.

FIG. 4 is a graph for explaining the light dispersion relationship in the photonic crystal 5 of the light-emitting element 10. The horizontal axis in FIG. 4 represents the wave number kx in the X direction. The vertical axis in FIG. 4 is the wavelength λ. Curves C <b> 1 and C <b> 2 indicate the light dispersion relationship in the photonic crystal 5.

In the light emitting device 10 according to the present embodiment (see FIG. 2), the light dispersion relationship is defined as follows in the photonic crystal 5 due to the periodic structure of the phosphor layer 11 and the low refractive index layer 12. Is done.

In the above formula (1), a is a parameter representing the thickness of the phosphor layer 11, b is a parameter representing the thickness of the low refractive index layer 12, and c is the speed of light (in a vacuum or in air). is there. The wave number k1x depends on the refractive index n1 of the phosphor layer 11 and the angular frequency ω of light (2π times the light frequency) as shown in the above equation (2), and the wave number k2x is as shown in the above equation (3). It depends on the refractive index n2 of the low refractive index layer 12 and the angular frequency ω of light.

Equation (1) substitutes an electromagnetic wave solution corresponding to the periodic structure of the photonic crystal 5 based on Bloch's theorem in the wave equation (Maxwell's equation) of the electromagnetic wave propagating in the X direction, and expands the dielectric constant in a Fourier series. Can be obtained.

In the photonic crystal 5, the wave number kx corresponding to the angular frequency ω of light becomes a complex number according to the equation (1), and a frequency section that does not exist as a real number, that is, a photonic band gap is generated (see FIG. 4). The photonic crystal 5 has first and second photonic bands that define the dispersion relation of light having an angular frequency ω of light outside the photonic band gap based on the formula (1).

The first photonic band associates the angular frequency ω of light below the photonic band gap with the real wave number kx in the photonic crystal 5. The second photonic band associates the angular frequency ω of light equal to or greater than the photonic band gap with the real wave number kx.

In FIG. 4, curve C1 corresponds to the first photonic band. Curve C2 corresponds to the second photonic band. In FIG. 4, since the wavelength λ (= 2πc / ω) is used for the vertical axis, the curve C1 of the first photonic band is above the curve C2 of the second photonic band.

The minimum value of the curve C1 of the first photonic band represents the photonic band edge (PBE) on the first photonic band side, that is, the band edge in the first photonic band. The maximum value of the curve C2 of the second photonic band represents the PBE on the second photonic band side, that is, the band edge in the second photonic band.

In the present embodiment, the angular frequency (or equivalently the wavelength) of the excitation light irradiated from the excitation light source 41 of the light emitting device 2 (see FIG. 1) matches the vicinity of the PBE on the second photonic band side. Next, the photonic crystal 5 is formed (see FIG. 4). The vicinity of PBE is, for example, a frequency position at which the reflectance is minimized in the frequency spectrum of the reflectance of light by the photonic crystal 5 and is within a range including a frequency position adjacent to PBE.

According to the configuration of the photonic crystal 5 described above, when excitation light is distributed inside the photonic crystal 5, the peak of the electric field intensity is located in the low refractive index layer 12 as described above (see FIG. 3). ). In such a configuration, the thickness TH1 of the phosphor layer 11 and the low refractive index layer 12 is set so that the angular frequency near the PBE based on the formula (1) matches the angular frequency of the excitation light as a reference. It is obtained by setting TH2 and refractive indexes n1 and n2. The values of the various parameters TH1, TH2, n1, and n2 can be appropriately selected from the formula (1) within the range where the above relationship is established. Further, the frequency of the excitation light used as a reference may be set as appropriate.

Further, since the angular frequency of the excitation light is in the vicinity of the position of the minimum angular frequency in the vicinity of PBE, the loss due to reflection when the excitation light is incident on the light emitting element 10 can be reduced, and the excitation light The conversion efficiency from fluorescence to fluorescence can be improved.

[2-2. About simulation]
With respect to the light emitting element 10 based on the photonic crystal 5 as described above, a simulation performed by the present inventor will be described with reference to FIG.

FIG. 5 is a graph showing the results of an electric field analysis simulation in the photonic crystal 5 of the light emitting element 10. 5, the horizontal axis, the converted distance (cT [μm]), represents using the time T and the speed of light c, the vertical axis represents the electric field intensity Ey ² in arbitrary units.

In the analysis simulation of FIG. 5, the intensity of the electric field when the excitation light (TE wave) is incident on the photonic crystal 5 of the light emitting element 10 according to the present embodiment is simulated by the FDTD (Finite-difference time-domain) method. did. At this time, the assumption that excitation light was not attenuated by fluorescence emission was used. In the simulation model of the photonic crystal 5, when the temporal change of the electric field intensity Ey ² is numerically calculated for the transmitted light, the reflected light, and the light passing through a predetermined position inside the phosphor layer 11, FIG. The result was obtained.

According to FIG. 5, the electric field intensity Ey ² of the excitation light is reduced to about 20% of the transmitted light inside the phosphor layer 11. According to the above assumption, the light incident on the simulation model of the photonic crystal 5 is transmitted without being absorbed. From this, it is considered that the transmitted light curve in FIG. 5 corresponds to the electric field intensity Ey ² generated in the conventional phosphor structure (for example, bulk structure) that does not use the periodic structure like the photonic crystal 5 in the present embodiment. It is done. Therefore, according to the photonic crystal 5 in the present embodiment, it was confirmed that the light intensity of the excitation light can be reduced in the phosphor layer 11 as compared with the conventional structure.

[3. Effect]
As described above, the light-emitting element 10 according to the present embodiment emits fluorescence based on preset excitation light. The light emitting element 10 includes a phosphor layer 11 and a low refractive index layer 12 as an object layer. The phosphor layer 11 includes phosphor quantum dots 13 that emit fluorescence. The low refractive index layer 12 has a refractive index n2 different from the refractive index n1 in the phosphor layer 11. A plurality of phosphor layers 11 and low refractive index layers 12 are alternately stacked. In the photonic crystal 5 that is a periodic structure including the phosphor layer 11 and the low refractive index layer 12 that are stacked, the peak of the electric field intensity distribution when the excitation light is incident is positioned in the low refractive index layer 12. The phosphor layer 11 and the low refractive index layer 12 are periodically arranged.

According to the above light emitting element 10, when excitation light is incident on the light emitting element 10, the peak position of the electric field intensity is outside the phosphor layer 11. Thereby, the optical density quenching by the excitation light irradiated to the light emitting element 10 can be reduced.

In this embodiment, the photonic crystal 5 has a photonic band gap, a first photonic band that defines a dispersion relationship of light having a frequency smaller than a frequency corresponding to the photonic band gap, and a photonic band gap. A second photonic band defining a dispersion relationship of light having a frequency higher than the corresponding frequency. Based on such a photonic band structure, the distribution of the electric field intensity of the excitation light can be controlled, and light density quenching can be reduced.

In this embodiment, the refractive index n2 in the low refractive index layer 12 is lower than the refractive index n1 in the phosphor layer 11. The angular frequency of the photonic band edge in the second photonic band has an angular frequency near the angular frequency of the excitation light (see FIG. 4). Specifically, the angular frequency of the photonic band edge in the second photonic band is lower than the angular frequency of the excitation light. When refractive index n2 <refractive index n1, light density quenching in the light emitting element 10 can be reduced by setting the PBE on the second photonic band side in the vicinity of the frequency of the excitation light.

In this embodiment, at least 10 layers of the phosphor layer 11 and the low refractive index layer 12 are laminated in the periodic structure. Thereby, the periodic structure functions as the photonic crystal 5 and the electric field intensity distribution can be controlled.

In this embodiment, the light emitting device 2 includes the light emitting element 10 and the excitation light source 41 that irradiates the light emitting element 10 with excitation light. The light emitting element 10 includes a photonic crystal 5. The photonic crystal 5 is a periodic structure in which a plurality of phosphor layers 11 and a plurality of low refractive index layers 12 having a refractive index n2 lower than the refractive index n1 in the phosphor layer 11 are alternately stacked. The photonic crystal 5 has a first photonic band and a second photonic band. The excitation light has a frequency near the band edge in the second photonic band.

According to the light emitting device 2 described above, in the light emitting element 10 that emits fluorescence, it is possible to reduce light density quenching due to excitation light applied to the light emitting element 10.

(Modification)
The light emitting element 10 according to the first embodiment includes a photonic crystal 5. In the light emitting device according to the present disclosure, a periodic structure like the photonic crystal 5 may be partially provided. This modification will be described with reference to FIG.

FIG. 6 is a view for explaining a light emitting element 10A according to a modification of the first embodiment. The light emitting element 10A according to this modification includes a photonic crystal 5 and a bulk structure 6, as shown in FIG. The bulk structure 6 is made of, for example, the same material as the phosphor layer 11 of the photonic crystal 5 or a material having the same fluorescence characteristics. The photonic crystal 5 is stacked on the −X side (excitation light incident side) of the bulk structure 6.

In the light-emitting device 2, it is considered that light density quenching due to excitation light is significant on the incident side of excitation light in the light-emitting element 10A. Therefore, in the light emitting element 10A according to this modification, the photonic crystal 5 is provided on the incident side of the excitation light, and a bulk phosphor (bulk structure 6) is used for the remaining part.

As an example, in the photonic crystal 5, 200 layers of the phosphor layer 11 and the low refractive index layer 12 are laminated, the thickness TH1 of the phosphor layer 11 per layer is 70 nm, and the phosphor absorptance α is Consider the case of 1000 cm ⁻¹ . In this case, the total thickness of the portions of the phosphor layer 11 in the photonic crystal 5 is 14 μm. In this case, assuming that the light intensity of the excitation light before entering the light emitting element 10A is I0, the light intensity after the excitation light has propagated through the photonic crystal 5 can be calculated as follows.

I0 * exp (−0.0014 * 1000) = 0.247 * I0 (4)
According to the above equation (4), the light intensity after propagating through the photonic crystal 5 is attenuated by about 1/4 times. Therefore, by providing the photonic crystal 5 on the −X side of the bulk structure 6 as described above, when the excitation light enters the bulk structure 6 through the photonic crystal 5, the light intensity of the excitation light is about 1 / 4 times.

In the bulk structure 6, since the light intensity of the excitation light is reduced through the photonic crystal 5, the influence of light density quenching is suppressed. Therefore, the bulk structure 6 can efficiently absorb excitation light and convert it into fluorescence. The thickness of the bulk structure 6 can be set as appropriate in consideration of the light intensity of the excitation light reduced by the photonic crystal 5 to such a degree that the excitation light is assumed to be sufficiently absorbed. (For example, 100 μm to 200 μm).

As described above, the light emitting element 10A according to this modification further includes the bulk structure 6 made of a phosphor that emits fluorescence. The photonic crystal 5 that is a periodic structure is provided closer to the incident side (−X side) of the excitation light than the bulk structure 6. Thereby, light density quenching can be reduced in the photonic crystal 5, and excitation light can be efficiently converted into fluorescence even in the bulk structure 6.

(Other embodiments)
As described above, the first embodiment and the modifications thereof have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, substitutions, additions, omissions, and the like are appropriately performed. Moreover, it is also possible to combine each component demonstrated by each said embodiment into a new embodiment. Accordingly, other embodiments will be exemplified below.

In each of the above embodiments, the light emitting element 10 in the transmissive phosphor wheel 20 has been described. However, the light emitting element according to the present disclosure is not limited to the transmission type, but can be applied to a reflection type phosphor wheel. The reflective light emitting element 10B will be described with reference to FIG.

FIG. 7 is a diagram illustrating the configuration of a light emitting device 10B according to another embodiment. In the light emitting element 10B of this example, the substrate 16 and the dichroic filter 17 provided on the −X side are omitted in the same configuration as that of the first embodiment (see FIG. 2), and instead the metal substrate 15 and the adhesive layer are disposed on the + X side. 14 is provided. The metal substrate 15 is made of, for example, silver, and has a reflective surface 15a that reflects light such as fluorescence on the side opposite to the incident side (−X side) of excitation light (+ X side) in the light emitting element 10B. The adhesive layer 14 is composed of various adhesives, and adheres the photonic crystal 5 and the metal substrate 15.

In the light emitting element 10B of this example, light propagating in the + X direction is reflected by the reflecting surface 15a of the metal substrate 15 and propagates in the -X direction. For this reason, as in the first embodiment, when the excitation light is incident in the + X direction from the −X side, the fluorescence converted from the excitation light is emitted in the −X direction of the light emitting element 10. The reflective surface 15a of the light emitting element 10B may be formed by a metal coating or the like.

As described above, the light emitting element 10B of this example is further provided with the reflecting surface 15a that reflects light on the side opposite to the excitation light incident side (−X side) (+ X side). Thereby, the light emitting element 10B emits the converted fluorescence so as to reflect the incident excitation light.

In each of the above embodiments, the low refractive index layer 12 is used as the object layer in the light emitting elements 10 to 10B. In the light emitting device according to the present disclosure, the object layer is not limited to the low refractive index layer 12 and may be a high refractive index layer having a refractive index higher than that of the phosphor layer 11.

In this case, a photonic crystal having a periodic structure of the phosphor layer 11 and the high refractive index layer is configured so that the vicinity of the PBE on the first photonic band side matches the angular frequency of the excitation light (see FIG. 4). ). Thereby, in the said photonic crystal, when excitation light injects, it can set so that the peak of the intensity distribution of an electric field may be located in a high refractive index layer.

As described above, the refractive index in the object layer may be higher than the refractive index in the phosphor layer 11. In this case, the angular frequency of the photonic band edge in the first photonic band is an angular frequency near the angular frequency of the excitation light. Specifically, the angular frequency of the photonic band edge in the first photonic band is higher than the angular frequency of the excitation light. Thereby, the optical density quenching in the light emitting element 10 can be reduced using a high refractive index layer.

Further, in each of the above embodiments, quantum dots are used as the phosphors in the phosphor layer 11 in the light emitting elements 10 to 10B. In the present disclosure, the phosphor in the phosphor layer or the like is not limited to the quantum dot, and various phosphor materials may be used, for example, YAG.

In each of the above embodiments, the example in which the light emitting device 2 converts the excitation light of blue light into fluorescence and outputs yellow light has been described. The light emitting device according to the present disclosure is not limited to this. For example, the light emitting device may convert part of the excitation light of blue light into yellow light and generate white light by combining the remaining blue light. In this case, a separate blue light source can be omitted in the projector 1.

In the present disclosure, the excitation light is not limited to blue light, and may be light in various wavelength bands. Further, the fluorescence is not limited to yellow light, and may be light in various wavelength bands. As described above, the light emitting device according to the present disclosure may output various types of light based on various types of excitation light.

In each of the above embodiments, the application example in which the light emitting device 2 is applied to the projector 1 has been described. The light-emitting device according to the present disclosure is not limited to the projector 1 and can be applied to various technologies using fluorescence emission based on excitation light.

In each of the above embodiments, the light emitting device 2 includes the light emitting element 10 incorporated in the phosphor wheel 20. The light emitting device according to the present disclosure may include the light emitting element according to the present disclosure without being incorporated in the phosphor wheel. For example, the rotating device 22 may be omitted from the light emitting device 2 when the light emitting element is not particularly required to be cooled or when it can be cooled by another mechanism.

As described above, the embodiments have been described as examples of the technology in the present disclosure. For this purpose, the accompanying drawings and detailed description are provided.

Accordingly, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to illustrate the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

In addition, since the above-described embodiments are for illustrating the technique in the present disclosure, various modifications, substitutions, additions, omissions, and the like can be made within the scope of the claims or an equivalent scope thereof.

The present disclosure can be applied to various technologies using fluorescence emission based on excitation light, for example, a projector.

10, 10A, 10B Light emitting element 11 Phosphor layer 12 Low refractive index layer (object layer)
13 Quantum dot 2 Light emitting device 41 Excitation light source 5 Photonic crystal (periodic structure)

Claims

A light-emitting element that emits fluorescence based on excitation light,
A periodic structure including a plurality of phosphor layers containing a phosphor that emits fluorescence, and a plurality of object layers having a refractive index different from the refractive index of the plurality of phosphor layers;
The plurality of phosphor layers and the plurality of object layers so that the plurality of peaks of the intensity distribution of the electric field of the excitation light are located in the plurality of object layers when the excitation light is incident on the periodic structure. A light emitting device in which are alternately and periodically stacked.
The periodic structure includes a photonic band gap, a first photonic band that defines a dispersion relationship of light having a frequency smaller than a frequency corresponding to the photonic band gap, and a frequency corresponding to the photonic band gap. The light-emitting element according to claim 1, further comprising: a second photonic band that defines a dispersion relationship of light having a larger frequency.
The refractive index in the plurality of object layers is lower than the refractive index in the plurality of phosphor layers,
The light emitting device according to claim 2, wherein an angular frequency of a photonic band edge in the second photonic band is lower than an angular frequency of the excitation light.
The refractive index in the plurality of object layers is higher than the refractive index in the plurality of phosphor layers,
The light emitting device according to claim 2, wherein an angular frequency of a photonic band edge in the first photonic band is higher than an angular frequency of the excitation light.
It further comprises a bulk structure composed of phosphors that emit fluorescence.
The light-emitting element according to any one of claims 1 to 4, wherein the periodic structure is provided closer to the incident side of the excitation light than the bulk structure.
6. The light emitting device according to claim 1, further comprising a reflection surface that reflects light on a side opposite to the incident side of the excitation light.
The plurality of phosphor layers include at least 10 phosphor layers;
The light emitting device according to any one of claims 1 to 6, wherein the plurality of object layers include at least 10 object layers.
A light emitting device according to any one of claims 1 to 7,
A light emitting device comprising: an excitation light source that irradiates the light emitting element with the excitation light.