JP2001297874A - Luminescence device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminescence device being applicable not only for a display object but for optical communications, of which the spectrum width of luminescence wavelength is sharply narrow compared with a conventional organic EL light emission element, the wavelength selection nature excels, and the light emission has directivity. SOLUTION: An end-surface light emitting type luminescence device 1000 has a substrate 10, an anode 12, an organic luminescence layer 16 that can emit light by electroluminescence, and a negative electrode 18. A diffraction grating 14 is arranged between the anode 12 and the luminescence layer 16. The diffraction grating 14 has a 1st medium layer 14a comprising materials constituting the anode 12, and a 2nd medium layer 14b comprising materials constituting the organic luminescence layer 16. The anode 12 has a thickness T defined with a formula of T<=(λ/550)×T0 (nm). Here, λ shows the wavelength of the emitted light, and T0 shows the thickness of the anode in which a combination efficiency of the diffraction grating becomes not less than 10-2 (μm-1) in case the wavelength λis 550 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using EL (electroluminescence).

[0002]

2. Description of the Related Art For example, a semiconductor laser is used as a light source used in an optical communication system. A semiconductor laser is preferable because it has excellent wavelength selectivity and can emit a single-mode light, but requires many times of crystal growth and is not easy to fabricate.
Further, the semiconductor laser has a drawback that the light emitting material is limited and light of various wavelengths cannot be emitted.

Further, the conventional EL light emitting device has a wide spectral width of an emission wavelength and is applied to some uses such as a display body, but is used for an application requiring light with a narrow spectral width such as optical communication. Was unsuitable.

It is an object of the present invention to provide a light emitting device having a spectral width of an emission wavelength which is much narrower than that of a conventional EL light emitting device, and has directivity, which can be applied not only to a display but also to optical communication.
A light emitting device is provided.

[0005]

A light emitting device according to the present invention comprises a substrate, an anode, a light emitting layer capable of emitting light by electroluminescence, a cathode, and a diffraction element disposed between the anode and the light emitting layer. A grid, wherein the anode comprises:
It has a thickness T that satisfies the following equation (1).

T ≦ (λ / 550) × T0 (nm) Equation (1) where λ indicates the wavelength of the emitted light, and T0 indicates that the wavelength λ is 550.
The coupling efficiency of the diffraction grating at 10 nm is 10 ⁻² (μm ⁻¹ ).
Above shows a ^{(10 -2 ~10 0 (μm -1} )) to become a thickness of the anode.

According to this light emitting device, electrons and holes are injected into the light emitting layer from a pair of electrode layers, that is, a cathode and an anode, and the electrons and holes are recombined in the light emitting layer to form molecules. Light is generated when returning from the excited state to the ground state. And the light generated in the light emitting layer is a diffraction grating,
That is, a grating in which two types of medium layers having different refractive indexes are alternately and periodically arranged has wavelength selectivity and directivity.

What is characteristic of the present invention is that the coupling efficiency of the diffraction grating can be increased and the light confinement coefficient of the cathode can be reduced by making the anode have the above-mentioned predetermined thickness. As a result, the light-emitting device of the present invention can efficiently return the light emitted from the light-emitting layer by the diffraction grating, and further, because the light absorption at the cathode is small, the light of the desired wavelength having a small spectral width is obtained. Can be obtained with high efficiency.

Further, by controlling the thickness of the anode, the polarization control between the TE mode and the TM mode can be easily performed, and in particular, a TE wave having a sharp propagation mode can be efficiently obtained. Details of these reasons will be described later.

The diffraction grating is preferably a distributed feedback type or a distributed Bragg reflection type diffraction grating. Thus, by forming a distributed feedback type or a distributed Bragg reflection type diffraction grating, the light obtained in the light emitting layer resonates, and as a result, it has wavelength selectivity, narrow emission spectrum width, and excellent directivity. Light having a property can be obtained.
In these diffraction gratings, the pitch and depth of the diffraction grating are set according to the wavelength of the emitted light.

Further, the diffraction grating of the distributed feedback type has a wavelength of λ /
By using a four-phase shift structure or a gain-coupling type structure, emitted light can be made to have a single mode. Here, λ represents the wavelength of light in the optical waveguide.

In particular, it is a desirable configuration common to the light emitting devices according to the present invention that the diffraction grating is of a distributed feedback type and further has a λ / 4 phase shift structure or a gain coupling type structure.

The light emitting layer preferably contains an organic light emitting material as a light emitting material. By using an organic light emitting material, a wider range of materials can be selected than in the case of using a semiconductor material or an inorganic material, and light of various wavelengths can be emitted.

Such a light emitting device can take the following modes (a) and (b), for example.

(A) The light-emitting device according to the first aspect has a light-emitting device of 450 to 650.
a light emitting device capable of emitting light having a wavelength λ in the range of nm, a substrate, an optically transparent anode, a light emitting layer capable of emitting light by electroluminescence, a cathode, and a light emitting device between the anode and the light emitting layer. And a diffraction grating having a first medium layer made of a material constituting the anode and a second medium layer made of a material constituting the light emitting layer,
When the refractive index n (anode) of the anode and the refractive index n (EL) of the light emitting layer have a relationship of n (anode)> n (EL), the anode has the following formulas (1) and (1). 2) has a thickness T that satisfies 2).

T ≦ (λ / 550) × T 0 (nm) Formula (1) T 0 = 600 Formula (2) (b) The light emitting device of the second embodiment has a light having a wavelength λ in the range of 450 to 650 nm. A substrate, an optically transparent anode, a light emitting layer capable of emitting light by electroluminescence, a cathode, and disposed between the anode and the light emitting layer to form the anode. A diffraction grating having a first medium layer made of a material to be formed and a second medium layer made of a material forming the light emitting layer, wherein the refractive index n (anode) of the anode and the refractive index of the light emitting layer The rate n (EL) is
When n (anode) <n (EL), the anode has a thickness T that satisfies the following equations (1) and (3).

T ≦ (λ / 550) × T 0 (nm) Expression (1) T 0 = 1000 Expression (3) (c) The light emitting device of the third embodiment has a light having a wavelength λ in the range of 450 to 650 nm. A substrate, an optically transparent anode, a light emitting layer capable of emitting light by electroluminescence, a cathode, and disposed between the anode and the light emitting layer to form the anode. A diffraction grating having a first medium layer made of a material to be formed and a second medium layer made of a material constituting the light emitting layer, wherein the anode has a maximum thickness of about 820-1200 nm.

[0018] In the light emitting device according to these aspects, the diffraction grating is disposed between the anode and the light emitting layer. According to the device having this configuration, light generated in the light emitting layer resonates directly with the diffraction grating in a region including the light emitting layer, and as a result, wavelength is selected and emitted with excellent directivity.

When the light emitting layer is an organic light emitting layer using an organic light emitting material, the light emitting layer may further include at least one of a hole transport layer and an electron transport layer. The layer functioning as the cladding layer may be a layer having a lower refractive index than the light propagation layer (core layer), and is not limited to a layer only for confining light, but may also be an electrode layer, a substrate, a hole transport layer, It can also serve as an electron transport layer and the like.

Next, some of the materials that can be used for each part of the light emitting device according to the present invention will be described. These materials are only a part of known materials, and it is a matter of course that materials other than those exemplified can be selected.

(Light Emitting Layer) The material of the light emitting layer is selected from known compounds in order to obtain light having a predetermined wavelength. The material of the light emitting layer may be either an organic compound or an inorganic compound, but is preferably an organic compound from the viewpoint of abundant types and film-forming properties.

Such organic compounds include, for example,
Aromatic diamine derivatives (TPD), oxydiazole derivatives (PBD), oxydiazole dimers (OXD) disclosed in JP-A-10-153967
-8), distilylylene derivative (DSA), beryllium-benzoquinolinol complex (Bebq), triphenylamine derivative (MTDATA), rubrene, quinacridone, triazole derivative, polyphenylene, polyalkylfluorene, polyalkylthiophene, azomethine zinc complex, Porphyrin zinc complex, benzoxazole zinc complex, phenanthroline europium complex and the like can be used.

More specifically, as a material for the organic light emitting layer, JP-A-63-70257 and JP-A-63-1758 can be used.
No. 60, JP-A-2-135361, 2-1.
JP-A-35359, JP-A-3-152184, JP-A-8-248276 and JP-A-10-1539
Known materials such as those described in JP-A-67 can be used. These compounds may be used alone or as a mixture of two or more.

As inorganic compounds, ZnS: Mn (red region), ZnS: TbOF (green region), SrS: C
u, SrS: Ag, SrS: Ce (blue region), and the like.

(Substrate) Known inorganic and organic materials can be used for the substrate or the cladding layer provided if necessary.

Representative inorganic materials include, for example,
As disclosed in JP-A-5-273427, Ti
O_Two, TiO_Two-SiO_TwoMixture, ZnO, Nb_TwoO_Five, S
i_ThreeN _Four, Ta_TwoO_Five, HfO_TwoOr ZrO_TwoFor example
Can be

As typical organic materials, known resins such as various thermoplastic resins, thermosetting resins, and photocurable resins can be used. These resins are appropriately selected in consideration of a method of forming a layer and the like. For example, by using a resin that can be cured by at least one of heat and light, a general-purpose exposure apparatus, a baking furnace, a hot plate, or the like can be used.

As such a substance, for example, there is an ultraviolet curable resin disclosed in Japanese Patent Application No. 10-279439 filed by the present applicant. Acrylic resin is suitable as the UV-curable resin. By using various commercially available resins and photosensitizers, it is possible to obtain an ultraviolet-curable acrylic resin which is excellent in transparency and can be cured by a short-term treatment.

Specific examples of the basic constitution of the ultraviolet-curable acrylic resin include a prepolymer, an oligomer and a monomer.

As the prepolymer or oligomer,
For example, acrylates such as epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, and spiroacetal acrylates; methacrylates such as epoxy methacrylates, urethane methacrylates, polyester methacrylates, and polyether methacrylates; Is available.

As the monomer, for example, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N-vinyl-2-pyrrolidone, carbitol acrylate, tetrahydrofurfuryl acrylate, isovol Monofunctional monomers such as nyl acrylate, dicyclopentenyl acrylate, and 1,3-butanediol acrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol diacrylate,
Bifunctional monomers such as neopentyl glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
Polyfunctional monomers such as pentaerythritol triacrylate and dipentaerythritol hexaacrylate can be used.

(Hole transporting layer) As a material of the hole transporting layer provided as necessary, a material used as a hole injecting material of a known photoconductive material or a hole injecting layer of an organic light emitting device can be used. It can be used by selecting from known ones. The material of the hole transport layer has a function of injecting holes or blocking electrons, and may be an organic substance or an inorganic substance. As a specific example, see, for example,
No. 48276 can be exemplified.

(Electron transporting layer) The material of the electron transporting layer provided as needed may have a function of transmitting electrons injected from the cathode to the organic light emitting layer, and the material may be a known substance. You can choose from. Specific examples thereof include those disclosed in JP-A-8-248276.

(Electrode layer) As the cathode, an electron-injecting metal, an alloy electrically conductive compound having a small work function (for example, 4 eV or less), and a mixture thereof can be used.
Examples of such an electrode material include, for example, JP-A-8-248.
No. 276 can be used.

As the anode, a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function (for example, 4 eV or more) can be used. When an optically transparent material is used for the anode, CuI, ITO, SnO
₂ , conductive transparent materials such as ZnO can be used,
When transparency is not required, a metal such as gold can be used.

In the present invention, the method of forming the diffraction grating is not particularly limited, and a known method can be used. Representative examples are shown below.

Lithography Method A positive or negative resist is exposed and developed with ultraviolet rays or X-rays to pattern the resist layer.
Create a diffraction grating. As a patterning technique using a resist such as polymethyl methacrylate or a novolak resin, there are, for example, JP-A-6-224115 and JP-A-7-20637.

A technique for patterning polyimide by photolithography is disclosed in, for example,
181689 and 1-222141. Furthermore, as a technique for forming a diffraction grating of polymethyl methacrylate or titanium oxide on a glass substrate by using laser ablation, there is, for example, Japanese Patent Application Laid-Open No. 10-59743.

Method of Forming Refractive Index Distribution by Light Irradiation A light having a wavelength that causes a change in the refractive index is radiated to a light propagating portion, and a portion having a different refractive index is periodically formed in the light propagating portion. To form As such a method, it is particularly preferable to form a layer of a polymer or a polymer precursor, partially polymerize the layer by light irradiation or the like, and periodically form regions having different refractive indexes to form a diffraction grating. . As this kind of technology, for example, Japanese Patent Laid-Open No. 9-31
1238, 9-178901, 8-1
Nos. 5506, 5-297202, 5-3
No. 2523, No. 5-39480, No. 9-21
Nos. 1728, 10-26702, 10-
Nos. 8300 and 2-51101.

Hot stamping method using a thermoplastic resin
No. 201907), stamping using an ultraviolet curable resin (Japanese Patent Application No. 10-279439), stamping using an electron beam curable resin (Japanese Unexamined Patent Publication No. 7-235075).
A diffraction grating is formed by stamping as described in Japanese Unexamined Patent Publication (Kokai) No. H11-209686.

Etching Method A thin film is selectively removed and patterned by using lithography and etching techniques to form a diffraction grating.

The method of forming the diffraction grating has been described above. In short, the diffraction grating only needs to be composed of two regions having different refractive indices, and the two regions are formed by two kinds of materials having different refractive indices. It can be formed by a method, a method of forming two regions having different refractive indexes by partially modifying a kind of material, or the like.

Each layer of the light emitting device can be formed by a known method. For example, a suitable film forming method is selected for the light emitting layer depending on its material, and specific examples include a vapor deposition method, a spin coating method, an LB method, and an ink jet method.

[0044]

FIG. 1 shows an edge-emitting type light emitting device (hereinafter referred to as "organic light emitting device") 10 according to the present embodiment.
FIG. 2 is a perspective view schematically showing 00, and FIG.
It is sectional drawing of the principal part along the A line.

(Structure) The organic light emitting device 1000 comprises a substrate 1
0, the anode 12, the organic light emitting layer 16 and the cathode 18
The layers are stacked in this order. This organic light emitting device 1
000, the refractive index of the substrate 10 is set smaller than the refractive index of the anode 12.

The diffraction grating 14 is provided between the anode 12 and the organic light emitting layer 16. The diffraction grating 14 has a first medium layer 14 a and a second medium layer 14 having different refractive indexes.
b. The first medium layer 14a is made of a material constituting the anode 12, and the second medium layer 14b is made of the organic light emitting layer 1
6 is composed of the substance.

Since the anode 12 constitutes the first medium layer 14a of the diffraction grating 14, it is made of a conductive material transparent to emitted light. As the material of such a transparent electrode, the above-mentioned materials can be used. Also, the anode 12
It is desirable to have a thickness in a predetermined range from the viewpoint of the propagation mode. The propagation mode and the thickness of the anode 12 will be described later.

The diffraction grating 14 is preferably a distributed feedback type diffraction grating. By forming a distributed feedback type diffraction grating in this manner, light can resonate in the optical waveguide, and light with excellent wavelength selectivity and directivity and a narrow emission spectrum width can be obtained. Further, although not shown, the diffraction grating 14 preferably has a λ / 4 phase shift structure or a gain coupling type structure. By having the λ / 4 phase shift structure or the gain-coupling type structure as described above, the emitted light can be made into a single mode.

The organic light emitting layer 16 and the cathode 18 are made of the above-mentioned materials. Further, the thicknesses of the organic light emitting layer 16 and the cathode 18 are not particularly limited. The organic light emitting layer 16
For example, considering light emission function, conductivity, etc., 100 to 1
It can have a thickness of 000 nm. In addition, cathode 1
8 is 50 to 1000 in consideration of, for example, conductivity.
nm.

In the organic light emitting device 1000, the core layer 100 is mainly constituted by the anode 12, the diffraction grating 14 and the organic light emitting layer 16, and the cladding layer is constituted by the substrate 10 and the cathode 18.

Another structure: In the organic light emitting device 1000, as shown in FIG.
Is formed, and a second coating layer 20b having high reflectivity is formed on the other end face. For these coating layers, for example, a dielectric multilayer mirror generally used in a semiconductor DFB laser can be used.

For the method of manufacturing the organic light emitting device 1000 such as the diffraction grating and the organic light emitting layer, and the materials constituting each layer, the above-described methods and materials can be appropriately used. For example, in forming the diffraction grating 14, a method using stamping, which has a relatively simple process, can be preferably used.

(Analysis of Propagation Mode) Next, the propagation mode of the light emitting device having the basic configuration of the organic light emitting device 1000 of the present embodiment will be described with reference to FIG. FIG.
3 shows a basic configuration of the light emitting device and propagation modes corresponding to each component thereof. The configuration of the light emitting device is
1 and 2 are denoted by the same reference numerals. In FIG. 3, a region indicated by reference numeral “a” corresponds to the diffraction grating 14, and a region indicated by reference numeral “b” corresponds to the cathode 18.
It corresponds to.

From the propagation mode, the coupling efficiency at the diffraction grating 14, the light confinement coefficient at the cathode 18, and the like can be analyzed. The propagation mode is, for example, the document "Internatio
nalJournal of Optoelectronics, 1995, vo
l. 10, No. 5, pages 331-335 ". Hereinafter, the coupling efficiency and the confinement coefficient will be described in detail.

Coupling efficiency of diffraction grating: As in the light emitting device of the present invention, periodic unevenness (corresponding to the diffraction grating 14 in this embodiment) is provided in a part of the multilayer structure to reduce the wavelength dispersion of light. When controlling, it is important that the propagation mode is efficiently coupled to the diffraction grating 14. Coupling efficiency (Coup) is usually used as an index indicating the degree of coupling between the propagation mode and the diffraction grating.
ling Coefficient) is used. The coupling efficiency is represented by, for example, equations (14) and (15) described in the above-mentioned literature. The coupling efficiency of the diffraction grating reflects the size of the area S100 of the region indicated by the symbol “a” in FIG. In other words, when the conditions for the two medium layers constituting the diffraction grating and the factors relating to the shape of the diffraction grating are fixed, the coupling efficiency of the diffraction grating increases as the area S100 increases. The contribution of the diffraction grating 14 to the propagation mode increases as the coupling efficiency increases.

The propagation mode changes depending on the number of layers constituting the light emitting device, the material and thickness of the layers, and the coupling efficiency also changes accordingly. In the light emitting device, it is important to increase the coupling efficiency in the diffraction grating 14 in order to efficiently return emitted light in the diffraction grating and efficiently obtain light of a predetermined wavelength. To that end, the coupling efficiency is preferably 10 ^-2 (μm ^-1) or more (10 ^-2 ~10 ⁰ (μ
is ^{1 (μm -1)} or more ^- m ^-1)), more preferably 10.

Confinement Coefficient at Cathode: In the light emitting device 1000, the cathode 18 is usually made of metal, so that light absorption becomes very large. When light emission is observed from the anode side as in a display, light absorption at the cathode 18 is not so problematic. However, in the light emitting device of the edge emission type as in the present invention, it is presumed that the absorption of light at the cathode 18 becomes a serious problem in terms of luminous efficiency. Therefore, in order to increase the luminous efficiency of the light emitting device, it is necessary that the propagation mode does not overlap with the cathode 18 as much as possible.

As an index indicating the overlap between the cathode and the propagation mode, the confinement coefficient at the cathode is usually used. Here, the confinement coefficient is an integral value of the propagation mode of the region indicated by the symbol “b” in FIG. 3 and reflects the area S200 of this region. That is, the confinement coefficient is determined by the area S
It increases in proportion to 200. Then, in order to reduce light absorption at the cathode, it is necessary to make the confinement coefficient at the cathode as close to zero as possible.

The propagation mode changes depending on the number of layers constituting the light emitting device, the material and thickness of the layers, and the confinement coefficient changes accordingly. In the light emitting device, in order to achieve higher luminous efficiency, it is important to reduce the light confinement coefficient at the cathode 16. For that purpose, the confinement coefficient is preferably 0.1 or less, more preferably 0.
05 or less.

The thickness of the anode 12; the thickness of the anode 12 affects the coupling efficiency of the diffraction grating and the confinement coefficient at the cathode, and has a certain correlation. Further, their coupling efficiency and confinement coefficient depend on the magnitude relationship between the refractive index of the anode 12 and the refractive index of the organic light emitting layer 16. Specifically, the relationship between the thickness of the anode 12 and the coupling efficiency and confinement coefficient is as follows. The result of the simulation, which is the main basis for the thickness of the anode 12, will be described later.

(A) In a light emitting device capable of emitting light having a wavelength λ in the range of 450 to 650 nm, it is desirable that the following relationship be satisfied in consideration of the coupling efficiency at the diffraction grating.

The refractive index n (anode) of the anode 12 and the refractive index n (EL) of the organic light emitting layer 16 are such that n (anode)> n (E
In the relationship of L), the anode 12 preferably has a thickness T that satisfies the following equations (1) and (2).

T ≦ (λ / 550) × T0 (nm) Formula (1) T0 = 600 Formula (2) Here, T0 has a coupling efficiency of 10 ⁻² (μm ⁻¹ ) or more (1
0 ^-2 10 ⁰ preferable numerical order is (μm ^-1)). Further, in order for the coupling efficiency to be 10 ⁻¹ (μm ⁻¹ ) or more, it is preferable that T0 = 150 nm.

(B) In a light emitting device capable of emitting light having a wavelength λ in the range of 450 to 650 nm, the refractive index n (an
ode) and the refractive index n (EL) of the organic light emitting layer 16 is n (a
node) <n (EL), the anode 12 preferably has a thickness T that satisfies the following equations (1) and (3).

T ≦ (λ / 550) × T0 (nm) Formula (1) T0 = 1000 Formula (3) Here, T0 has a coupling efficiency of 10 ⁻² (μm ⁻¹ ) or more (1)
0 ^-2 10 ⁰ preferable numerical order is (μm ^-1)). Further, it is preferable that T0 = 250 nm so that the coupling efficiency is 10 ^-1 (μm ^-1 ) or more.

(C) In a light emitting device capable of emitting light having a wavelength λ in the range of 450 to 650 nm, considering the relationship between the TE mode and the TM mode, that is, the difference in the confinement coefficient between the TE mode and the TM mode, It is desirable that the following relationship be established. FIG. 1 shows the electric field, the magnetic field, and the direction of light propagation in the TE mode and the TM mode.

The refractive index n (anode) of the anode 12 and the refractive index n (EL) of the organic light emitting layer 16 are such that n (anode)> n (E
In the relationship of L), the anode 12 preferably has a thickness T that satisfies the following equations (1) and (2).

T ≦ (λ / 550) × T0 (nm) Expression (1) T0 = 350 Expression (2) Here, T0 is a difference between the TE mode and the TM mode.
This is a preferable value because it is 1 or more. Furthermore, TE
In order for the difference between the mode and the TM mode to be 0.3 or more, it is preferable that T0 = 200 nm.

(D) In a light emitting device capable of emitting light with a wavelength λ in the range of 450 to 650 nm, considering the relationship between the TE mode and the TM mode, that is, the difference in the confinement coefficient between the TE mode and the TM mode, It is desirable that the following relationship be established.

The refractive index n (anode) of the anode 12 and the refractive index n (EL) of the organic light emitting layer 16 are such that n (anode) <n (E
In the relationship of L), the anode 12 preferably has a thickness T that satisfies the following equations (1) and (3).

T ≦ (λ / 550) × T0 (nm) Expression (1) T0 = 700 Expression (3) Here, T0 is 0.
This is a preferable value because it is 1 or more. Furthermore, TE
In order for the difference between the mode and the TM mode to be 0.3 or more, it is preferable that T0 = 250 nm.

Considering the above comprehensively, 450 to 6
In a light emitting device that can emit light with a wavelength λ in the range of 50 nm, the anode 12 has a maximum thickness of about
Desirably, it is 820 to 1200 nm.

(Operation and Function) Next, the operation and function of the organic light emitting device 1000 will be described.

When a predetermined voltage is applied to the anode 12 and the cathode 18, electrons are injected from the cathode 18 and holes are injected from the anode 12 into the organic light emitting layer 16. In the organic light emitting layer 16, the electrons and holes are recombined to generate excitons, and when the excitons are deactivated, light such as fluorescence or phosphorescence is generated. The wavelength λ of light is desirably in the range of the wavelength of visible light (450 to 650 nm).

Light generated in the organic light emitting layer 16 is partially reflected by the substrate 10 and the cathode 18, and partially propagates as it is in the anode 12 and the organic light emitting layer 16. In the core layer 100, light is distributed-propagation-type propagated by the diffraction grating 14, propagates in the core layer 100 toward the end face, and forms the first coating layer 10 having a low reflectance.
0a. Since the emitted light is distributed and fed back by the core layer 100 by the diffraction grating 14, the emitted light has wavelength selectivity, a narrow emission spectrum width, and excellent directivity. Furthermore, by making the diffraction grating 14 a λ / 4 phase shift structure or a gain-coupling structure, the outgoing light can be made into a single mode. Where λ
Represents the wavelength of light in the optical waveguide.

The characteristic features of this embodiment are as follows.
When the anode 12 has a thickness in the above-described predetermined range, the coupling efficiency of the diffraction grating 14 can be increased,
The confinement coefficient at the cathode can be reduced. As a result, the light emitting device 1000 can efficiently return the light emitted from the organic light emitting layer 16 by the diffraction grating 14, and furthermore, the cathode 1
8 also absorbs less light. Therefore, the light emitting device 100
According to 0, light of a desired wavelength having a small spectral width can be obtained with high efficiency.

Further, when the anode 12 has the thickness in the above-described range, the polarization control between the TE mode and the TM mode can be easily performed, and in particular, a TE wave having a sharp propagation mode can be efficiently obtained.

(Simulation Example) With respect to the light emitting device of the present invention, the relationship between the light confinement coefficient at the cathode, the coupling efficiency of the diffraction grating, and the thickness of the anode was examined by simulation. The light-emitting device used for the simulation is the basic structure of the light-emitting device 1000 shown in FIGS. 1 and 2, that is, a substrate 10, an anode 12, a diffraction grating (consisting of an anode and an organic light-emitting layer) 14, an organic light-emitting layer. 16 and a cathode 18.

(1) Sample of Light Emitting Device ITO was used as the anode, and its thickness T1 was 150 nm.
(Including the portion of the diffraction grating), and the thickness T2 of the diffraction grating is 50 n
m, the thickness T3 of the organic light emitting layer was set to 100 nm (including the portion of the diffraction grating), and the thickness T4 of the cathode was set to 5000 nm. The substrate was sufficiently thicker than other layers, for example, set to 5000 nm.

As a sample, (A) a sample in which the refractive index n (anode) of the anode (hereinafter referred to as the refractive index n (ITO)) is larger than the refractive index n (EL) of the organic light emitting layer, ie, n
(ITO)> n (EL) sample (hereinafter referred to as “sample A”), and (B) anode refractive index n (ITO)
Is smaller than the refractive index n (EL) of the organic light emitting layer, that is, a sample of n (ITO) <n (EL) (hereinafter, this is referred to as “sample B”).

(2) Method of Simulation For each of the characteristics described below, only the 0th-order propagation mode was evaluated, and both the TE wave and the TM wave were obtained. The propagation mode is described in the document "InternationalJournal
of Optoelectronics, 1995, vol. 10, N
o. 5, pages 331-335 ".

(3) Results of Simulation Light Confinement Coefficient at Cathode FIG. 4 shows the relationship between the confinement coefficient and the thickness of the anode (ITO layer) in the TE mode obtained for samples A and B, respectively. Show. In FIG. 4, the horizontal axis represents the thickness of the anode, and the vertical axis represents the confinement coefficient of the cathode.

The confinement coefficient of the cathode in the light emitting device is preferably 0.1 or less for the above-mentioned reason. Considering this, the thickness of the anode is not so limited from the viewpoint of the confinement coefficient of the cathode.

FIG. 5 shows the relationship between the coupling efficiency of the diffraction grating and the thickness of the anode (ITO layer) obtained for Samples A and B, respectively. In FIG. 5, the horizontal axis represents the thickness of the anode, and the vertical axis represents the coupling efficiency of the diffraction grating.

The coupling efficiency (logarithmic representation) of the diffraction grating in the light emitting device is preferably 10
^-2 (μm ^-1 ) or more, more preferably 10 ^-1 (μm ^-1 ) or more. Considering this, from the viewpoint of the coupling efficiency of the diffraction grating, the thickness of the anode in the case of the sample A is preferably 600 nm or less, more preferably 150 nm or less. Similarly, the thickness of the anode is, in the case of sample B,
Preferably it is 1000 nm or less, more preferably 250 nm or less.

Consideration from Comparison of TE Wave and TM Wave -1; Coupling Efficiency of Diffraction Grating FIG. 6 shows the difference between the coupling efficiency in the TM mode and the TE mode (the value of the TE wave) obtained for samples A and B. −TM wave value: Δc.c.) is plotted against the thickness of the anode. As the difference Δc.c. in the coupling efficiency is larger, the polarization control is performed more efficiently, and only a TE wave having a sharp propagation mode can be efficiently extracted.

As shown in FIG. 6, the sample B has a difference Δ 、 in the coupling efficiency.
It can be seen that cc is large and that the TE wave can be selectively extracted.

FIG. 7 shows the difference between the confinement coefficient in the TM mode and the TE mode obtained for samples A and B (TM wave value−TE
Wave value: Δc.f.) is plotted against anode thickness.

The larger the difference Δc.f. in the confinement coefficient, the more
Polarization control is performed efficiently and the propagation mode is sharp T
Only the E wave can be efficiently extracted.

For the reason described above, the difference Δc.f.
Is preferably 0.1 or more, more preferably 0.3 or more. Taking this into account, the thickness of the anode is the same as that of sample A
Is preferably 350 nm or less, more preferably 200 n
m or less. Similarly, the thickness of the anode for sample B is preferably 700 nm or less, more preferably 350 nm or less.

Also, from FIG. 7, when the thickness of the anode is 200 nm or less, the sample A (n (ITO)> n (EL))
It is understood that when the thickness of the anode is larger than 200 nm, sample A (n (ITO)> n (EL)) is preferable.

In the above-described embodiment, the case where the organic light emitting layer is used as the light emitting layer has been described, but a light emitting layer made of an inorganic material may be used instead of the organic light emitting layer.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an organic light emitting device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a main part of the organic light emitting device shown in FIG. 1 along line AA.

FIG. 3 is a diagram showing a propagation mode of the light emitting device according to the present invention.

FIG. 4 is a diagram showing the relationship between the thickness of the anode and the light confinement coefficient at the cathode obtained for the light emitting device according to the present invention.

FIG. 5 is a diagram showing the relationship between the thickness of the anode and the coupling efficiency of the diffraction grating, obtained for the light emitting device according to the present invention.

FIG. 6 is a graph showing the relationship between the thickness of the anode and the difference between the coupling efficiency in the TE mode and the coupling efficiency in the TM mode, obtained for the light emitting device according to the present invention.

FIG. 7 is a diagram showing the relationship between the thickness of the anode and the difference between the confinement coefficient in the TE mode and the difference in the confinement coefficient in the TM mode obtained for the light emitting device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 12 Anode 14 Diffraction grating 14a, 14b Medium layer 16 Organic light emitting layer 18 Cathode 100 Core layer

Claims (20)

[Claims] 1. A substrate, an anode, a light-emitting layer capable of emitting light by electroluminescence, a cathode, a diffraction grating disposed between the anode and the light-emitting layer,
The light emitting device, wherein the anode has a thickness T that satisfies the following equation (1). T ≦ (λ / 550) × T0 (nm) Formula (1) Here, λ indicates the wavelength of the emitted light, and T0 indicates that the wavelength λ is 550.
The coupling efficiency of the diffraction grating at 10 nm is 10 ⁻² (μm ⁻¹ ).
The following shows the thickness of the anode. 2. The light emitting device according to claim 1, wherein the wavelength λ is in a range of 450 to 650 nm. 3. The first diffraction grating according to claim 1, wherein the diffraction grating is made of a material constituting the anode.
And a second medium layer made of a material constituting the light emitting layer. 4. The relation according to claim 1, wherein a refractive index n (anode) of the anode and a refractive index n (EL) of the light emitting layer are such that n (anode)> n (EL). , T0 = 600n
m, a light emitting device. 5. The light emitting device according to claim 4, wherein T0 = 500 nm. 6. The light emitting device according to claim 4, wherein T0 = 150 nm. 7. The relation according to claim 1, wherein a refractive index n (anode) of the anode and a refractive index n (EL) of the light emitting layer are n (anode) <n (EL). , T0 = 1000n
m, a light emitting device. 8. The light emitting device according to claim 7, wherein T0 = 250 nm. 9. A light emitting device capable of emitting light having a wavelength λ in the range of 450 to 650 nm, comprising: a substrate; an optically transparent anode; a light emitting layer capable of emitting light by electroluminescence; a cathode; And a diffraction grating having a first medium layer made of a material forming the anode and a second medium layer made of a material forming the light emitting layer, disposed between the light emitting layer and the light emitting layer, When the refractive index n (anode) of the anode and the refractive index n (EL) of the light emitting layer are in a relationship of n (anode)> n (EL), the anode has the following formulas (1) and (2). Thickness T that satisfies
A light emitting device comprising: T ≦ (λ / 550) × T0 (nm) Formula (1) T0 = 600 Formula (2) 10. The light emitting device according to claim 9, wherein T0 = 500 nm. 11. The light emitting device according to claim 9, wherein T0 = 150 nm. 12. A light emitting device capable of emitting light having a wavelength λ in the range of 450 to 650 nm, comprising: a substrate; an optically transparent anode; a light emitting layer capable of emitting light by electroluminescence; a cathode; And a diffraction grating having a first medium layer made of a material forming the anode and a second medium layer made of a material forming the light emitting layer, disposed between the light emitting layer and the light emitting layer, When the refractive index n (anode) of the anode and the refractive index n (EL) of the light-emitting layer satisfy a relationship of n (anode) <n (EL), the anode has the following formulas (1) and (3). Thickness T that satisfies
A light emitting device comprising: T ≦ (λ / 550) × T0 (nm) Expression (1) T0 = 1000 Expression (3) 13. The light emitting device according to claim 12, wherein T0 = 250 nm. 14. A light emitting device capable of emitting light having a wavelength λ in the range of 450 to 650 nm, comprising: a substrate; an optically transparent anode; a light emitting layer capable of emitting light by electroluminescence; a cathode; And a diffraction grating having a first medium layer made of a material forming the anode and a second medium layer made of a material forming the light emitting layer, disposed between the light emitting layer and the light emitting layer, The anode has a maximum thickness of about 820-120, depending on the wavelength λ.
A light emitting device that is 0 nm. 15. The light emitting device according to claim 1, wherein the thickness of the light emitting layer is 100 to 1000 nm. 16. The light emitting device according to claim 1, wherein the diffraction grating is a distributed feedback diffraction grating. 17. The light emitting device according to claim 16, wherein the diffraction grating has a λ / 4 phase shift structure. 18. The light emitting device according to claim 16, wherein the diffraction grating has a gain coupling type structure. 19. The light emitting device according to claim 1, wherein the diffraction grating is a distributed Bragg reflection type diffraction grating. 20. The light emitting device according to claim 1, wherein the light emitting layer contains an organic light emitting material as a light emitting material.