JP2016004721A - Light emission element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emission element that can achieve light of high intensity.SOLUTION: A light emission element 1 has a light emitter 3 for emitting excitation light, a color converter 7 which is provided at the light emission side of the light emitter 3, contains fluorescence material for generating fluorescent light upon irradiation of the excitation light and emits fluorescent light from the fluorescence material to convert the color of light emitted from the light emitter, and a dielectric layer 6 which is provided between the light emitter 3 and the color converter 7 and comprises a dielectric medium 9 containing plural metal nano particles 6 which develops a surface plasmon phenomenon. The average distance from a surface of the color converter 7 which is contact in the dielectric layer 6 till the metal nano particles 5 existing in the dielectric layer 6 is not more than the average diameter of the metal nano particles 5.

Description

  The present invention relates to a light emitting element.

  As one of light-emitting elements used for display devices and the like, an organic electroluminescence element is conventionally known. Hereinafter, electroluminescence is abbreviated as “EL”. As a method for making an organic EL element a multicolor light emitting element, the following Patent Document 1 includes an organic EL material part and a fluorescent material part, and a part of blue light emitted from the organic EL material part is emitted from the fluorescent material part. Discloses an “organic EL element” that realizes multicolor emission by converting into green light or red light.

  In this type of organic EL element, as a means for improving the light emission efficiency and obtaining high intensity light, the following Patent Document 2 resonates a light having a specific wavelength by multiple reflection between a pair of reflective layers, An “organic EL display” having a microresonator structure that enhances strength is disclosed. Patent Document 3 below includes a light emitting layer that emits blue light, a red color conversion layer, a green color conversion layer, and a blue transmission layer, and exhibits a surface plasmon phenomenon in the color conversion layer and the transmission layer. An “organic EL element” containing metal nanoparticles to be disclosed is disclosed. According to Patent Document 3, there is an effect that fluorescence conversion is enhanced by including metal nanoparticles in the color conversion layer and the transmission layer.

Japanese Patent Laid-Open No. 3-152897 JP 2009-205928 A International Publication No. 11/104936

  However, in the organic EL display described in Patent Document 2, it is difficult to accurately adjust the optical distance between a pair of reflective layers for each color. If the optical distance deviates from the optimum value, high intensity light cannot be obtained. Moreover, in the organic EL element described in Patent Document 3, when the emission wavelength of the fluorescent molecule is matched with the resonance wavelength of the metal nanoparticle, the emission from the fluorescent molecule is reabsorbed by the metal nanoparticle. For this reason, it is difficult to greatly increase the luminance.

  One embodiment of the present invention has been made to solve the above-described problems, and an object thereof is to provide a light-emitting element capable of obtaining light with high intensity.

  In order to achieve the above object, a light-emitting element according to one embodiment of the present invention includes a light-emitting portion that emits excitation light and a fluorescence that is provided on the light-emitting side of the light-emitting portion and generates fluorescence when irradiated with the excitation light. A color conversion unit that converts the color of light from the light-emitting unit when the phosphor emits fluorescence, and is provided between the light-emitting unit and the color conversion unit to express a surface plasmon phenomenon A dielectric layer made of a dielectric medium containing a plurality of metal nanoparticles, and from the surface of the color conversion portion in contact with the dielectric layer to the metal nanoparticles present in the dielectric layer The average distance is not more than the average diameter of the metal nanoparticles.

  In the light-emitting element according to one aspect of the present invention, the light emitted from the light-emitting portion may be blue light.

  In the light emitting device according to one aspect of the present invention, the color conversion unit includes a phosphor layer that emits color light other than blue light as the fluorescence, and a light transmission layer that transmits blue light emitted from the light emitting unit. In the color conversion part, the metal nanoparticles are contained in the dielectric layer corresponding to the formation region of the phosphor layer, and the metal nanoparticle is contained in the dielectric layer corresponding to the formation region of the light transmission layer. The structure which does not contain particle | grains may be sufficient.

  In the light emitting device according to one aspect of the present invention, the dielectric medium may have a relative dielectric constant of 1.71 or more and 4.58 or less.

  In the light emitting device according to one aspect of the present invention, the metal nanoparticles have a rod-like shape, and are oriented so that the major axis direction of the metal nanoparticles is substantially directed to the thickness direction of the dielectric layer. May be.

  In the light emitting device of one aspect of the present invention, a color filter may be provided on the light emission side of the color conversion unit.

  In the light emitting device of one embodiment of the present invention, a plurality of metal nanoparticles that express a surface plasmon phenomenon may be contained in the color conversion part.

  In the light emitting device of one embodiment of the present invention, the periphery of the metal nanoparticles may be coated with a dielectric containing phosphor molecules.

  According to one embodiment of the present invention, it is possible to provide a light emitting element capable of obtaining high intensity light.

It is sectional drawing which shows the light emitting element of 1st Embodiment. (A) The figure which shows a mode that an enhancement electric field is formed in the silver nanoparticle vicinity, (B) The graph which shows the wavelength dependence of the electric field enhancement intensity in the silver nanoparticle vicinity when the relative dielectric constant of the surrounding medium changes, (C) is a graph showing the wavelength dependence of the electric field enhancement intensity in the vicinity of silver nanoparticles when the relative permittivity of the surrounding medium is 2.56 in order to enhance blue excitation light. (A) The figure which shows the model for calculating energy transfer efficiency, (B) The graph which shows the wavelength dependence of the normalized electric field strength and molar absorption coefficient in the silver nanoparticle vicinity. (A) The figure which shows the distance of a silver nanoparticle and a fluorescent molecule, (B) The graph which shows the relationship between the distance between silver nanoparticle-fluorescent molecule, and energy transfer efficiency, (C) Shows the wavelength dependence of fluorescence intensity. Graph. (A) A graph showing the relationship between the distance between silver nanoparticles and fluorescent molecules and the energy transfer efficiency, (B) a graph showing the wavelength dependence of the normalized electric field strength and molar extinction coefficient in the vicinity of the silver nanoparticles. . (A) The figure which shows the effect | action of the conventional light emitting element, (B) The figure which shows the effect | action of the light emitting element of this embodiment, (C) The relationship between the fluorescence intensity and the light absorption rate of a silver nanoparticle containing dielectric material layer is shown. Graph. It is a figure used for description of 2nd Embodiment, and is a graph which shows the wavelength dependence of the enhancement of an electric field strength when changing the dielectric constant of a dielectric material medium. It is a figure which shows the effect | action and effect of the light emitting element of 2nd Embodiment, (A) The graph which shows the relationship between the increase in fluorescence and the relative dielectric constant of a dielectric medium, (B) The increase in fluorescence intensity and silver nanoparticle It is a graph which shows the relationship with the light absorption rate of a containing dielectric material layer. It is sectional drawing which shows the light emitting element of 3rd Embodiment. It is a figure which shows a mode that an enhancement electric field is formed in the silver nanorod vicinity. (A) The graph which shows the wavelength dependence of the enhancement of the electric field strength in the silver nanorod vicinity, (B) The graph which shows the relationship between the enhancement of a fluorescence intensity and the light absorption rate of a silver nanoparticle containing dielectric material layer. It is sectional drawing which shows the light emitting element of 4th Embodiment. (A) The figure which shows the spectrum of the light emitted from the organic electroluminescent light emission part, (B) The figure which shows the spectrum of the light emitted from the blue pixel area | region. It is sectional drawing which shows the light emitting element of 5th Embodiment. It is a figure which shows a mode that an enhancement electric field is formed in the silver nanoparticle vicinity. (A) Sectional drawing which shows the color conversion layer of the light emitting element of 5th Embodiment, (B) Sectional drawing which shows the color conversion layer of the light emitting element of 6th Embodiment.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view showing the light emitting device of the first embodiment.
In the following drawings, in order to make each component easy to see, the scale of the size may be varied depending on the component.

  As shown in FIG. 1, the light emitting device 1 of the present embodiment includes a first substrate 2, a light emitting unit 3, a second substrate 4, a dielectric layer 6 including a plurality of metal nanoparticles 5, and a phosphor. A color conversion unit 7 including the third substrate 8; On the first surface 2a of the first substrate 2, the light emitting unit 3 and the second substrate 4 are stacked in this order from the first substrate 2 side. On the second surface 2b of the first substrate 2, the dielectric layer 6, the color conversion unit 7, and the third substrate 8 are laminated in this order from the first substrate 2 side. The light emitting unit 3 is composed of an organic EL element formed on the first substrate 2. The dielectric layer 6 and the color conversion unit 7 are formed on the second surface 2 b of the first substrate 2.

  The light emitting unit 3 emits excitation light for exciting the phosphor of the color conversion unit 7. The color conversion unit 7 is provided on the light emission side (upper layer side in FIG. 1) of the light emitting unit 3. The color conversion unit 7 includes a phosphor that generates fluorescence when irradiated with excitation light. In the color conversion unit 7, the phosphor absorbs excitation light and emits fluorescence having a color different from that of the excitation light. Thereby, the color of the excitation light emitted from the light emitting unit 3 is converted. The dielectric layer 6 is provided between the light emitting unit 3 and the color conversion unit 7. The dielectric layer 6 is composed of a dielectric medium 9 containing a plurality of metal nanoparticles 5 that express a surface plasmon phenomenon.

As the first substrate 2, for example, an inorganic material substrate made of glass, quartz, etc., a plastic substrate containing polyethylene terephthalate, polycarbazole, polyimide, etc., an insulating substrate such as a ceramic substrate containing alumina, etc., or aluminum (Al) A metal substrate containing iron (Fe) or the like, or a substrate coated with an insulator containing silicon oxide (SiO ₂ ) or an organic insulating material on the substrate, or a metal substrate containing Al or the like is anodized on the surface. And a substrate subjected to insulation treatment by the above method. However, the substrates that can be used in this embodiment are not limited to these substrates. For example, when the material of the substrate is glass, deformation is not caused even by a high-temperature process and moisture is not transmitted, which is preferable in that deterioration of the organic EL element can be suppressed. The second substrate 4 can be the same substrate as the first substrate 2.

  Although not shown in FIG. 1, a TFT circuit is provided on the surface of the second substrate 4 on the side facing the first substrate 2. The TFT circuit functions as a switching element and a driving element of the light emitting unit 3. As a specific configuration of the TFT circuit, a known TFT circuit can be used.

  The light emitting unit 3 includes a cathode 11, an anode 12, and an organic light emitting layer 13 sandwiched between the cathode 11 and the anode 12. The organic light emitting layer 13 has a configuration in which, for example, an electron injection layer 14, an electron transport layer 15, a hole prevention layer 16, a light emitter layer 17, a hole transport layer 18, and a hole injection layer 19 are laminated in this order from the cathode 11 side. Have The light emitter layer 17 emits blue light.

The organic light emitting layer 13 is not limited to the configuration of the present embodiment, and may have a single layer structure of the light emitter layer 17 or a multilayer structure including the light emitter layer 17, the hole transport layer 18, the electron transport layer 15, and the like. . For example, although the following nine types of structures are mentioned, this invention is not limited by these.
(1) Light emitter layer
(2) Light emitter layer / hole transport layer (3) Electron transport layer / light emitter layer (4) Electron transport layer / light emitter layer / hole transport layer (5) Electron transport layer / light emitter layer / hole transport Layer / hole injection layer (6) electron injection layer / electron transport layer / light emitter layer / hole transport layer / hole injection layer (7) electron transport layer / hole prevention layer / light emitter layer / hole transport layer / Hole injection layer (8) electron injection layer / electron transport layer / hole prevention layer / light emitter layer / hole transport layer / hole injection layer (9) electron injection layer / electron transport layer / hole prevention layer / Light emitter layer / electron prevention layer / hole transport layer / hole injection layer Here, light emitter layer, hole injection layer, hole transport layer, hole prevention layer, electron prevention layer, electron transport layer and electron injection layer Each of these layers may have a single layer structure or a multilayer structure.

  The light emitting unit 3 may have a structure that exhibits a microcavity effect. As a structure that exhibits the microcavity effect, for example, it is desirable to set the thickness of the organic light emitting layer 13 so as to match the wavelength of light to be enhanced. In the organic EL element, the organic light emitting layer 13 is sandwiched between a pair of electrodes. Of these, one electrode is used as a mirror surface total reflection material, the other electrode is used as a translucent material for a dielectric mirror, and the thickness of the organic light emitting layer 13 is increased to the wavelength of light that is desired to be enhanced by R, G, and B light. Form together. As a result, the light emitted from the light emitter layer 17 repeats multiple reflections between the pair of electrodes and resonates, thereby being enhanced to a desired wavelength and output. Thereby, the directivity can be given to the light from the light-emitting body layer 17, and the luminous efficiency in the front can be improved. Thereby, light can be supplied to the color converter 7 more efficiently, and the front luminance can be increased. In addition, the emission spectrum can be adjusted by the interference effect. As a result, it is possible to control the spectrum so that the red and green phosphors can be excited more effectively, and to improve the color purity of the blue pixel.

  The phosphor layer 17 may be composed of only the organic light emitting material exemplified below, or may be composed of a combination of a light emitting dopant and a host material, and optionally, a hole transport material, an electron transport material, Additives (donor, acceptor, etc.) may be included, and these materials may be dispersed in a polymer material (binding resin) or an inorganic material. From the viewpoint of luminous efficiency and lifetime, those in which a luminescent dopant is dispersed in a host material are preferable.

  Examples of the organic light emitting material include known light emitting materials for organic EL. Such light-emitting materials are classified into low-molecular light-emitting materials, polymer light-emitting materials, and the like. Specific examples of these compounds are given below, but the present invention is not limited to these materials. The organic light emitting material may be classified into a fluorescent material, a phosphorescent material, and the like, and is preferably a phosphorescent material with high light emission efficiency from the viewpoint of reducing power consumption.

Here, although a specific compound is illustrated below, this invention is not limited to these compounds.
Examples of the low-molecular organic light-emitting material include aromatic dimethylidene compounds such as 4,4′-bis (2,2′-diphenylvinyl) -biphenyl (DPVBi), 5-methyl-2- [2- [4- ( Oxadiazole compounds such as 5-methyl-2-benzoxazolyl) phenyl] vinyl] benzoxazole, 3- (4-biphenylyl) -4-phenyl-5-t-butylphenyl-1,2,4- Examples include triazole derivatives such as triazole (TAZ), styrylbenzene compounds such as 1,4-bis (2-methylstyryl) benzene, and fluorescent organic materials such as fluorenone derivatives.

  Examples of the polymer light-emitting material include polyphenylene vinylene derivatives such as poly (2-decyloxy-1,4-phenylene) (DO-PPP), and polyspiro derivatives such as poly (9,9-dioctylfluorene) (PDAF). Can be mentioned.

Examples of the light-emitting dopant optionally contained in the light-emitting layer 17 include known dopant materials for organic EL elements. Examples of such dopant materials include fluorescent materials such as styryl derivatives, bis [(4,6-difluorophenyl) -pyridinato-N, C2 ′] picolinate iridium (III) (FIrpic), bis (4 ′, And phosphorescent organic metal complexes such as 6′-difluorophenylpolydinato) tetrakis (1-pyrazoyl) borateiridium (III) (FIr ₆ ).

  Examples of the host material when using the dopant include known host materials for organic EL elements. As such a host material, the above-described low molecular light emitting material, polymer light emitting material, 4,4′-bis (carbazole) biphenyl, 9,9-di (4-dicarbazole-benzyl) fluorene (CPF), 3 , 6-bis (triphenylsilyl) carbazole (mCP), carbazole derivatives such as (PCF), aniline derivatives such as 4- (diphenylphosphoyl) -N, N-diphenylaniline (HM-A1), 1,3- And fluorene derivatives such as bis (9-phenyl-9H-fluoren-9-yl) benzene (mDPFB) and 1,4-bis (9-phenyl-9H-fluoren-9-yl) benzene (pDPFB).

  The electric charge includes holes and electrons. For the purpose of more efficient injection of holes and electrons from the electrode and transport (injection) to the light emitter layer 17, a hole injection layer 19, a hole transport layer 18, an electron transport layer 15, and an electron injection layer 14 are used. Etc. are used. These layers may be composed only of the charge injecting and transporting materials exemplified below, and may optionally contain additives (donors, acceptors, etc.), and these materials are polymeric materials (binding). Resin) or an inorganic material.

  As the charge injecting and transporting material, known materials for organic EL elements and organic photoconductors can be used. Such charge injecting and transporting materials are classified into hole injecting and transporting materials and electron injecting and transporting materials. Specific examples of these compounds are given below, but the present invention is not limited to these materials.

Examples of the material for the hole injection layer and the hole transport layer include oxides such as vanadium oxide (V ₂ O ₅ ) and molybdenum oxide (MoO ₂ ), inorganic p-type semiconductor materials, porphyrin compounds, N, N′— Such as bis (3-methylphenyl) -N, N′-bis (phenyl) -benzidine (TPD), N, N′-di (naphthalen-1-yl) -N, N′-diphenyl-benzidine (NPD), etc. Low molecular weight materials such as aromatic tertiary amine compounds, hydrazone compounds, quinacridone compounds, styrylamine compounds, polyaniline (PANI), polyaniline-camphor sulfonic acid (PANI-CSA), 3,4-polyethylenedioxythiophene / polystyrene mon Phonate (PEDOT / PSS), poly (triphenylamine) derivative (Poly-TPD), polyvinylcarbazole Examples thereof include polymer materials such as (PVCz), poly (p-phenylene vinylene) (PPV), and poly (p-naphthalene vinylene) (PNV).

  From the viewpoint of more efficiently injecting and transporting holes from the anode 12, the material of the hole injection layer 19 has the highest occupied molecular orbital (HOMO) energy level than the material of the hole transport layer 18. Is preferably a low material. The material of the hole transport layer 18 is preferably a material having higher hole mobility than the material of the hole injection layer 19.

  In order to further improve hole injection / transport properties, it is preferable to dope an acceptor. As an acceptor, the well-known acceptor material for organic EL elements can be used. Although these specific compounds are illustrated below, this invention is not limited to these materials.

Acceptor materials include Au, Pt, W, Ir, POC ₁₃ , AsF ₆ , Cl, Br, I, vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₂ ) and other inorganic materials, TCNQ (7, 7 , 8,8, -tetracyanoquinodimethane), TCNQF ₄ (tetrafluorotetracyanoquinodimethane), TCNE (tetracyanoethylene), HCNB (hexacyanobutadiene), DDQ (dicyclodicyanobenzoquinone) and the like. And compounds having a nitro group such as TNF (trinitrofluorenone) and DNF (dinitrofluorenone), and organic materials such as fluoranyl, chloranil and bromanyl. Among these, compounds having a cyano group such as TCNQ, TCNQF ₄ , TCNE, HCNB, DDQ and the like are more preferable because they can increase the carrier concentration more effectively.

Examples of materials for the electron injection layer 14 and the electron transport layer 15 include inorganic materials that are n-type semiconductors, oxadiazole derivatives, triazole derivatives, thiopyrazine dioxide derivatives, benzoquinone derivatives, naphthoquinone derivatives, anthraquinone derivatives, diphenoquinone derivatives, Low molecular materials such as fluorenone derivatives and benzodifuran derivatives; polymer materials such as poly (oxadiazole) (Poly-OXZ) and polystyrene derivatives (PSS) are used. In particular, the electron injection layer 14 includes fluorides such as lithium fluoride (LiF) and barium fluoride (BaF ₂ ), and oxides such as lithium oxide (Li ₂ O).

  From the viewpoint of performing electron injection / transport from the cathode 11 more efficiently, the material of the electron injection layer 14 is a material having a higher energy level of the lowest unoccupied molecular orbital (LUMO) than the material of the electron transport layer 15. The material for the electron transport layer 15 is preferably a material having a higher electron mobility than the material for the electron injection layer 14.

  In order to further improve the electron injection efficiency and the electron transport property, the material of the electron injection layer 14 and the electron transport layer 15 is preferably doped with a donor. As a donor, the well-known donor material for organic EL elements can be used. Although these specific compounds are illustrated below, this invention is not limited to these materials.

  Donor materials include inorganic materials such as alkali metals, alkaline earth metals, rare earth elements, Al, Ag, Cu, and In, anilines, phenylenediamines, benzidines (N, N, N ′, N′-tetraphenyl) Benzidine, N, N′-bis- (3-methylphenyl) -N, N′-bis- (phenyl) -benzidine, N, N′-di (naphthalen-1-yl) -N, N′-diphenyl- Benzidine, etc.), triphenylamines (triphenylamine, 4,4 ', 4 "-tris (N, N-diphenyl-amino) -triphenylamine, 4,4', 4" -tris (N-3- Methylphenyl-N-phenyl-amino) -triphenylamine, 4,4 ′, 4 ″ -tris (N- (1-naphthyl) -N-phenyl-amino) -triphenylamine, etc.), triphenyldia Compounds having an aromatic tertiary amine skeleton such as N (N, N′-di- (4-methyl-phenyl) -N, N′-diphenyl-1,4-phenylenediamine), phenanthrene, pyrene, perylene Organic materials such as condensed polycyclic compounds such as anthracene, tetracene and pentacene (however, the condensed polycyclic compounds may have a substituent), TTF (tetrathiafulvalene), dibenzofuran, phenothiazine and carbazole. Of these, compounds having an aromatic tertiary amine skeleton, condensed polycyclic compounds, and alkali metals are more preferred because they can increase the carrier concentration more effectively.

  The organic light emitting layer 13 including the hole injection layer 19, the hole transport layer 18, the light emitter layer 17, the electron transport layer 15, the electron injection layer 14, and the like was prepared by dissolving and dispersing the materials of these layers in a solvent. Using the light emitting layer forming coating solution, spin coating method, dipping method, doctor blade method, discharge coating method, spray coating method and other coating methods, ink jet method, letterpress printing method, intaglio printing method, screen printing method, microgravure Known wet processes by printing methods such as coating methods, the above-mentioned materials are resistance heating vapor deposition, electron beam (EB) vapor deposition, molecular beam epitaxy (MBE), sputtering, organic vapor deposition (OVPD), etc. It can be formed by a known dry process or a laser transfer method. In addition, when forming the organic light emitting layer 13 by a wet process, the light emitting layer forming coating liquid may contain additives for adjusting the physical properties of the coating liquid, such as a leveling agent and a viscosity adjusting agent.

  The film thickness of each of the layers is, for example, about 1 to 1000 nm, but preferably 10 to 200 nm. If the film thickness is less than 10 nm, the physical properties (charge injection characteristics, transport characteristics, confinement characteristics) that are originally required cannot be obtained. In addition, pixel defects due to foreign matters such as dust may occur. On the other hand, if the film thickness exceeds 200 nm, the driving voltage increases due to the resistance component of the light emitting layer, leading to an increase in power consumption.

  Of the cathode 11 and the anode 12, the electrode from which light is extracted must transmit at least part of the light emitted from the light emitter layer 17. In the present embodiment, light emitted from the light emitter layer 17 is taken out from the anode 12 side. Note that the order of lamination may be reversed from that of the present embodiment, and light may be extracted from the cathode 11 and the anode 12 may reflect light.

As an electrode material for forming the cathode 11 and the anode 12, a known electrode material can be used. As an electrode material for forming the anode 12, gold (Au), platinum (Pt), nickel (Ni) having a work function of 4.5 eV or more from the viewpoint of efficiently injecting holes into the organic light emitting layer 13. ), And oxides (ITO) containing indium (In) and tin (Sn), oxides (SnO ₂ ) of tin (Sn), oxides containing indium (In) and zinc (Zn) ( IZO) and the like are listed as transparent electrode materials. As an electrode material for forming the cathode 11, lithium (Li), calcium (Ca), cerium (Ce) having a work function of 4.5 eV or less from the viewpoint of more efficiently injecting electrons into the organic light emitting layer 13. And metals such as barium (Ba) and aluminum (Al), or alloys such as Mg: Ag alloys and Li: Al alloys containing these metals.

  The sealing layer 21 seals the side surface of the light emitting unit 3. The sealing layer 21 can be formed using any insulating material. The insulating material may be either an organic material or an inorganic material.

  In an example of the light emitting unit 3 of the present embodiment, a glass substrate having a thickness of 0.7 mm is used as the first substrate 2 and the second substrate 4. As the anode 12, ITO having a film thickness of 100 nm is formed by sputtering. As the hole injection layer 19, 1,1-bis-di-4-tolylamino-phenyl-cyclohexane (TAPC) having a film thickness of 100 nm is formed by a resistance heating vapor deposition method. As the hole transport layer 18, N, N′-di-1-naphthyl-N, N′-diphenyl-1,1′-biphenyl-1,1′-biphenyl-4,4′-diamine having a film thickness of 40 nm (NPD) is formed by resistance heating vapor deposition. As the phosphor layer 17, a cyclopentadiene derivative (PPCP: 1,2,3,4,5-Pentaphenyl-1,3-cyclopentadiene) having a film thickness of 30 nm is resistance-heated under a deposition rate of 0.15 nm / second. It is formed by vapor deposition. As the hole blocking layer 16, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) having a thickness of 10 nm is formed. As the electron transport layer 15, tris (8-hydroxyquinoline) aluminum (Alq3) having a thickness of 30 nm is formed. As the electron injection layer 14, lithium fluoride (LiF) having a thickness of 0.5 nm is formed. As the cathode 11, a magnesium silver alloy having a film thickness of 1 nm is formed by a vacuum evaporation method by co-evaporation under conditions of an evaporation rate of 0.01 nm / second (magnesium) and 0.09 nm / second (silver).

  The dielectric layer 6 is formed on the second surface 2 b of the first substrate 2. The dielectric layer 6 is composed of a dielectric medium 9 including metal nanoparticles 5 such as silver. As the metal nanoparticles 5, those having a resonance wavelength in the wavelength range of light emitted from the light emitting portion 3 can be used. The metal nanoparticles 5 are disposed in a region corresponding to a red pixel region PR and a green pixel region PG described later, and are not disposed in a region corresponding to the blue pixel region PB.

The dielectric medium 9 is preferably one having high transparency in the visible range. For example, polystyrene, polyvinyl alcohol (PVA), 4,4 ′-[p-sulfonylbis (phenylenesulfanyl)] diphthalic anhydride (DPSDA), Polymethyl methacrylate (PMMA), epoxy resin, or the like is used. The relative dielectric constant ε of the dielectric medium 9 is ε = 2.20 to 2.40, ε = 2.56, ε = 3.24, ε = 3.50 to 4.50, and ε = 2.50. About 6.00. The dielectric medium 9 may be other than the above.
The dielectric medium 9 is preferably formed by a coating method, but may be formed by other means.

  Specific examples of the metal nanoparticles 5 include the following, but are not limited thereto. The metal nanoparticle 5 should just be what can induce a surface plasmon phenomenon. “Surface plasmon phenomenon” refers to a state in which electrons of fine particles such as metal nanoparticles 5 resonate with an electric field of light. The surface plasmon phenomenon is caused when light is incident from a material with a high refractive index to a material with a low refractive index below the critical angle and totally reflected and oozes into a material with a low refractive index, or the diameter is smaller than the wavelength of light. It is also excited when electrons such as metal particles resonate with near-field light (evanescent light) in the case of light entering from the opening when light enters the opening.

  Examples of the metal nanoparticles 5 include Au, Ag, Al, Pt, Cu, Mn, Mg, Ca, Li, Yb, Eu, Sr, Ba, Na, and two or more kinds of metals among these metals. An alloy selected and formed as appropriate, for example, Mg: Ag, Al: Li, Al: Ca, Mg: Li can be mentioned.

  The metal nanoparticles 5 are not limited to silver, and may be aluminum or indium as long as it has a resonance wavelength in the blue region. Moreover, it is necessary for each color conversion layer to efficiently absorb the enhanced electric field in the vicinity of the excited metal nanoparticles 5. Therefore, the thickness of the dielectric layer 6 and the average diameter of the metal nanoparticles 5 need to be substantially equal. Further, the smaller the particle size of the metal nanoparticles 5, the stronger the light absorption and the weaker the scattering. For this reason, the particle diameter of the metal nanoparticles 5 is preferably 20 nm or less. However, when the average diameter of the metal nanoparticles 5 is 10 nm, the thickness of the dielectric layer 6 is about 10 nm. In addition, it is preferable that the particle size variation is small. A particle size distribution of about 10 ± 2 nm is preferable for an average diameter of 10 nm, and a particle size distribution of about 20 ± 2 nm is preferable for an average diameter of 20 nm.

  The color conversion unit 7 includes two phosphor layers, a red phosphor layer 23 and a green phosphor layer 24, and one transmission layer 25. The red phosphor layer 23 is disposed in a region corresponding to the red pixel region PR. The green phosphor layer 24 is disposed in a region corresponding to the green pixel region PG. The transmissive layer 25 is disposed in a region corresponding to the blue pixel region PB. The transmissive layer 25 has a function of transmitting blue light and adjusting a light distribution state. In the light emitting device 1 of the present embodiment, the blue light emitted from the light emitting unit 3 enters the color conversion unit 7. Blue light incident on the red phosphor layer 23 is converted into red light and emitted. Blue light incident on the green phosphor layer 24 is converted into green light and emitted. The blue light incident on the transmissive layer 25 has its light distribution adjusted and is emitted as blue light.

  The red phosphor layer 23 and the green phosphor layer 24 may be composed only of the phosphor materials exemplified below, and may optionally contain additives and the like, and these materials are polymer materials (conjugates). Wear resin) or a structure dispersed in an inorganic material. A black matrix 26 is formed between two adjacent phosphor layers and between the phosphor layer and the transmission layer.

  As the phosphor material of the present embodiment, a known phosphor material can be used. Such phosphor materials are classified into organic phosphor materials and inorganic phosphor materials. Specific examples of these compounds are shown below, but the present invention is not limited to these materials.

  As an organic fluorescent material, as a fluorescent dye that converts blue excitation light into green light, coumarin dyes: 2,3,5,6-1H, 4H-tetrahydro-8-trifluoromethylquinolidine (9, 9a, 1-gh) Coumarin (coumarin 153), 3- (2'-benzothiazolyl) -7-diethylaminocoumarin (coumarin 6), 3- (2'-benzimidazolyl) -7-N, N-diethylaminocoumarin (coumarin 7) ), Naphthalimide dyes: basic yellow 51, solvent yellow 11, solvent yellow 116, and the like.

  As fluorescent dyes that convert blue excitation light into red light, cyanine dyes: 4-dicyanomethylene-2-methyl-6- (p-dimethylaminostyryl) -4H-pyran, pyridine dyes: 1-ethyl- 2- [4- (p-dimethylaminophenyl) -1,3-butadienyl] -pyridinium-perchlorate and rhodamine dyes: rhodamine B, rhodamine 6G, rhodamine 3B, rhodamine 101, rhodamine 110, basic violet 11, sulfo Rhodamine 101 etc. are mentioned.

Inorganic phosphor materials include (BaMg) Al ₁₆ O ₂₇ : Eu ²⁺ , Mn ²⁺ , Sr ₄ Al ₁₄ O ₂₅ : Eu ²⁺ , (SrBa) Al as phosphors that convert blue excitation light into green light. ₁₂ Si ₂ O ₈ : Eu ²⁺ , (BaMg) ₂ SiO ₄ : Eu ²⁺ , Y ₂ SiO ₅ : Ce ³⁺ , Tb ³⁺ , Sr ₂ P ₂ O ₇ -Sr ₂ B ₂ O ₅ : Eu ²⁺ , (BaCaMg) ₅ (PO ₄ ) 3Cl: Eu ²⁺ , Sr ₂ Si ₃ O ₈ -2SrCl ₂ : Eu ²⁺ , Zr ₂ SiO ₄ , MgAl ₁₁ O ₁₉ : Ce ³⁺ , Tb ³⁺ , Ba ₂ SiO ₄ : Eu ²⁺ , Sr ₂ SiO ₄ : Eu ²⁺ , (BaSr) SiO ₄ : Eu ^{2+ and the} like.

As phosphors that convert blue excitation light into red light, Y ₂ O ₂ S: Eu ³⁺ , YA ₁ O ₃ : Eu ³⁺ , Ca ₂ Y ₂ (SiO ₄ ) 6: Eu ³⁺ , LiY ₉ (SiO ₄ ) ₆ O ₂ : Eu ³⁺ , YVO ₄ : Eu ³⁺ , CaS: Eu ³⁺ , Gd ₂ O ₃ : Eu ³⁺ , Gd ₂ O ₂ S: Eu ³⁺ , Y (P, V) O ₄ : Eu ³⁺ , Mg ₄ GeO ₅ . ₅ F: Mn ⁴⁺ , Mg ₄ GeO ₆ : Mn ⁴⁺ , K ₅ Eu _2.5 (WO ₄ ) _6.25 , Na ₅ Eu _2.5 (WO ₄ ) _6.25 , K ₅ Eu _2.5 (MoO ₄ ) _6.25 , Na ₅ Eu _2.5 (MoO ₄ ) _{6.25, and the} like.

  Further, the red phosphor layer 23 and the green phosphor layer 24 are prepared by using a phosphor layer forming coating solution obtained by dissolving and dispersing the phosphor material and the resin material in a solvent, using a spin coating method, a dipping method, A known wet process using a coating method such as a doctor blade method, a discharge coating method, a spray coating method, an ink jet method, a relief printing method, an intaglio printing method, a screen printing method, a micro gravure coating method, etc. It may be formed by a known dry process such as resistance heating vapor deposition, electron beam (EB) vapor deposition, molecular beam epitaxy (MBE), sputtering, organic vapor deposition (OVPD), or a laser transfer method. it can.

  The film thicknesses of the red phosphor layer 23 and the green phosphor layer 24 are, for example, about 100 nm to 100 μm, and preferably 1 to 100 μm. By setting the film thickness to 100 nm or more, the blue light from the light emitting unit 3 can be sufficiently absorbed, and the effects of improving the light emission efficiency and improving the color purity by suppressing the color mixture of the blue light can be obtained. . Furthermore, in order to increase the absorption of light from the light emitting portion 3 and reduce blue transmitted light to the extent that the color purity is not adversely affected, the film thickness is preferably set to 1 μm or more. Further, when the film thickness is 100 μm, the blue light from the light emitting portion 3 is sufficiently absorbed, so that the consumption of the material can be suppressed while maintaining sufficient efficiency as compared with the case where the thickness is larger than this. Cost can be reduced. In this embodiment, in order to reduce the influence of self-absorption (re-absorption) by the phosphor, the red phosphor layer 23 and the green phosphor layer 24 are relatively thin in the range of 1 to 100 μm. The film thickness was 3 μm.

  Further, when forming the dielectric layer 6 of the present embodiment, for example, polyvinyl alcohol (PVA, PVA, an aqueous solution of silver nanoparticles (particle size: 20 nm, concentration: 0.02 mg / mL, manufactured by Sigma-Aldrich)) is used. 80% hydrolyzed, manufactured by Sigma-Aldrich) is dispersed by 10% by weight. This solution is spin-coated on the first substrate 2 at 6000 rpm for 30 seconds to form a thin film having a thickness of about 20 nm. Finally, the particles present in the blue pixel region PB are removed by means of FIB or electron beam exposure, thereby forming a dielectric layer containing silver nanoparticles.

When forming the color conversion unit 7, after forming the dielectric layer 6, the red phosphor layer 23, the green phosphor layer 24, and the transmission layer 25 having a width of 3 mm are formed by resistance heating vapor deposition. As a red dye used for the red phosphor layer 23, a Cresyl violet dye having an emission wavelength of 627 nm and an internal quantum yield of 0.95 is used. As a green pigment used for the green phosphor layer 24, coumarin 6 having an emission wavelength of 502 nm and an internal quantum yield of 1.00 is used. Silicon dioxide (SiO ₂ ) is used as the material of the transmission layer 25.
Further, a glass substrate having a thickness of 0.7 mm is used as the third substrate 8.

  In the present embodiment, the average distance from the surface of the color conversion unit 7 on the side in contact with the dielectric layer 6 to the metal nanoparticles 5 existing in the dielectric layer 6 is equal to or less than the average diameter of the metal nanoparticles 5. That is, the dielectric layer 6 is formed so that the film thickness thereof is thinner than the thickness in which two metal nanoparticles 5 are uniformly laminated. In other words, the dielectric layer 6 is formed to have a thickness such that the metal nanoparticles 5 do not overlap in two steps.

Hereinafter, the contents studied by the present inventors in order to achieve high brightness of the emitted light will be described.
In order to efficiently enhance the blue excitation light, the following two conditions must be satisfied.
The first condition is that the resonance wavelength band of the metal nanoparticles 5 and the absorption wavelength band of the blue excitation light overlap.
FIG. 2A shows a state where an enhanced electric field Een is formed in the vicinity of the metal nanoparticle 5 when the metal nanoparticle 5 is irradiated with the blue excitation light Lb of the incident electric field Eexc (λ) emitted from the light emitting unit 3. Is shown.

Here, the principle that the enhanced electric field Een is formed will be described below.
When the metal nanoparticle 5 is irradiated with the blue excitation light Lb of the incident electric field Eexc (λ) and the polarizability of the metal nanoparticle 5 is α (λ), the following equation (1) A dipole moment p (λ) represented by
p (λ) = α (λ) Eexc (λ) (1)

At this time, the dipole moment p (λ) generates its own electric field E (not shown) in the vicinity of the metal nanoparticles 5. The electric field E is a field that has the same direction as the incident electric field Eexc (λ) and abruptly attenuates with near 1 / r ³ dependence when the distance from the dipole is r (near field light). Eventually, the metal nanoparticles 5 feel the electric field E in addition to the incident electric field Eexc (λ) due to light from the outside, so that the incident electric field Eexc (λ) is enhanced and becomes an enhanced electric field Een (λ). is there.

Here, the average diameter D of the metal nanoparticles 5 is D = 20 nm. Further, silver nanoparticles are used as the metal nanoparticles 5.
FIG. 2B shows the wavelength dependence of the electric field enhancement intensity when the relative permittivity ε of the surrounding medium (dielectric medium) of the silver nanoparticles changes in the blue wavelength range (380 to 480 nm). The horizontal axis in FIG. 2B is the wavelength [nm], and the vertical axis is the electric field enhancement intensity. The electric field enhancement strength is expressed by | Een (λ) / Eexc (λ) | ² . From this, it can be seen that if the relative dielectric constant ε satisfies ε = 1.71 to 4.40, the resonance peak wavelength derived from silver nanoparticles exists in the blue wavelength range of 380 to 480 nm.

  In the present embodiment, the dielectric constant ε of the dielectric medium (polyvinyl alcohol) around the silver nanoparticles is ε = 2.56. FIG. 2C is a graph showing that a resonance peak wavelength of electric field enhancement in the vicinity of silver nanoparticles exists in the emission wavelength region of the blue light-emitting material when ε = 2.56. This means that when the blue excitation light Lb having a wavelength of 413 nm is incident on the metal nanoparticle 5, the electric field intensity at the same wavelength increases about 30 times.

Next, in order to efficiently cause color conversion using the enhanced excitation light, it is necessary to satisfy the second condition.
The second condition is that the fluorescent molecules 28 exist within the range covered by the enhanced electric field Een (λ) in the vicinity of the metal nanoparticles 5.

  FIG. 3A shows a calculation model for clarifying the range of the enhanced electric field Een (λ), which is the second condition. The electric field range determines the energy transfer (FRET) efficiency η by dipole-dipole coupling based on the following theoretical expressions (2) to (4). FIG. 3B shows the normalized enhanced electric field spectrum and the molar extinction coefficient of the fluorescent molecule in the following theoretical formula.

However,
R ₀ : Forster distance [nm]
r: Dipole-dipole distance [nm]
Q ₀ : Original fluorescence quantum yield n: Refractive index of dielectric medium (n = √ε: ε is relative dielectric constant)
N _A : Avogadro number [mol ⁻¹ ]
κ ² : Dipole orientation factor J: Overlap integral f _D (λ): Normalized enhanced electric field spectrum (see FIG. 3B)
ε _A (λ): molar extinction coefficient of fluorescent molecule [M ⁻¹ cm ⁻¹ ] (see FIG. 3B)

  4A is a diagram showing the distance between the metal nanoparticle 5 and the fluorescent molecule, and FIG. 4B is a graph showing the calculation result of the FRET efficiency η. In FIG. 4B, the horizontal axis indicates the distance r [nm] between the metal nanoparticles and the fluorescent molecule, and the vertical axis indicates the FRET efficiency η. As the fluorescent molecule, a rhodamine dye (Rh6G) used for the red phosphor layer was assumed. The distance r from the surface of the metal nanoparticle 5 to the fluorescent molecule is changed in four ways as r = 2, 5, 10, 14.6, and the positions separated by the distance r are the positions A, B, C, D, respectively. did.

  As shown in FIG. 4B, as the distance r from the surface of the metal nanoparticle 5 to the fluorescent molecule is increased to r = 2, 5, 10, 14.6, an enhanced electric field in the vicinity of the metal nanoparticle 5 is obtained. The intensity E (λ) decreased to E (λ = 413 nm) = 30, 19, 3, 1 (= incident electric field strength). When the distance r is 14.6, the enhanced electric field strength E is 1, which is equal to the incident electric field strength. Therefore, the condition that the enhanced electric field strength E is 1 or more (incident electric field strength or more) is that the distance from the surface of the metal nanoparticle 5 to the fluorescent molecule is within about 15 nm. Here, the average diameter of the metal nanoparticles 5 was set to 20 nm. Therefore, it is desirable that the distance from the surface of the metal nanoparticle 5 to the fluorescent molecule is smaller than the average diameter of the metal nanoparticle 5.

FIG. 4C shows the fluorescence spectrum of the rhodamine dye (Rh6G) at each position (A to D) reflecting the enhanced electric field Een.
The fluorescence intensity Iem (λ) is calculated according to the following equation (5).
Iem (λ) = ΦIen (λ) = Φ | Een (λ) / Eexc (λ) | ² · Iexc (λ) ∝ | Een (λ) / Eexc (λ) | ² (5)

  Thus, if the distance covered by the enhancement electric field Een (λ) is long, the fluorescence intensity Iem (λ) at that position increases. It should be noted that when excitation light enhancement is used, the FRET efficiency is high in the vicinity of the surface of the metal nanoparticle 5 and is not affected at all by the quenching by the metal nanoparticle 5. This is because the emission wavelength of the fluorescent molecule and the resonance wavelength of the metal nanoparticle 5 do not overlap. From this, it is considered that the use of excitation light enhancement rather than light emission enhancement leads to higher luminance emission.

Next, FRET efficiency was calculated not only for the red phosphor layer 23 using rhodamine dye (Rh6G) but also for the red phosphor layer 23 using another material. As another red fluorescent molecule, Cresyl violet perchlorate dye (CVP) was assumed.
FIG. 5A is a graph showing the calculation result of the FRET efficiency η.
The vertical axis of FIG. 5A is the FRET efficiency η, and the horizontal axis is the distance from the surface of the metal nanoparticle 5 to the fluorescent molecule. The solid line graph indicates the CVP dye, and the broken line graph indicates the rhodamine dye.

As shown in FIG. 5A, the distance effect of the enhanced electric field Een (λ) generated in the vicinity of the metal nanoparticles 5 is almost the same in both the red phosphor layer 23 and the red phosphor layer 23 using another material. It can be said.
However, in the equations (2), (3) and (4),
Q ₀ : Original red fluorescence quantum yield ε _A : Molar extinction coefficient [M ⁻¹ cm ⁻¹ ] of red fluorescent molecule (see FIG. 5B)

  As shown in FIG. 6A, the conventional light emitting device 101 includes the metal nanoparticles 5 in each of the red phosphor layer 23, the green phosphor layer 24, and the transmission layer 25. On the other hand, as shown in FIG. 6B, the light-emitting element 1 of the present embodiment is provided between the light-emitting portion 3 and each of the red phosphor layer 23, the green phosphor layer 24, and the transmission layer 25. A dielectric layer 6 containing metal nanoparticles 5 is formed. In the light emitting device 1 of the present embodiment, by providing the dielectric layer 6 containing the metal nanoparticles 5 separately from the phosphor layer, it is possible to obtain emitted light with higher brightness.

  FIG. 6C is a graph comparing the fluorescence intensities of the light-emitting element 1 of this embodiment and the conventional light-emitting element 101. In FIG. 6C, the horizontal axis represents the light absorption ratio [%] of the dielectric layer 6 containing the metal nanoparticles 5, and the vertical axis represents the fluorescence intensity [arbitrary unit] and the enhancement intensity. Since the conventional light emitting device 101 does not include the dielectric layer 6 containing the metal nanoparticles 5, the point where the light absorption ratio of the dielectric layer 6 is 0% indicates the fluorescence intensity of the conventional light emitting device 101. .

  For example, as shown in FIG. 6C, the increase in the fluorescence intensity in the light-emitting element 1 of the present embodiment is larger than 1 times the fluorescence intensity in the conventional light-emitting element 101 and is about 1.44 times. Thus, according to the light emitting element 1 of the present embodiment, it is possible to obtain emitted light with higher luminance.

  The basis for the calculation in FIG. 6C is as follows. For example, assuming that the excitation light intensity Iexc (λ = 413 nm) is 1 and the phosphor quantum yield Φ is 0.95, the fluorescence intensity Iem (λ = 551 nm) of the conventional light-emitting element 101 is Iem (fluorescence intensity). (Peak wavelength) = Φ × Iexc (peak wavelength of excitation light intensity) = 0.95 × 1 = 0.95. On the other hand, the fluorescence intensity Iem (λ = 551 nm) of the light-emitting element 1 of the present embodiment is the light emission intensity derived from the phosphor layer and the light emission intensity derived from the dielectric layer 6 containing the metal nanoparticles 5. Total. When the light absorption ratio of the dielectric layer 6 containing the metal nanoparticles 5 is 0.8 (80%), the emission intensity derived from the phosphor layer is 0.95 × 1 × (1-0.8) = 0. .19. The emission intensity derived from the dielectric layer 6 is 0.95 × (A / 3000) × 930 × 0.8 = 1.09. However, said A is represented by the following (6) Formula. Note that (A / 3000) indicates the ratio of the distance of energy transfer from the particle surface to the phosphor layer with respect to the phosphor layer thickness of 3000 nm.

  Therefore, the fluorescence intensity Iem (λ = 551 nm) of the light-emitting element 1 of the present embodiment is 0.19 + 1.09 = 1.28.

Briefly describing the magnification of the above enhancement,
(I) When the light absorption ratio of the dielectric layer 6 containing the metal nanoparticles 5 is 0%, that is, when the metal nanoparticles 5 are not present in the dielectric layer 6, the phosphor layer is thin. , A part of the excitation light is absorbed by the phosphor layer and the rest is transmitted. At this time, the intensity of fluorescence (λ = 551 nm) is 1 time.
(Ii) When the light absorption ratio of the dielectric layer 6 containing the metal nanoparticles 5 is 100%, that is, when the metal nanoparticles 5 are densely packed, all of the excitation light is absorbed by the dielectric layer 6. Will be. The increase in strength at that time is 1.44 times the maximum. However, in this case, it means that the distance between the particles is short enough to absorb all the excitation light, not the film, and any conditions may be used as long as surface plasmons localized by the particles are generated.

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS.
The basic configuration of the light emitting device of this embodiment is the same as that of the first embodiment, and the medium of the dielectric layer is different from that of the first embodiment.

  In the light emitting device of this embodiment, the dielectric layer is composed of a dielectric constant medium in which a plurality of silver nanoparticles are dispersed. As the dielectric constant medium, for example, a high relative dielectric constant polyimide containing sulfur having a higher relative dielectric constant than that of the dielectric medium used in the first embodiment and capable of realizing high transparency in the visible range is optimal. is there. The relative dielectric constant ε of the high relative dielectric constant polyimide is, for example, 3.24. At this time, as shown in FIG. 8A, the intensity of fluorescence increased 1.75 times.

  When forming this kind of dielectric layer, first, 4,4 ′-[p-sulfonylbis (phenylenesulfanyl)] diphthalic anhydride (DPSDA) in which a part of the sulfide bond is replaced with a sulfone bond is synthesized. To do. DPSDA is dispersed by 10% by weight in a silver nanoparticle aqueous solution (particle size 20 nm, concentration 0.02 mg / mL; manufactured by Sigma-Aldrich). Thereafter, polymerization is performed using 3SDA as an aromatic diamine, and this is spin-coated on a substrate at 6000 rpm for 30 seconds to form a thin film having a thickness of about 20 nm (relative dielectric constant ε≈3.24 of the host). Form. Here, the proportion of light absorbed by the dielectric layer containing silver nanoparticles is 80%, and the remaining 20% is the proportion of light absorbed by the phosphor layer, so that the silver nanoparticle is contained in the dielectric layer. The particles are dispersed. Finally, a silver nanoparticle-containing dielectric layer is formed by removing silver nanoparticles present in the blue pixel region by means of FIB or electron beam exposure.

According to FIG. 2 used when explaining the first embodiment, the electric field strength enhancement in the vicinity of the silver nanoparticles is as follows.
In the case of the first embodiment (ε = 2.56, wavelength λ = 413 nm),
| Een (λ) / Eexc (λ) | ² = 930
In the case of the second embodiment (ε = 3.24, wavelength λ = 445 nm),
| Een (λ) / Eexc (λ) | ² = 1273

FIG. 8B is a graph showing the relationship between the increase in fluorescence intensity and the light absorption ratio of the dielectric layer containing metal nanoparticles. The horizontal axis of the graph represents the light absorption ratio [%] of the dielectric layer containing metal nanoparticles, and the vertical axis represents the increase in fluorescence intensity.
As shown in FIG. 8B reflecting the effect of increasing the electric field intensity, the first embodiment (relative permittivity: ε = 2.56) and the second embodiment (relative permittivity: ε = 3. 24), in the light emitting device of the second embodiment using a dielectric medium having a high relative dielectric constant, the increase in fluorescence intensity is larger than that of the light emitting device of the first embodiment.

  According to the light emitting device of the present embodiment, the electric field strength is higher, and thus higher brightness fluorescence can be obtained. For example, the increase in the fluorescence intensity with respect to the conventional light emitting device is 1-1.44 times in the first embodiment, whereas it is 1-1.97 times in the present embodiment, which is the fluorescence intensity of the present embodiment. The increase in strength is greater than that in the first embodiment.

  Further, according to FIG. 8A, when polymethyl methacrylate (ε = 4.58) having a high relative dielectric constant is used as the dielectric medium, the fluorescence enhancement intensity is exactly 1.00 times. . On the other hand, when polystyrene having a low relative dielectric constant (ε = 2.20) was used, the fluorescence enhancement intensity was 1.00 times or more.

  Even if there is no resonance peak wavelength in the blue wavelength range, if the relative dielectric constant ε = 4.58, the electric field enhancement at the wavelength of 480 nm is reduced by about 50% of the peak value. The increase in strength was 1.00 times. However, when the relative dielectric constant ε was further increased, for example, when the relative dielectric constant ε was 4.59, the fluorescence enhancement when the particles were dispersed in the dielectric layer decreased to 0.97 times. On the other hand, when the relative dielectric constant ε = 1.70, the fluorescence enhancement when the particles were dispersed in the dielectric layer was also reduced to 0.99 times.

From the above, when the relative dielectric constant ε of the dielectric medium used for the dielectric layer satisfies ε = 1.71 to 4.58, the fluorescence enhancement is always 1.00 times or more as an effect of particle dispersion. Become.
This is because the excitation light directly irradiates the particle, a part of the energy moves to the molecule and emits light, and the amount of light that passes through the particle and irradiates and emits light to the phosphor layer. It means that the fluorescence intensity increases.

[Third Embodiment]
Hereinafter, a third embodiment of the present invention will be described with reference to FIGS.
The basic configuration of the light emitting device of this embodiment is the same as that of the first embodiment, and the shape of the metal nanoparticles is different from that of the first embodiment.
FIG. 9 is a cross-sectional view showing the light emitting device of the third embodiment.
9, the same code | symbol is attached | subjected to the same component as FIG. 1 used in 1st Embodiment, and detailed description is abbreviate | omitted.

  In the light emitting devices of the first and second embodiments, the shape of the metal nanoparticles contained in the dielectric layer was spherical. On the other hand, in the light emitting element 31 of the third embodiment, the shape of the metal nanoparticles 33 contained in the dielectric layer 32 is a rod (rod). Therefore, in the present embodiment, hereinafter, the metal nanoparticles are referred to as metal nanorods 33. In the present embodiment, as shown in FIG. 9, the plurality of metal nanorods 33 are arranged inside the dielectric layer 32 so that the major axis direction of the metal nanorods 33 faces the thickness direction of the dielectric layer 32. . In the present embodiment, it is desirable that the plurality of metal nanorods 33 are arranged in one direction as described above, but they may be arranged at random.

  As shown in FIG. 10, in the vicinity of the metal nanorod 33, an enhanced electric field Een (λ) is generated along the long axis direction of the metal nanorod 33. The electric field strength derived from the long axis of the metal nanorod 33 is larger on the longer wavelength side. Therefore, in the light emitting unit 3 of the present embodiment, a blue light emitting material having an emission peak wavelength at a wavelength of 480 to 500 nm is used.

Hereinafter, a method for producing a blue light emitting material used in the present embodiment will be described.
Instead of the cyclopentadiene derivative (PPCP) used in the first embodiment and the second embodiment, 1,4-bis-triphenylsilyl-benzene (UGH-2) (host material) and bis [(4,6- Difluorophenyl) -pyridinato-N, C2 ′] picolinate iridium (III) (FIrpic, emission wavelength 496 nm) (blue phosphorescent dopant), with respective deposition rates of 1.5 Å / sec, 0.2 Å / sec The organic light emitting layer is formed by co-evaporation under the following conditions and forming a film with a thickness of 30 nm.

As shown in FIG. 10, the length of the metal nanorods 33 in the major axis direction is a, and the length of the metal nanorods 33 in the minor axis direction is b. At this time, the electric field strength increase | Een (λ) / Eexc (λ) | ² in the vicinity of the metal nanorod 33 is
| Een (λ) / Eexc (λ) | ² = | 1 + 2 × α _nanorod (λ) / 4πab ² |
(α _nanorod (λ): Polarizability derived from the major axis of metal nanorods)
It is represented by

FIG. 11A is a graph showing the wavelength dependence of the enhancement of the electric field strength in the vicinity of the metal nanorod 33. The horizontal axis of the graph is the wavelength [nm], and the vertical axis is the electric field strength increase.
As shown in FIG. 11A, when the aspect ratio R is R = a / b, in the first embodiment (R = 1.0) using spherical metal nanoparticles,
| Een (λ) / Eexc (λ) | ² = 930
In the case of this embodiment (R=1.6@λ=489 nm) using metal nanorods,
| Een (λ) / Eexc (λ) | ² ≈ 2164
It becomes.

As described above, when the first embodiment (R = 1.0) and the present embodiment (R = 1.6) are compared, the dielectric layer 32 of the present embodiment having a high aspect ratio of the metal nanoparticles has the electric field strength. Is greater than that of the first embodiment. This is because the _{depolarization} field coefficient L in α _nanorod (λ) takes a smaller value (L <1/3) than that in the case of metal _nanospheres (L = 1/3). That is, the smaller the counter electric field coefficient L, the greater the increase in electric field strength. Thereby, since the value of polarizability becomes α _nanosphere (λ) <α _nanorod (λ), the electric field enhancement strength derived from the long axis of the metal nanorod is higher.

According to the light emitting element 31 of the present embodiment, since the electric field strength is increased by including the metal nanorods 33 in the dielectric layer 32, fluorescence with higher luminance can be obtained.
FIG. 11B shows a graph showing the relationship between the increase in fluorescence intensity and the light absorption ratio of the dielectric layer containing metal nanorods. The horizontal axis of the graph is the light absorption ratio [%] of the dielectric layer, and the vertical axis is the increase in fluorescence intensity.
The increase in the fluorescence intensity with respect to the conventional light emitting device is 1-1.44 times in the first embodiment, whereas it is 1-3.34 times in the present embodiment. Thus, the light emitting element 31 of the present embodiment has a high fluorescence intensity enhancement.

[Fourth Embodiment]
Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS.
The basic configuration of the light emitting device of this embodiment is the same as that of the first embodiment, and the emission color of the light emitting unit is different from that of the first embodiment.
FIG. 12 is a cross-sectional view showing the light emitting device of the fourth embodiment.
In FIG. 12, the same components as those in FIG. 1 used in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the light emitting elements of the first to third embodiments, the light emitted from the light emitting unit is blue light. On the other hand, in the light emitting element 41 of the fourth embodiment, the light emitted from the light emitting unit 42 is blue-green light. That is, the emission spectrum of the light emitting unit 42 of the present embodiment includes a longer wavelength component than the emission spectra of the light emitting units of the first to third embodiments. Furthermore, in the present embodiment, as shown in FIG. 12, light on the longer wavelength side than the blue-green wavelength region is cut above the transmission layer 25 corresponding to the blue pixel region PB, and light in the blue wavelength region is transmitted. The color filter 43 is provided. The color filter 43 may be formed with a metal hole array structure. However, the present invention is not limited to this, and a color filter formed of a dielectric multilayer film may be used. The configurations of the red pixel region PR and the green pixel region PG are the same as in the first embodiment.

  An example of an emission spectrum of the light emitting unit 42 in the light emitting element 41 of the present embodiment is shown in FIG. In this way, light in the blue-green wavelength region, that is, light having a wavelength of 480 to 500 nm or more out of the wavelength region of the light emitted from the light emitting unit 42 is almost cut by the color filter 43. As a result, as shown in FIG. 13B, only light in the blue wavelength region, that is, light having a wavelength of 380 to 480 nm is emitted from the blue pixel region PB.

  According to the light emitting element 41 of the present embodiment, light of the three primary colors R, G, and B can be emitted, and the range of the color triangle is widened. Thereby, a color corresponding to a wider color gamut can be expressed.

[Fifth Embodiment]
Hereinafter, a fifth embodiment of the present invention will be described with reference to FIGS. 14 and 15.
The basic configuration of the light emitting device of this embodiment is the same as that of the first embodiment, and the configuration of the color conversion unit is different from that of the first embodiment.
FIG. 14 is a cross-sectional view showing the light emitting device of the fourth embodiment.
In FIG. 14, the same components as those in FIG. 1 used in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the light-emitting elements of the first to fourth embodiments, metal nanoparticles are contained inside the dielectric layer, and no metal nanoparticles are contained inside the color conversion part. On the other hand, as shown in FIG. 14, in the light emitting element 51 of the fifth embodiment, in addition to the inside of the dielectric layer 6, the red phosphor layer 23 and the green phosphor layer 24 constituting the color conversion unit 7. The metal nanoparticles 5 are also contained in the inside. The metal nanoparticles 5 are not contained inside the transmission layer 25.

  In the case of the present embodiment, as shown in FIG. 15, since the metal nanoparticles 5 are also contained inside the red phosphor layer 23 and the green phosphor layer 24, the vicinity of the metal nanoparticles 5 generated by the blue excitation light. The enhanced electric field Een (λ) can be efficiently absorbed by the fluorescent molecules. Further, since the fluorescence is enhanced by enhancing the excitation light, the fluorescence emitted inside the red phosphor layer 23 and the green phosphor layer 24 is not reabsorbed by the metal nanoparticles 5 and the efficiency is high.

  According to the light emitting element 51 of the present embodiment, it is possible to realize a light emitting element with higher brightness as compared with the first embodiment. For example, the increase in fluorescence intensity with respect to the conventional light emitting device is 1 to 1.44 times in the first embodiment, whereas it is about 1.44 to 5 times in the present embodiment. The increase in strength is high.

[Sixth Embodiment]
Hereinafter, a sixth embodiment of the present invention will be described with reference to FIG.
The basic configuration of the light emitting device of this embodiment is the same as that of the fifth embodiment, and the form of the metal nanoparticles is different from that of the fifth embodiment.

  In the light emitting element 51 of the fifth embodiment, in the color conversion part, for example, the red phosphor layer 23, the fluorescent molecules 28 and the metal nanoparticles 5 are evenly mixed as shown in FIG. On the other hand, in the light emitting element 61 of the present embodiment, as shown in FIG. 16B, the periphery of the metal nanoparticles 5 is covered with a dielectric layer 62 containing the fluorescent molecules 28. The dielectric layer 62 covering the periphery of the metal nanoparticles 5 is composed of, for example, a silica layer having a thickness of several nm.

  When the resonance wavelength of the metal nanoparticle 5 matches the wavelength of the excitation light (absorption wavelength of the fluorescent molecule), the excitation light is enhanced in electric field by plasmons in the vicinity of the metal nanoparticle 5. That is, excitation light enhancement occurs. In this case, it is considered that quenching by metal does not occur. As the distance from the surface of the metal nanoparticle 5 increases, the range in which the enhanced electric field strength is exerted becomes smaller. Therefore, it is necessary to arrange the fluorescent molecules 28 within the range in which the enhanced electric field strength is exerted.

  In that respect, according to the light emitting element 61 of the present embodiment, since the periphery of the metal nanoparticles 5 is covered with the dielectric layer 62 containing the fluorescent molecules 28, the fluorescent light is sufficiently close to the metal nanoparticles 5. Molecule 28 is present. Thereby, light emission is efficiently generated with a small amount of fluorescent molecules 28. That is, since there is no fluorescent molecule 28 that does not contribute to fluorescence enhancement, higher brightness fluorescence can be obtained even with the same thickness.

[Other components]
Not only in the fourth embodiment but also in other embodiments, a color filter may be provided between the third substrate 8 on the light extraction side and the color conversion unit 7. By using the color filter, the color purity of the red pixel region, the green pixel region, and the blue pixel region can be increased, and the color reproduction range of the light emitting element can be expanded. In this case, the red color filter disposed on the red phosphor layer and the green color filter disposed on the green phosphor layer absorb the blue component and the ultraviolet component of the external light. Light emission can be reduced or prevented. As a result, a decrease in contrast can be reduced or prevented.

  Further, a polarizing plate may be provided on the light emission side of the third substrate 8. As the polarizing plate, a combination of a linear polarizing plate and a λ / 4 plate can be used. By providing the polarizing plate, it is possible to prevent external light reflection from the electrode of the light emitting element and external light reflection on the surface of the third substrate. As a result, the contrast of the display device can be improved.

  In addition, in said embodiment, although the case where the light emission part 3 was an organic electroluminescent light emitting layer was demonstrated, it is not restricted to this. For example, a light emitting diode (LED) such as a blue light emitting diode may be employed as the light emitting unit. In addition, when an LED is employed, blocking and transmission of light emitted by the liquid crystal may be controlled.

  The light-emitting element of the present invention can be used for various display devices.

  DESCRIPTION OF SYMBOLS 1,31,41,51,61 ... Light emitting element, 3,42 ... Light emission part, 5 ... Metal nanoparticle, 6, 32, 62 ... Dielectric layer, 7 ... Color conversion part, 9 ... Dielectric medium, 23 ... Red phosphor layer, 24 ... green phosphor layer, 25 ... transmission layer, 33 ... metal nanorod, 43 ... color filter.

Claims (8)

A light emitting unit for emitting excitation light;
A color conversion unit that is provided on the light emission side of the light emitting unit, includes a phosphor that generates fluorescence when irradiated with the excitation light, and the phosphor converts the color of light from the light emitting unit by emitting fluorescence;
A dielectric layer made of a dielectric medium containing a plurality of metal nanoparticles that is provided between the light emitting unit and the color conversion unit and expresses a surface plasmon phenomenon;
With
The average distance from the surface of the color conversion portion on the side in contact with the dielectric layer to the metal nanoparticles present in the dielectric layer is equal to or less than the average diameter of the metal nanoparticles. .   The light emitting device according to claim 1, wherein the light emitted from the light emitting unit is blue light. The color conversion unit includes a phosphor layer that emits color light other than blue light as the fluorescence, and a light transmission layer that transmits blue light emitted from the light emitting unit,
Of the color conversion part, the metal nanoparticles are contained in the dielectric layer corresponding to the formation region of the phosphor layer, and the metal nanoparticles are included in the dielectric layer corresponding to the formation region of the light transmission layer. The light-emitting element according to claim 2, wherein the light-emitting element is not contained.   4. The light emitting device according to claim 1, wherein a relative dielectric constant of the dielectric medium is 1.71 or more and 4.58 or less. 5.   The metal nanoparticles have a rod-like shape and are oriented so that the major axis direction of the metal nanoparticles is substantially directed to the thickness direction of the dielectric layer. Item 5. The light emitting device according to any one of Items 4 to 4.   The light emitting device according to claim 1, wherein a color filter is provided on a light emission side of the color conversion unit.   The light emitting device according to any one of claims 1 to 6, wherein a plurality of metal nanoparticles that express a surface plasmon phenomenon are contained inside the color conversion unit.   The light emitting device according to claim 7, wherein the metal nanoparticles are covered with a dielectric containing a fluorescent molecule.