JP2006236924A - Inorganic dispersion type electroluminescent element and luminescent element system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL element capable of providing high-luminance luminescence and high luminous efficiency. <P>SOLUTION: This dispersion type electroluminescent element has a phosphor layer containing phosphor particles between a pair of facing electrodes at least one of which is transparent. The electroluminescent element is characterized by that the surface resistivity of a transparent conductive film in the at least one transparent electrode is 0.5-80 Ω/SQUARE; the average particle size of the phosphor particles is 12-22 μm; and the variation coefficient of the particle size is not greater than 35%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electroluminescence element and a light-emitting element system having a large area, high luminance, and high efficiency.

  Electroluminescent elements (hereinafter also referred to as EL elements) are inorganic electro-mechanical elements such as a particle-dispersed element in which phosphor particles are dispersed in a high dielectric material, and a thin-film element in which a phosphor thin film is sandwiched between dielectric layers. It is roughly classified into a luminescence element and an organic electroluminescence element. The present invention mainly relates to a particle-dispersed inorganic electroluminescence device.

  In the dispersion type, a light emitting layer comprising a phosphor powder in a high dielectric polymer such as a fluorine rubber or a polymer having a cyano group is placed between a pair of conductive electrode sheets, at least one of which is light transmissive. Element. Further, in order to prevent dielectric breakdown, it is a normal form that a dielectric layer comprising a ferroelectric powder such as barium titanate is placed in a high dielectric polymer.

Particle dispersive elements do not use a high-temperature process when configuring the elements, so that a flexible material structure using plastic as a substrate is possible, and they are manufactured in a relatively simple process and at a low cost without using a vacuum device. It is possible to adjust the emission color of the element by mixing a plurality of phosphor particles having different emission colors, and is applied to backlights and display elements. However, since the light emission luminance is low and the light emission lifetime is short, many of them have a limited application range. Also, the luminous efficiency is low, and the problem of heat generation and increased power consumption became obvious when the luminous brightness was increased. Therefore, further improvement in light emission luminance and light emission efficiency has been desired.
Also, in reality, when the area is increased or when emitting light with high brightness, it is easy to cause deterioration or failure due to heat generation. In principle, both high brightness and large area are compatible, even though the area can be increased. I did not.

For conventional electroluminescence elements, transparent conductive films having a surface resistivity of 100Ω / □ to 300Ω / □ have been used. In order to emit light uniformly over a large area, lowering the resistance of the transparent conductive film is expected in principle. However, in practice, it is necessary to coat the transparent conductive material thickly, resulting in a decrease in light transmittance. It was not adopted because of high cost.
In addition, there are many conventional techniques related to the transparent conductive film, which are described in, for example, Non-Patent Document 1, Patent Document 1 and the like. It was not possible to obtain a sufficiently high brightness and high efficiency simply by reducing the power.

On the other hand, phosphor powders that are usually used are generally those based on ZnS.
Examples of the different types of metal dopants in the electroluminescent phosphor include at least one kind of ions selected from copper, manganese, and rare earth elements, which are usually used as a light emitting center as an activator, and chlorine, bromine, iodine, and aluminum. These have a function of providing an emission center or forming copper sulfide like copper to generate electrons (holes).

The average particle size of the phosphors used in these electroluminescent devices is usually about 24 μm to 30 μm, and the reason for not using small particles is that the luminance is reduced by decreasing the size and the durability is lowered. This is well known in the art.
Patent Document 2 describes that a high-brightness electroluminescence device can be provided by maintaining the relationship between the size and distribution of the phosphor particles and the thickness of the phosphor layer at a certain condition. In this method, It was not sufficient to cause the electroluminescence element to emit light with high luminance. Further, even when the luminance was increased, the luminance half-life was extremely shortened, and when the area was increased, the luminance was lowered.

Furthermore, as an example of providing a layer between a light emitting particle-containing layer and a transparent electrode in a dispersion type EL element, there is known an improvement in adhesion between layers (Patent Document 3), but there is any description about efficiency. No. In addition, there is known a method in which an intermediate layer is formed using a thermoplastic resin having a softening point of 200 ° C. or lower (Patent Document 4). However, in this method, conditions for generating high luminance (for example, a frequency of 800 Hz or more and a voltage of 120 V are used). In the above driving), the effect was not sufficient.
Published by Toray Research Center "Current Status and Future of Electromagnetic Shielding Materials" Japanese Patent Laid-Open No. 9-147639 Japanese Patent Publication No. 7-85636 JP-A-8-288066 Japanese Patent Laid-Open No. 10-134963

  As described above, in the conventional EL element technology, sufficient brightness and efficiency cannot be obtained. In particular, the larger the display advertisement is, the greater the advertising effect is. Therefore, the display advertisement is required to be used in a large format as a backlight light source for the display advertisement. However, since the conventional EL element has low luminance, its application to these elements is limited. On the other hand, large planar light sources using fluorescent tubes, cold cathode tubes, etc. are used, but these are heavy, cannot be carried, require a large installation space, consume a lot of power, and have a large power consumption. There were major limitations.

  Furthermore, another problem in the case of using inorganic EL for these exhibition advertisements and indirect illumination is that red light emission has not been sufficient in the past. Zinc sulfide phosphors using Mn emit orange light and are therefore often used in white light-emitting electroluminescent devices. A solid dispersion of rhodamine B-based fluorescent dyes has often been used in combination with a zinc sulfide phosphor in order to obtain white light emission. However, since these emission peaks are almost 590 nm or less, there are few light emitting components of 610 nm or more for showing sufficient color rendering properties, and only an electroluminescent material having extremely low color rendering properties can be obtained.

Various power source technologies are known as a means for compensating for a decrease in luminance due to degradation of the electroluminescence element, but most of these are related to a light emitting system of a small size and a low power, particularly 0.1 m ² or more. Is a large-scale power source that emits light from a large panel of 0.5 m ² or more.

As described above, an object of the present invention is to provide an EL device capable of realizing high luminance light emission and high light emission efficiency. In particular, an EL device having a large area of 0.1 m ² or more can emit light with high luminance and high efficiency. Realizing the above is a further challenge.

The above-described problems of the present invention have been achieved by the following items specifying the present invention and preferred embodiments thereof.
(1) In a dispersive electroluminescence device having a phosphor layer containing phosphor particles between a pair of opposing electrodes, at least one of which is transparent, the surface resistivity of the transparent conductive film in the at least one transparent electrode The electroluminescence device is characterized in that the average particle size of the phosphor particles is from 12 μm to 22 μm, and the variation coefficient of the particle size is 35% or less.
(2) In the above (1), an electroluminescent element characterized by having an insulating intermediate layer made of an organic substance between the transparent conductive film of the transparent conductive film and the phosphor layer.
(3) The electroluminescent device according to (1) or (2), wherein the phosphor layer has a thickness of 30 μm or more and 60 μm or less.
(4) In any one of the above (1) to (3), the electroluminescence device has a peak of emission intensity at 600 nm or more, emits white light, and is used at an initial luminance of 400 cd / m ² or more.

(5) In any one of the above (1) to (4), the phosphor particles contain at least one of Au, Mo, W, and Pt.
(6) In any one of the above (1) to (5), the phosphor particles contain Au, and further contain at least one metal ion selected from Mo, Bi, Sb, W, Pt and a group 8 metal. An electroluminescent device characterized by that.
(7) In any one of the above (1) to (6), the light emitting area is 0.1 m ² or more.
(8) In the light emitting element system using the electroluminescent element according to any one of (1) to (7), a power source for driving the electroluminescent element detects a current and keeps it constant A light-emitting element system comprising:

According to the present invention, by combining a transparent conductive film having a certain resistance value or less and a phosphor having a small particle size, it is possible to realize a large efficiency improvement that cannot be conventionally expected, particularly a high luminance region of 300 cd / m ² or more. It is what I found.
According to the study by the present inventors, in the small-sized particles, the fine particles of the center size or less often cause a large number of contact points with the transparent conductive film, and this conductive portion becomes an extra current and becomes a system of the system. It is estimated that the efficiency will be reduced and heat will be generated. These contact points are estimated not only to promote the deterioration of particles due to heat generation, but also to cause degradation and destruction of the transparent conductive film layer itself, leading to a decrease in device performance, particularly a decrease in luminance.
Regarding the light emission mechanism of the electroluminescent phosphor, there are many things specified in the prior art, but there is little disclosed about means for increasing the efficiency of the radiation emission process, or it is not related to the essential mechanism, Many have been included in the conventional knowledge as disclosure of the range of adjustment.

The present inventors further improve the efficiency of electroluminescence by modulating the light emission process and improving the efficiency of radiative recombination emission, rather than the dopant technology that provides conventional emission centers and electron sources. I found. By using these technologies and intermediate layer technologies, optimizing phosphor layer thickness design, selecting phosphor particle size and distribution, and designing transparent conductive films, high brightness in a large area device, which was previously unpredictable -A means for realizing high efficiency can be provided.
Furthermore, as a result of intensive studies, the present inventors, in the case of a power source for driving an electroluminescence element of 80 W or more, detect current and compensate the current with voltage and frequency as a guarantee of luminance accompanying element degradation. Thus, it has been found that it is most preferable to supplement power and suppress a decrease in luminance.

  The EL element of the present invention basically has a configuration in which a phosphor layer (also referred to as “light emitting layer”) is sandwiched between a pair of opposing electrodes, at least one of which is transparent. Moreover, it is preferable to adjoin a dielectric layer between a light emitting layer and an electrode.

(Transparent conductive film)
The resistance value of the transparent conductive film preferably used in the present invention is preferably from 0.5Ω / □ to 80Ω / □. In particular, 1Ω / □ to 30Ω / □ is preferable.
The surface resistivity of the transparent conductive film can be measured according to the method described in JIS K6911.

Transparent conductive film is vapor-deposited and coated with transparent conductive materials such as indium / tin oxide (ITO), tin oxide, and zinc oxide on transparent films (supports) such as polyethylene terephthalate and triacetyl cellulose. It is obtained by depositing and forming a film by a method such as printing to form a transparent conductive film.
The method for preparing the transparent conductive film may be a gas phase method such as sputtering or vacuum deposition. Paste ITO or the like may be formed by coating or screen printing, or the film may be heated to form a film.

In the EL device of the present invention, any transparent electrode material that is generally used is used for the transparent conductive film. Examples thereof include oxides such as tin-doped tin oxide, antimony-doped tin oxide and zinc-doped tin oxide, multilayer structures in which a silver thin film is sandwiched between high refractive index layers, and conjugated polymers such as polyaniline and polypyrrole.
In the case where the resistance cannot be sufficiently reduced by these single techniques, it is preferable to improve the conductivity by arranging, for example, a comb-shaped or grid-shaped metal or striped metal fine wire. Copper, silver, and aluminum are preferably used as the fine wires of the metal or alloy. The thickness of the fine metal wire is arbitrary, but is preferably between about 0.5 μm and 20 μm. The fine metal wires are preferably arranged at a pitch of 50 μm to 400 μm, and a pitch of 100 μm to 300 μm is particularly preferable. Although the light transmittance is reduced by arranging the fine metal wires, it is important that this reduction is as small as possible, and it is preferable to secure a transmittance of 80% or more and less than 100.

  For the fine metal wires, the mesh may be bonded to the transparent conductive film, or a metal oxide or the like may be applied and vapor-deposited on the fine metal wires previously formed on the film by mask vapor deposition or etching. Moreover, you may form said metal fine wire on the metal oxide thin film formed previously.

Although this is a different method, instead of a thin metal wire, a thin metal film having an average thickness of 100 nm or less can be laminated with a metal oxide to form a transparent conductive film suitable for the present invention. The metal to be used is preferably a metal having high corrosion resistance such as Au, In, Sn, Cu, and Ni, and excellent in ductility, but is not particularly limited thereto.
These multilayer films preferably realize high light transmittance, preferably have a light transmittance of 70% or more, and particularly preferably have a light transmittance of 80% or more. The wavelength that defines the light transmittance is 550 nm.

(Phosphor particles)
The electroluminescent phosphor particles used in the present invention have an average sphere equivalent diameter of 12 μm to 22 μm, preferably 12 m to 20 μm, more preferably 14 μm to 18 μm. The variation coefficient of the sphere equivalent diameter is 35% or less, preferably 5% or more and 30% or less. As the preparation method, a calcination method, a urea melting method, a spray pyrolysis method, or a hydrothermal synthesis method can be preferably used.
As a specific method for controlling the particle size and distribution, for example, in the firing method, it depends on the method of using the flux and the sieve. In the hydrothermal synthesis method, renucleation can be prevented by controlling the degree of supersaturation, and the size can be increased or decreased while keeping the particle size distribution narrow.

  For the average size and variation coefficient of the phosphor particles of the present invention, for example, a method using laser scattering such as a laser diffraction / scattering particle size distribution measuring apparatus LA-920 manufactured by Horiba, Ltd. can be used. Here, the average particle diameter refers to the median diameter.

  The synthesized particles preferably have a multiple twin structure. In the case of zinc sulfide, the plane spacing of multiple twins (stacking fault structure) is preferably 1 nm to 10 nm, more preferably 2 nm to 5 nm.

The phosphor fine particles usable in the present invention can be formed by a firing method (solid phase method) widely used in the industry. For example, in the case of zinc sulfide, a fine particle powder (usually called raw powder) of 10 nm to 50 nm is prepared by a liquid phase method, and this is used as a primary particle, and an impurity called an activator is mixed therein together with a flux. First baking is performed in a crucible at a high temperature of 900 ° C. to 1300 ° C. for 30 minutes to 10 hours to obtain particles.
The intermediate phosphor powder obtained by the first firing is repeatedly washed with ion exchange water to remove alkali metal or alkaline earth metal, excess activator and coactivator.
Next, second baking is applied to the obtained intermediate phosphor powder. In the second baking, heating (annealing) is performed at a temperature lower than that of the first baking at 500 to 800 ° C. and for a short time of 30 minutes to 3 hours.
These firings cause many stacking faults in the phosphor particles, but the conditions of the first firing and the second firing are appropriately set so that fine particles and more stacking faults are included in the phosphor particles. It is preferable to select.

  Further, by applying an impact force in a certain range to the first fired product, the density of stacking faults can be greatly increased without destroying the particles. Methods for applying impact force include methods of contacting and mixing intermediate phosphor particles, methods of mixing and mixing spheres such as alumina (ball mill), methods of accelerating and colliding particles, methods of irradiating ultrasonic waves, hydrostatic pressure A method of using can be preferably used.

By these methods, it is possible to form particles having 10 or more stacking faults at intervals of 5 nm or less. As a method for evaluating the frequency, when the particles were ground with a mortar and crushed into pieces having a thickness of approximately 0.2 μm or less, and observed with an electron microscope with an acceleration voltage of 200 KV, 10 or more layers were laminated at intervals of 5 nm or less. It can be evaluated by the frequency of debris particles containing defects. Of course, particles having a thickness of less than 0.2 μm need not be crushed and are observed as they are.
The particles of the present invention preferably have a frequency exceeding 50%, more preferably more than 70%. The higher the frequency, the better. The smaller the gap between stacking faults, the better.

  Thereafter, the intermediate phosphor is etched with an acid such as HCl to remove the metal oxide adhering to the surface, and the copper sulfide adhering to the surface is removed by washing with KCN. Subsequently, the intermediate phosphor can be dried to obtain an EL phosphor.

As described in Japanese Patent No. 2756044 and US Pat. No. 6,458,512, the phosphor particles are covered with a non-light emitting shell layer composed of a metal oxide or metal nitride of 0.01 μm or more, thereby being waterproof. It is preferable to impart water resistance and water resistance.
Further, as described in WO02 / 080626, a technique of increasing the light extraction efficiency can be preferably used by forming a double structure including a core portion including a light emission center and a non-light emitting shell portion.

More preferably, the phosphor particles have a non-light emitting shell layer on the surface of the particles. The shell layer is preferably formed with a thickness of 0.01 μm or more using a chemical method following the preparation of the semiconductor fine particles serving as the core of the phosphor particles. Preferably they are 0.01 micrometer or more and 1.0 micrometer or less.
The non-light-emitting shell layer can be formed from an oxide, nitride, oxynitride, or a material that is formed on the base phosphor particles and has the same composition and does not contain an emission center. Moreover, it can form with the substance of a different composition grown epitaxially on the base | substrate fluorescent substance particle material.
As a method of forming the non-light emitting shell layer, a laser ablation method, a CVD method, a plasma CVD method, a sputtering method, a resistance heating, an electron beam method, and a gas phase method such as a method combining fluid oil surface deposition, a metathesis method, Sol-gel method, ultrasonic chemistry method, precursor thermal decomposition method, reverse micelle method or a combination of these methods with high-temperature firing, hydrothermal synthesis method, urea melting method, freeze drying method, etc. A thermal decomposition method or the like can also be used.
In particular, the hydrothermal synthesis method, the urea melting method, and the spray pyrolysis method, which are preferably used in the formation of phosphor particles, are also suitable for the synthesis of a non-luminescent shell layer.

As an activator of the phosphor particles, at least one ion selected from copper, manganese, silver, gold and rare earth elements can be preferably used.
The phosphor particles of the present invention preferably contain at least one of Au, Mo, W, and Pt in an amount of 1 × 10 ⁻⁷ mol to 1 × 10 ⁻³ mol with ^{respect to} zinc. In particular, 3 × 10 ⁻⁶ mol or more and 3 × 10 ⁻⁴ mol or less is preferable.
As a more preferable state, it is preferable that Au is contained in the above-mentioned amount range, and that at least one metal ion selected from Mo, Bi, Sb, W, Pt and a group 8 metal is contained. The preferred addition amount of these second metal ions preferably contains at least one of Au, Mo, W, and Pt in an amount of 1 × 10 ⁻⁷ mol to 1 × 10 ⁻³ mol relative to zinc. In particular, 3 × 10 ⁻⁶ mol or more and 3 × 10 ⁻⁴ mol or less is preferable.
As the coactivator, at least one ion selected from chlorine, bromine, iodine and aluminum can be preferably used.

  In the electroluminescence device of the present invention, the thickness of the phosphor layer is preferably 30 μm or more and 60 μm or less. Particularly preferred is 40 μm or more and 55 μm or less.

The structure of the device has a light emitting layer containing a phosphor material sandwiched between a pair of opposed electrodes, at least one of which is transparent, and a phosphor light emitting layer containing a phosphor material and, if necessary, The total film thickness with the insulating layer containing the adjacent inorganic dielectric substance is preferably 2 to 10 times the average particle size of the phosphor, particularly preferably 3 to 5 times.
When the variation in the distance between the electrodes is viewed as the center line average roughness Ra in the element configuration, the element structure preferably has a smoothness of (d * 1/8) or less with respect to the light emitting layer thickness d.

The electroluminescent phosphor will be described in more detail below.
Specifically, the base material of the particles preferably used in the present invention includes one or more elements selected from the group consisting of Group II elements and Group VI elements, Group III elements and Group V elements. These are semiconductor fine particles composed of one or a plurality of elements selected from the group consisting of: and are arbitrarily selected depending on the necessary emission wavelength region. Examples thereof include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, CaS, MgS, SrS, GaP, GaAs, and mixed crystals thereof. Among them, ZnS, CdS, CaS, and the like can be preferably used.

Furthermore, as the base material of the _{particles, BaAl 2 S 4, CaGa 2} S 4, Ga 2 O 3, Zn 2 SiO 4, Zn 2 GaO 4, ZnGa 2 O 4, ZnGeO 3, ZnGeO 4, ZnAl 2 O 4, _{CaGa 2 O 4, CaGeO 3,} Ca 2 Ge 2 O 7, CaO, Ga 2 O 3, GeO 2, SrAl 2 O 4, SrGa 2 O 4, srP 2 O 7, MgGa 2 O 4, Mg 2 GeO 4, MgGeO ₃ , BaAl ₂ O ₄ , Ga ₂ Ge ₂ O ₇ , BeGa ₂ O ₄ , Y ₂ SiO ₅ , Y ₂ GeO ₅ , Y ₂ Ge ₂ O ₇ , Y ₄ GeO ₈ , Y ₂ O ₃ , Y ₂ O ₂ S, SnO ₂ and mixed crystals thereof can be preferably used.
In addition, as the emission center, metal ions such as Mn and Cr and rare earths can be preferably used.
By using several phosphors according to the selection of the base material, 0.3 <x <0.4, 0.3 on the chromaticity diagram without using any dye or fluorescent dye. White light emission in the range of <y <0.4 can also be obtained.

(Middle layer)
The electroluminescent element of the present invention preferably has at least one intermediate layer between the transparent conductive film and the luminescent particle-containing layer.
The intermediate layer may be an organic polymer compound or an inorganic compound, or a composite of these, but preferably has at least one layer containing an organic polymer compound.
The thickness of the intermediate layer is preferably from 10 nm to 100 μm, more preferably from 100 nm to 30 μm, and particularly preferably from 0.5 μm to 10 μm.
When the material forming the intermediate layer is an organic polymer compound, usable polymer compounds include polyethylene, polypropylene, polystyrene, polyesters, polycarbonates, polyamides, polyethersulfones, polyvinyl alcohol, pullulan and saccharose, Polysaccharides such as cellulose, vinyl chloride, fluororubber, polyacrylic acid esters, polymethacrylic acid esters, polyacrylic acid amides, polymethacrylic acid amides, silicone resin, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl saccharose, or Examples include an ultraviolet light curable resin obtained from a polyfunctional acrylic ester compound, and a thermosetting resin obtained from an epoxy compound or a cyanate compound. The polymer compound used here may be an insulator or a conductor.
These organic polymer compounds or their precursors are dissolved in a suitable organic solvent (for example, dichloromethane, chloroform, acetone, methyl ethyl ketone, cyclohexanone, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, toluene, xylene, etc.) on a transparent electrode. Or it can apply | coat and form to a light emitting particle content layer.

The intermediate layer may have additives for imparting various functions as long as it has substantial transparency (preferably the transmittance at a wavelength of 550 nm is 70% or more, more preferably 80% or more). . For example, a dielectric such as barium titanate particles, or a conductor such as tin oxide, indium oxide, tin-indium oxide, and metal particles, or dyes, fluorescent dyes, fluorescent pigments, or the extent that the effects of the present invention are not lost (electroluminescence Luminescent particles having 30% or less of the luminance of the entire device may be present.
The intermediate layer may be made of inorganic compounds such as silicon dioxide, other metal oxides, and metal nitrides. As a method for forming the intermediate layer with an inorganic compound, a sputtering method, a CVD method, or the like can be employed. When the intermediate layer is formed of an inorganic compound, the film thickness is preferably 10 nm or more and 1 μm or less, more preferably 10 nm or more and 200 nm or less.

It is also preferable that the intermediate layer is composed of a combination of an inorganic compound layer and an organic polymer compound layer.
In the present invention, it is preferable to have an intermediate layer containing at least one layer of an organic polymer compound and having a thickness of 0.5 μm to 10 μm. The organic polymer compound is a polyester, polycarbonate, polyamide, or polyethersulfone. , Fluoro rubber, polyacrylic acid esters, polymethacrylic acid esters, polyacrylic acid amides, polymethacrylic acid amides, silicone resins, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl saccharose, or polyfunctional acrylic acid ester compounds Those selected from the obtained ultraviolet light curable resins, thermosetting resins obtained from epoxy compounds and cyanate compounds are preferred, and among these, those having a softening point of 70 ° C. or higher (more preferably 100 ° C. or higher) are preferred. It is also preferred that a plurality of polymer compounds selected from these are combined.
When the organic polymer compound in the intermediate layer has a high softening point (for example, 200 ° C. or higher), the organic polymer compound has a low softening point for the purpose of improving the adhesion to the transparent electrode layer or the luminescent particle-containing layer. It is also preferable to use another intermediate layer containing

(White / fluorescent dye)
The use of the present invention is not particularly limited, but considering the use as a light source, the emission color is preferably white.
Examples of the method for making the emission color white include a method using phosphor particles that emit white light alone, such as a zinc sulfide phosphor that is activated by manganese with copper and gradually cooled after firing, or three primary colors or A method of mixing a plurality of phosphors that emit light in complementary colors is preferable. (Blue-green-red combination, blue-green-orange combination, etc.) Also, blue and blue-green colors described in JP-A-7-166161, JP-A-9-245511, and JP-A-2002-62530 It is also preferable to use a phosphor that emits light, a fluorescent pigment, or a fluorescent dye to convert a part of the light emission to green or red and to whiten it. As this preferable fluorescent dye, a rhodamine-based fluorescent dye is used. Further, the CIE chromaticity coordinates (x, y) preferably have an x value in the range of 0.30 to 0.4 and a y value in the range of 0.30 to 0.40.

(Back electrode)
For the back electrode on the side from which light is not extracted, any conductive material can be used. It is selected from gold, silver, platinum, copper, iron, aluminum and other metals, graphite, etc. according to the form of the element to be created, the temperature of the production process, etc., but among them, it is important that the thermal conductivity is high. Preferably, it is 2.0 W / cm · deg or more.
It is also preferable to use a metal sheet or a metal mesh in order to ensure high heat dissipation and electrical conductivity in the periphery of the EL element.

(Sealing / water absorption)
The EL element of the present invention is preferably processed so as to eliminate the influence of humidity from the external environment by finally using an appropriate sealing material. In the case where the element substrate itself has sufficient shielding properties, it is preferable that a shielding sheet is stacked on the created element and the periphery is sealed with a curable material such as epoxy. Further, a shielding sheet may be provided on both sides in order not to curl the planar element. When the substrate of the element has moisture permeability, it is necessary to provide a shielding sheet on both sides.
Such a shielding sheet is selected from glass, metal, plastic film and the like according to the purpose. For example, a layer made of silicon oxide and an organic layer as disclosed in Japanese Patent Application Laid-Open No. 2003-249349 are used. A moisture-proof film having a multilayer structure composed of a polymer compound can be preferably used, and ethylene trifluoride chloride and the like can also be preferably used.
As described in Japanese Patent Publication No. 63-27837, the sealing step is preferably performed in a vacuum or an atmosphere substituted with an inert gas. Prior to the sealing step, Japanese Patent Laid-Open No. 5-166582 discloses. As described, it is important to sufficiently reduce the moisture content.

When producing these EL elements, it is preferable to provide a water-absorbing layer inside the moisture-proof film. It is preferable that the water supply layer is made of a material having a high water absorption property such as nylon or polyvinyl alcohol and a high water retention capability. It is also important that transparency is high. As long as the transparency is high, materials such as cellulose and paper can be preferably used.
As described in JP-A-4-230996 and JP-A-11-260557, it is also preferable to improve moisture resistance by coating phosphor particles with metal oxide or nitride as well as moisture prevention by a film. Can be used together.

(Dielectric layer)
The dielectric material of the present invention may be a thin film crystal layer or a particle shape. A combination thereof may also be used. The dielectric layer containing the dielectric substance may be provided on one side of the phosphor particle layer, and is preferably provided on both sides of the phosphor particle layer. In the case of a thin film crystal layer, it may be a thin film formed on a substrate by a vapor phase method such as sputtering, or a sol-gel film using an alkoxide such as Ba or Sr. In the case of a particle shape, it is preferable that the size is sufficiently small with respect to the size of the phosphor particles. Specifically, a size of 1/3 to 1/1000 of the phosphor particle size is preferable.

(UV absorber)
In the present invention, inorganic compounds such as cerium oxide described in JP-A-9-22781 can be used. More preferably, an organic compound can be used.
In the present invention, a compound having a triazine bone core having a high molar extinction coefficient is preferably used as the ultraviolet absorber, and for example, compounds described in the following publications can be used.
These are preferably added to the photographic light-sensitive material, but are also effective in the present invention. For example, JP-A-46-3335, JP-A-55-15276, JP-A-5-197004, JP-A-5-232630, JP-A-5-307232, JP-A-6-218131, JP-A-8-53427, and 8- No. 234364, No. 8-239368, No. 9-31067, No. 10-115898, No. 10-147777, No. 10-182621, German Patent No. 19739797A, European Patent No. The compounds described in No. -502911, etc. can be used.
It is important that these ultraviolet absorbers are arranged so that the phosphor particles and the fluorescent dye do not absorb ultraviolet rays. The phosphor particles and the fluorescent dye are added to and dispersed in a binder in which the phosphor particles and the fluorescent dye are dispersed. It can be used by being added to a moisture-proof film or water-absorbing film outside the electrode layer. Of course, these films can also be used as an ultraviolet absorbing layer.

(binder)
As the phosphor layer, a phosphor layer in which phosphor particles are dispersed in a binder is used. As the binder, a polymer having a relatively high dielectric constant such as a cyanoethyl cellulose resin, or a resin such as polyethylene, polypropylene, polystyrene resin, silicone resin, epoxy resin, or vinylidene fluoride can be used. The dielectric constant can be adjusted by appropriately mixing fine particles having a high dielectric constant such as BaTiO ₃ or SrTiO _{3 with} these resins. As a dispersion method, a homogenizer, a planetary kneader, a roll kneader, an ultrasonic disperser, or the like can be used.

As the dielectric layer, any material can be used as long as it has a high dielectric constant and insulation and has a high dielectric breakdown voltage. These metal oxides are selected from nitrides, for example _{TiO 2, BaTiO 3, SrTiO 3} , PbTiO 3, KNbO 3, PbNbO 3, Ta 2 O 3, BaTa 2 O 6, LiTaO 3, Y 2 O 3, Al ₂ O ₃ , ZrO ₂ , AlON, ZnS, or the like is used. These may be installed as a uniform film, or may be used as a film having a particle structure.
The phosphor layer and the dielectric layer are preferably applied using a spin coating method, a dip coating method, a bar coating method, a spray coating method, or the like. In particular, it is preferable to use a method that does not select a printing surface, such as a screen printing method, or a method that allows continuous application, such as a slide coating method. For example, in the screen printing method, a dispersion liquid in which fine particles of phosphor or dielectric are dispersed in a polymer solution having a high dielectric constant is applied through a screen mesh. The film thickness can be controlled by selecting the thickness of the mesh, the aperture ratio, and the number of applications. By changing the dispersion liquid, not only the light emitting layer and the dielectric layer but also the back electrode layer can be formed, and further, the area can be easily increased by changing the size of the screen.

(Phosphor layer thickness)
In the EL device of the present invention, the phosphor layer is preferably thin, and particularly preferably 30 μm or more and 60 μm or less. Furthermore, the total film thickness of the dielectric layer and the phosphor layer is preferably 1.1 to 10 times the average particle size of the phosphor.
The lower limit of the phosphor layer thickness is the phosphor particle size, but the phosphor layer thickness is 1.0 to 10 times the phosphor particle size in order to ensure the smoothness of the element. It is preferable.

In the element structure of this invention, a board | substrate, a transparent electrode, a back electrode, various protective layers, a filter, a light-scattering reflection layer, etc. can be provided as needed. In particular, regarding the substrate, in addition to a glass substrate or a ceramic substrate, a flexible resin sheet can be used for the flexible substrate.
In the present invention, it is preferable to appropriately combine the phosphor particles having the above-described characteristics and the EL element configuration, thereby providing an EL element with high luminance and high efficiency.

(Power supply)
Usually, the dispersion type electroluminescence element is driven by alternating current. Typically, it is driven using an AC power source of 50V to 400Hz at 100V. When the area is small, the luminance increases almost in proportion to the applied voltage and frequency. However, in the case of a large-area element of 0.1 m ² or more, the capacitance component of the element increases, the impedance matching between the element and the power supply shifts, and the time constant required for the charge storage in the element increases, so the voltage increases In particular, even if the frequency is increased, the power supply tends to be insufficient. In particular, in an element of 0.25 m ² or more, for AC driving of 500 Hz or more, the applied voltage is often lowered with an increase of the driving frequency, and the luminance is often lowered. On the other hand, the electroluminescence element of the present invention can be driven at a high frequency even with a large size of 0.1 m ² or more, and can have high luminance. In that case, driving at 500 Hz to 5 KHz is preferable, and driving at 1 KHz to 3 KHz is more preferable.
In the present invention, it is preferable that the power source for driving the EL element has a function of detecting a current and keeping it constant.

Example 1
<Invention: phosphor particle A>
25 g of zinc sulfide (ZnS) particle powder having an average particle diameter of 30 nm, 0.1 mol% of copper sulfate with respect to ZnS, 0.003 mol% of chloroauric acid, and 0.005 of Na ₂ [Pt (OH) ₆ ] An appropriate amount of NaCl, MgCl ₂ and ammonium chloride (NH ₃ Cl) powder as fluxes, and magnesium oxide powder in a 20% by mass alumina crucible with respect to the phosphor powder are added to the dry powder added at mol% at 1200 ° C. The temperature was lowered after firing for 0 hours. Thereafter, the powder was taken out and pulverized and dispersed with a ball mill. After further ultrasonic dispersion, 5 g of ZnCl ₂ and 0.05 mol% of copper sulfate were added to ZnS, and then 1 g of MgCl ₂ was added to prepare a dry powder, which was again put in an alumina crucible at 700 ° C. for 6 hours. Baked. At this time, firing was performed while flowing 10% oxygen gas as an atmosphere.

After firing, the particles are pulverized again, dispersed and settled in 40 ° C. H ₂ O, removed and washed with a supernatant, then added with 10% hydrochloric acid to disperse, settled and removed the supernatant to remove unnecessary salts. Removed and dried. Further, a 10% KCN solution was heated to 70 ° C. to remove Cu ions and the like on the surface.
Further, the surface layer corresponding to 10% by weight of the whole particles was removed by etching with 6N hydrochloric acid.
The particles thus obtained were further sieved to take out monodispersed and small-sized particles.
The phosphor particles thus obtained had an average particle size of 16.0 μm and a coefficient of variation of 31%. In addition, the particles were pulverized in a mortar, and fragments having a thickness of 0.2 μm or less were taken out and observed under an electron microscope under an acceleration voltage condition of 200 KV. As a result, at least 80% or more of the fragments were laminated at intervals of 5 nm or less. A portion having 10 or more defects was included.

<Comparative Example: Phosphor Particle B>
In the production of the phosphor particles A, the amount of MgCl ₂ and the firing temperature / time were adjusted, and without sieving, phosphor particles B having an average particle diameter of 24 μm and a variation coefficient of 43% were produced.

<Comparative Example: Phosphor Particle C>
In preparation of phosphor particles A, phosphors were prepared without sieving. As a result, phosphor particles C having an average particle diameter of 18 μm and a particle size variation coefficient of 44% were obtained.

BaTiO ₃ fine particles having an average particle size of 0.02 μm were dispersed in a cyanoresin solution dissolved in an organic solvent at a ratio of 30% by mass, and applied on an aluminum sheet having a thickness of 75 μm so that the dielectric layer thickness was 25 μm. It dried for 1 hour at 120 degreeC using the warm air dryer.
The phosphor particle A is 30 wt% so that x = 3.3 ± 0.3 y = 3.4 ± 0.3 in the CIE chromaticity coordinate when emitting light of fluorescent dye FA-001 manufactured by Sinloihi Co., Ltd. and 300 cd / m 2. It was dispersed and kneaded in a cyanoresin solution having a concentration of%, and applied on the dielectric layer so as to have a thickness of 50 μm.

(Formation of intermediate layer)
On the phosphor layer, a coating solution in which BaTiO ₃ fine particles having an average particle size of 0.02 μm are dispersed in a cyanoresin solution in an amount 1/5 that of the dielectric layer is applied to a thickness of 2 μm. An intermediate layer was formed.

(Transparent conductive film)
Transparent conductive film A: A transparent film 0.5 m × 0.7 m substrate on which ITO was deposited was prepared. At this time, the surface resistance was 150Ω / □ and the light transmittance was 88%.
Transparent conductive film B: A transparent film 0.5 m × 0.7 m substrate on which ITO was deposited was prepared. At this time, the surface resistance was 30Ω / □ and the light transmittance was 77%.
Transparent conductive film C: On the other hand, a conductive film having a surface resistance of 350 Ω / □ with a surface resistance of 350 Ω / □ deposited with IZO (indium zinc oxide) and having a light transmittance of 93% is prepared, and Ni having a width of 10 μm and a height of 3 μm at a pitch of 300 μm is formed thereon. Striped metal fine wires made of the above were produced by vapor deposition using a mask. As a result, the surface resistance was 15Ω / □.
Transparent conductive film D: A conductive film having a surface resistance of 350Ω / □ on which IZO was vapor-deposited and having a light transmittance of 93% was prepared, and Au was vapor-deposited thereon by 10 nm. As a result, the surface resistance was 10Ω / □.

After taking out the terminal for external connection from the transparent electrode part of the element and the back electrode part of aluminum using a copper aluminum sheet having a thickness of 80 μm, and thermocompression bonding with a moisture-proof film having _two SiO ₂ layers. did.
The light-emitting elements of the present invention thus manufactured were designated as Sample 1 (Comparative Example), 2 (Invention), 3 (Invention) 4 (Invention). Based on this sample, samples 5 to 16 were prepared by changing the presence or absence of the intermediate layer and the phosphor particles. The drive was performed at 1 kHz with reference to Sample 1. The results are shown in Table 1.

Example 2
In Example 1, the fluorescent dye is replaced by F6013 manufactured by Sinloich, and a coating liquid mixed with the dielectric of Example 1 is created between the phosphor layer and the dielectric layer instead of the phosphor layer, and a high dielectric containing dye A fluorescent dye layer was applied as the body layer. The thickness was 18 μm. At this time, the coating thickness of the dielectric layer was reduced to 18 μm.
Evaluation of the color rendering index when 1 KHz 120 V was applied to the electroluminescence device thus prepared showed 80.
When the luminance of this sample was changed as shown in Table 2 by changing the voltage and frequency, the color temperature was measured, and it showed a color temperature of 5500 K at 400 cd / m ² or more, and a good white color was obtained. 80 or more were obtained.

Example 3
The element of the present invention of Example 1 (1) Processed to a size of 0.5 m × 0.8 m, (2) Relationship between driving frequency and efficiency of the sample of Example 1 processed to a size of 0.05 m × 0.10 m As a result of the investigation, it was found that the device of the present invention maintained excellent efficiency comparable to that of a small size despite its large size.

Example 4
When the device of the present invention was driven at a constant current at 1.3 KHz 140 V as an initial condition, it was confirmed that the half-life was extended more than twice as long as the device was driven at a constant voltage while maintaining high luminance and efficiency.

Claims (8)

  In a dispersive electroluminescent device having a phosphor layer containing phosphor particles between a pair of opposing electrodes, at least one of which is transparent, the surface resistivity of the transparent conductive film in the at least one transparent electrode is 0. 5. An electroluminescent device characterized by being 5Ω / □ to 80Ω / □, an average particle size of phosphor particles being 12 μm to 22 μm, and a coefficient of variation of particle size being 35% or less.   2. The electroluminescent device according to claim 1, further comprising an insulating intermediate layer made of an organic substance between the transparent conductive film of the transparent conductive film and the phosphor layer.   3. The electroluminescent device according to claim 1, wherein the phosphor layer has a thickness of 30 μm or more and 60 μm or less. 4. The electroluminescence element according to claim 1, wherein the electroluminescence element has a peak of emission intensity at 600 nm or more, emits white light, and is used at an initial luminance of 400 cd / m ² or more.   5. The electroluminescence device according to claim 1, wherein the phosphor particles contain at least one of Au, Mo, W, and Pt.   6. The electro according to claim 1, wherein the phosphor particles contain Au, and further contain at least one metal ion selected from Mo, Bi, Sb, W, Pt and a group 8 metal. Luminescence element. 7. The electroluminescence element according to claim 1, wherein a light emitting area is 0.1 m ² or more.   8. A light emitting element system using the electroluminescence element according to claim 1, wherein a power source for driving the electroluminescence element has a function of detecting a current and keeping it constant. A light emitting device system characterized by the above.