Title of Invention

INORGANIC PHOSPHOR MATERIAL AND DISPERSION-TYPE ELECTROLUMINESCENCE DEVICE

Technical Field

The present invention relates to a dispersion-type electroluminescence device and an inorganic phosphor material useful for the manufacture of the dispersion-type electroluminescence device.

Background Art

Phosphors are materials that emit light by energy given from the outside such as light, electricity, pressure, heat, electron beam, etc., and phosphors comprising organic materials have been used in Braun tubes, fluorescent lamps, electroluminescence (EL) devices, and the like for their light emitting characteristics and stability. In recent years, studies of phosphors as color conversion materials for LED and low speed electron beam-exciting phosphors in PDP are also eagerly tried.

A phenomenon that emits light by the application of an electric field to a phosphor is called electroluminescence (EL), and light-emitting devices making use of this phenomenon are called electroluminescence (EL) devices. The EL devices include two kinds of a dispersion-type EL device of forming a light-emitting layer by dispersing phosphor particles in a binder having a high dielectric constant, and a thin film-type EL device of sandwiching a phosphor thin film between dielectric layers. Of these two types, since the dispersion-type EL device does not use high temperature process in the manufacture, the device is characterized in that it is possible to form a flexible device using a plastic as a substrate, and also the manufacture is possible by a relatively simple and inexpensive process without using a vacuum apparatus. Further, it is possible for the dispersion-type EL devices manufactured with phosphor particles to have a thickness of several millimeters or less, and they have many advantages such that they are light sources emitting from the surface, little in heat generation, and good in light emitting efficiency, so that various uses are expected of the dispersion-type EL devices such as road signs, various indoor and outdoor illuminations, light sources for flat panel displays such as liquid crystal display, and light sources of illuminations for advertisement of large area.

When dispersion-type EL devices are used as the light sources of backlights and illuminations, luminescent color is preferably white, but phosphors that emit white light alone are not known. Accordingly, it is necessary to combine some luminescent colors. For example, white light emission can be obtained by combinations of blue green emission-red emission, and blue emission-yellow emission. However, in phosphors for dispersion-type inorganic EL devices, there are no promising phosphors even now other than ZnSrCu, Cl showing blue green emission, and phosphors showing red emission (emission peak wavelength: 600 nm or higher) are hardly known.

Accordingly, in prior techniques, it has been examined to obtain white emission by adding ZnS: Cu, Cl phosphors that emit blue-green light by electroluminescence and organic compounds that emit red light by absorbing the luminescent color of the ZnS: Cu, Cl phosphors to a light-emitting layer and combining both light emissions (JP-A-2-78188 and JP-A-2006-156358, the term "JP- A" as used herein refers to an "unexamined published Japanese patent application"). However, these inorganic EL devices are in a colored state even at non-luminescent time due to the added organic compounds. Therefore, although white emission can be obtained by the application of electric field, this technique is unsuitable for ordinary illumination uses for the sake of appearance at non-luminescent time.

On the other hand, in the thin film-type inorganic EL, as phosphor materials emitting in red, materials such as ZnGa ₂ S ₄ :Mn, Ba ₂ ZnS ₃ :Mn are known from old (JP- A-55-147584, JP-A-2005-162948, and Journal of Vacuum Science & Technology, Vol. 10, p. 789 (1973)).

Summary of Invention

However, by the application of these materials to dispersion-type inorganic EL by the present inventors, red emission by electric field application could not be obtained. This is considered due to the difference in mechanism of the thin film-type and dispersion-type.

In the thin film-type inorganic EL, an electron emitted from the interfacial level of a light-emitting layer and an insulating layer at the time of application of electric field and further accelerated by the electric field (a hot electron) excites the emission center to emit light. On the other hand, in the dispersion-type inorganic EL, electron-generating sources are present in the stacking fault in the phosphor particles (for example, needle crystal of Cu ₂ S), and electrons and holes are discharged from the sources by the application of the electric field, and light is emitted by recombination of them after they are captured by donor and acceptor levels; or the recombined energy becomes an exciting energy of other emission center present in the particles to emit light. Accordingly, it is thought that even if phosphors for thin film-type EL not having electron-generating sources are diverted to dispersion-type inorganic EL as they are, electrons exciting emission center do not generate, so that emission could not be obtained.

Therefore, an object of the invention is to obtain a dispersion- type electroluminescence device emitting light in red, and another object is to obtain an inorganic phosphor material useful for manufacture of the dispersion-type electroluminescence device.

As a result of earnest examinations, the present inventors have found a novel inorganic phosphor material showing red emission in photoluminescence by ultraviolet excitation and electroluminescence in the case of alternating current dispersion-type device by the addition of at least one element selected from the elements belonging to group XIII, Cu, and Mn to a compound containing at least one element belonging to group XII and at least one element belonging to group XVI of the Periodic Table. Thus the invention has been accomplished.

That is to say, the invention has been accomplished by the following requisites.

(1) An inorganic phosphor material, including: a base material which is a mixed crystal including at least one or two or more compounds, the compounds being selected from compounds containing at least one element belonging to group XII and at least one element belonging to group XVI of the Periodic Table, wherein the base material contains at least one element selected from elements belonging to group XIII of the Periodic Table, Cu, and Mn.

(2) The inorganic phosphor material as described in (1), wherein the element selected from elements belonging to group XIII is Al, Ga or In.

(3) The inorganic phosphor material as described in (1) or (2), the inorganic phosphor material being phosphor particles, wherein 20% or more of the phosphor particles in particle number are particles each of which has 10 or more planar stacking faults at intervals of 5 nm or less with respect to the total number of the phosphor particles.

(4) The inorganic phosphor material as described in (3), wherein the phosphor particles have an average particle size of 20 μm or less and a variation coefficient in particle sizes of 40% or less.

(5) A dispersion-type electroluminescence device, including: a light-emitting layer; and the inorganic phosphor material as described in any of (1) to (4) in the light- emitting layer.

Brief Description of Drawings

Fig. 1 is a drawing showing the outline of the structure of the dispersion-type inorganic EL device manufactured in examples and comparative examples, wherein 1 and 8 denote sealing films, 2 denotes a film base (PET), 3 denotes a indium-tin-oxide (transparent electrode), 4 denotes an inorganic phosphor material, 5 denotes a phosphor layer, 6 denotes a dielectric layer, and 7 denotes an aluminum electrode.

Description of Embodiments

The invention will be described in detail below. Inorganic phosphor material:

The inorganic phosphor material according to the invention is an inorganic phosphor material with a mixed crystal as a base material including at least one or two or more compounds selected from the compounds containing at least one element belonging to group XII and at least one element belonging to group XVI of the Periodic Table, and at least one element selected from the elements belonging to group XIII, and Cu and Mn are contained in the base material.

Incidentally, the compounds containing at least one selected from group XII elements and at least one selected from group XVI elements of the Periodic Table that are used as the base materials of the inorganic phosphor materials of the invention are described as "XII group-XVI group compounds" in some cases, which terminology is the description generally used by those having ordinary knowledge in the technical field to which the invention belongs.

The examples of the elements belonging to group XII of the Periodic Table for use in the base material of the inorganic phosphor material of the invention include Zn, Cd and Hg, and it is preferred to use Zn or Cd.

The examples of the elements belonging to group XVI of the Periodic Table include O, S, Se, Te and Po, and it is preferred to use S, Se or Te.

As the examples of the base materials, ZnS, ZnSe, ZnSSe, ZnTe, CdS, CdSe, CdTe and the like are used. ZnS, ZnSe and ZnSSe are preferably used, and ZnS is more preferably used.

The inorganic phosphor material of the invention contains at least one of the elements belonging to group XIII of the Periodic Table and Cu and Mn, by which an inorganic phosphor material showing emission in a red region can be obtained when the material is used in a dispersion-type electroluminescence device. For example, a phosphor containing Mn in ZnS generally has an emission peak wavelength in the vicinity of 580 nm of an orange region. Contrary to this, the emission peak wavelength of the inorganic phosphor material of the invention shows emission of a red region longer than the orange region, so that it is preferred as a phosphor for the dispersion-type inorganic EL of red emission. Light emission of Mn is by transition in ion called d-d transition by the (3d ⁵ ) electron present on 3d orbit Of Mn ²⁺ , and 3d orbit is the outermost shell OfMn ²⁺ ion, so that it is strongly influenced by the crystal field. It is presumed that the ionic bonding property of a crystal rises by the addition of the elements belonging to group XIII such as Al, Ga, etc., to ZnS, and the strength of the crystal field around Mn ²⁺ increases, as a result energy level in an excitation state lowers and emission wavelength becomes longer.

In the thin film-type inorganic EL, ZnGa ₂ S ₄ :Mn is examined as a red emission phosphor material on the basis of the above concept. However, in the case of the dispersion-type inorganic EL, since electron-generating sources are further necessary in the particles, light emission cannot be obtained even if the ZnGa ₂ S ₄ IMn is used as it is. In a phosphor for the dispersion-type inorganic EL, for example, in the case of the base material being ZnS, the crystal structure includes two kinds of a hexagonal system and a cubic system, and stacking faults are taken in the crystal when the crystal system is converted by the application of heat and stress, and Cu ₂ S to become an electron-generating source can be stably present at the part of the stacking faults. On the other hand, since the crystal structure OfZnGa ₂ S ₄ is a tetragonal system alone, stacking faults cannot be formed like ZnS, and cannot be present as an electron- generating source in the particles even by doping with Cu. Accordingly, light emission cannot be obtained with a dispersion-type inorganic EL.

According to the invention, by containing at least one element selected from the elements belonging to group XIII of the Periodic Table, and Cu and Mn in the base material of phosphor particles, an inorganic phosphor material showing light emission in a red region of the emission peak wavelength of 600 nm or more in the case of being used in a dispersion-type EL device can be obtained.

Further, by forming stacking faults in the base material, light emission in a red region of the emission peak wavelength of 600 nm or more can be preferably obtained in dispersion-type inorganic EL.

The method of addition of the element belonging to group XIII of the Periodic Table, that is to say, a method of doping, to a base material is not restricted and any method may be used. For example, the element may be mixed with the base material in the form of a metal salt at the time of forming phosphor particles by baking, or may be mixed in the form of a compound crystal, if fusion, sublimation or reaction is possible in the condition of baking. Further, the element may be introduced by the method of making an aqueous solution of the metal salt, adding the aqueous solution to a suspension of the base material with stirring, and baking it after evaporating the solvent. As such compounds, any compound may be used, e.g., an oxide, a sulfide, an oxysulfide, an oxalate, a halide, a nitrate, and a nitride are exemplified, and of these compounds, a sulfide, an oxide and a halide are especially preferably used. The amount of doping is preferably from IxIO ^"3 to 5XlO ^"1 mol per mol of the base material, and more preferably from 5xlO ^"3 to IxIO ^"1 mol.

The preferred examples of the elements belonging to group XIII of the Periodic Table for use in the inorganic phosphor material of the invention include B, Al, Ga, In and Tl, and it is preferred to use Al, Ga and In.

When the phosphor particles of the invention are doped with Cu and Mn, methods similar to the methods of doping of the base material of the invention with the element belonging to group XIII of the Periodic Table can also be used. As the doping amount of Cu is preferably from IxIO ^'4 to Ix 10 ^"2 mol per mol of the base material, and more preferably from 5xlO ^"4 to 5xlO ^"3 mol. The doping amount of Mn is preferably from IxI(T ³ to Ix 10 ^"1 mol per mol of the base material, and more preferably from 5xlO ^"3 to 5xlO ^"2 mol.

The phosphor material of the invention is phosphor particle, and particles of 20% or more in particle number of all the particles are preferably particles containing 10 or more planar stacking faults at intervals of 5 nm or less, and more preferably particles containing 10 or more planar stacking faults at intervals of 5 nm or less account for 30% or more.

"Stacking faults" used here indicates twin planes and phase interface. Taking ZnS as an example, these planes generally become planer faults perpendicular to a {111} face. Ordinary description as to stacking faults is described in detail in B. Henderson, Lattice Defect, Chapters 1 and 7, translated by Masao Dohyama, published by Maruzen Co., Ltd. In the case of ZnS, stacking faults are described in Andrew C. Weight and Ian V.F. Viney, Philosophical Mag. B, 2001, Vol. 81, No. 3, pp. 279-297.

Stacking faults are evaluated by observation of the structure of lamination appearing on particle side face (the surface of particle) in etching a phosphor particle with an acid, e.g., a hydrochloric acid. Stacking faults are present at the interface of layer structures and come to appear like stripes on the surface by etching. Such layer structures are present in the entirety of one particle, and can be clearly numbered with SEM and TEM. When the material is pulverized and cleaved perpendicularly to the stacking fault plane, layer structures can also be clearly observed with TEM. For example, by grinding phosphor particles with an agate mortar and observing the broken pieces of particles with TEM, it is also possible to directly observe the intervals and numbers of the stacking faults. Particles containing at least 10 or more planar stacking faults at intervals of 5 nm or less are stacking fault particles in the invention.

In connection with the plane intervals of stacking faults, minute structures are known to be present. When a TEM image of the broken piece of a particle of the pulverized inorganic phosphor material of the invention is observed, there are cases where the particle containing 10 or more planar stacking faults at intervals of 5 nm or less is observed. It is preferred for the inorganic phosphor material of the invention to have the particles containing 10 or more planar stacking faults at intervals of the density as high as 5 nm or less like this, more preferably to have 15 or more, and still more preferably 18 or more.

The average particle size of the particles constituting the phosphor particles is preferably 20 μm or less, more preferably 18 μm or less, and preferably 50 nm or more. This is for the reason that the density of the stacking faults is preferably high. The variation coefficient of the particle sizes of the invention can be computed by the equation of (standard deviation of particle size distribution of volume summation ÷ average particle size of volume summation x 100 (%)), and the variation coefficient is preferably 40% or less, more preferably 38% or less, and preferably 15% or more. The variation coefficient in this range is preferred from the manufacturing point. The volume of each particle is calculated in terms of sphere and the particle size is expressed as the sphere-equivalent diameter. The particle size may be measured from the photograph of the particle, or the distribution may be optically measured, or the distribution may be computed from precipitation velocity.

Here, the average particle size is a median size.

Stacking faults in the phosphor particles of the inorganic phosphor material of the invention are spontaneously generated by baking, but it is preferred to perform baking two times and the conditions of the first baking and the second baking are properly selected so that more stacking faults are contained in the fine phosphor particles.

Additionally, the density of stacking faults in phosphor particles can be substantially increased without destroying the particles by imposing an impact force of magnitude within a certain range on the particles, preferably the baked particles obtained by the first baking (intermediate phosphor particles).

Examples of a method which can be used suitably for application of an impact force to phosphor particles include a method of bringing the particles into contact mixing, a method of mixing the particles in the presence of spherical bodies like alumina (by means of a ball mill), a method of accelerating the particles and making them collide with one another, a method of irradiating the particles with ultrasonic waves, a method of applying hydrostatic pressure to the particles, and a method of generating momentary pressure by the burst shock of an explosive or the like.

As a method for making an impact on phosphor particles, the method of using a ball mill is preferable. Hereinafter, the method of using a ball mill will be described as an example.

The material which can be suitably used for the vessel and balls of a ball mill is glass, alumina, zirconia or the like, but in point of contamination with balls, alumina and zirconia are preferable to others. It is appropriate that the diameters of balls used be within the range of 0.01 to 10 mm, preferably 0.05 to 1 mm. By choosing the optimum diameters of balls, the balls can be easily separated from the intermediate phosphor particles after the treatment, what's more, the intermediate phosphor particles are easy to avoid crushing and undergo uniform stress. Mixing with two or more kinds of balls different in diameter is also favorable, because the mixing makes it possible to apply uniform stress to the intermediate phosphor particles.

The suitable proportions in which the intermediate phosphor and balls are mixed are within the range of 1-100 parts by mass balls, preferably 2-20 parts by mass balls, to 1 part by mass intermediary phosphor. The suitable loading rate of a ball-intermediary phosphor mixture is within the range of 10-60 vol% to the volume of the vessel. The number of revolutions of a ball mill is chosen as appropriate in accordance with the outside diameter of the vessel. The suitable linear velocity during the revolutions is within the range of 1-500 cm/sec, preferably 10-100 cm/sec, and it is appropriate that the number of revolutions be adjusted to impart a semicircular motion to the ball-intermediate phosphor mixture in the vessel and bring the tilt angle of balls in revolution into a range of 5-45 degrees. The suitable operation time of a ball mill, though varies depending on the conditions including the number of revolutions, is within the range of 1 minute to 24 hours, preferably 10 minutes to 3 hours. It is preferred that those conditions be combined as appropriate from the luminance and longevity of the EL phosphor.

The foregoing is a method of operating the ball mill under dry conditions. In the case of operating the ball mill under wet conditions, on the other hand, organic solvents such as alcohols and ketones can be used in addition to water. Although the optimum amount of solvents added is an amount just enough to fill in gaps between balls, addition of solvents in an amount 1 to 10 times as large as the loading volume is adequate for enhancing flowability of the mixture. By optimizing the amount of solvents added, the flowability of the mixture is kept and application of uniform stress becomes easy. For the purpose of enhancing flowability of the mixture, a surfactant, water glass or the like may be added as a dispersant. And it is preferred that other conditions adopted for operating the wet ball mill be within the same ranges as those for operating the dry ball mill.

In the case of applying stress by means of balls, it is also possible to use a device for forcedly stirring the balls with an impeller, a rotor or the like, a device for vibrating the vessel, or so on.

The probability of generation of stacking faults by simple application of an impact force is low, and stacking faults are generated at high densities by further performing subsequent burning.

The method applicable to formation of the present inorganic phosphor material may be identical with the baking method (solid-phase method) widely used in the field except that it includes the process of introducing a greater number of stacking faults.

Taking the case of zinc sulfide, fine-particle powder having particle diameters in the 10- to 50-nm range (referred to as crude powder) is prepared by the liquid- phase method and used as primary particles. Impurities called activators are mixed in the primary particles, and the resulting particles are placed in a crucible together with flux and subjected to first baking at a high temperature of 900 ⁰ C and 1,300 ⁰ C for a time period of 30 minutes to 10 hours, thereby obtaining particles. The particles as intermediate phosphor powder obtained by the first baking are washed repeatedly with ion exchange water to remove alkali metals or alkaline-earth metals and excesses of activator and co-activator. In this course, it is preferred that the process of introducing stacking faults be employed as appropriate. And subsequently the intermediate phosphor powder thus obtained is subjected to second baking. The second baking is performed by heating (annealing) at a lower temperature of 500 ⁰ C to 800 ⁰ C for a shorter time period of 30 minutes to 3 hours as compared to the first baking. EL Device:

The dispersion-type electroluminescence device (hereinafter referred to as the EL device of the invention in some cases) using the inorganic phosphor material of the invention is described below.

The dispersion-type EL device using the inorganic phosphor material of the invention has, for example, at least one light-emitting layer containing the inorganic phosphor material of the invention between a pair of opposed electrodes, one of which is a transparent electrode. It is preferred to arrange dielectric layers such as an insulating layer and a cut-off layer between the light-emitting layer and the electrode for the purpose of preventing dielectric breakdown of the EL device and concentrating a stable electric field to the light-emitting layer.

In the next place, the dispersion-type inorganic EL device using the inorganic phosphor material of the invention is described below.

The dispersion-type electroluminescence device of the invention (preferably an AC dispersion-type EL device) comprises at least a dielectric layer, a phosphor layer, and a pair of electrodes having these layers between them, and one of the electrodes is generally a transparent electrode. Transparent Electrode:

The surface resistivity of transparent electrode used suitably in the invention is preferably 10 Ω/D or below, far preferably from 0.01 to 10 Ω/D, particularly preferably from 0.01 to 1 Ω/D.

The surface resistivity of transparent electrode can be measured in conformance with the method described in JIS K6911.

The transparent electrode is formed on a glass or plastic substrate, and it preferably contains tin oxide.

As the glass, though typical glass such as non-alkali glass or soda-lime glass can be used, glass having high heat resistance and high flatness is preferably used. As the plastic substrate, transparent film such as polyethylene terephthalate film, polyethylene naphthalate film or cellulose triacetate base can be used to advantage. On any of these substrates, a transparent conductive substance such as indium tin oxide (ITO), tin oxide or zinc oxide can be deposited and formed into film by evaporation, coating, printing or a like method.

In this case, it is favorable for enhancement of durability that tin oxide predominates in the surface layer of the transparent electrode.

The deposition amount of a transparent conductive substance as a constituent of the transparent electrode is preferably from 100% to 1% by mass, far preferably from 70% to 5% by mass, further preferably from 40% to 10% by mass, of the transparent electrode.

The method for preparing a transparent electrode may be a gas phase method such as sputtering or vacuum evaporation. Alternatively, ITO or tin oxide in a pasty state may be formed into film by coating or screen printing and heated in its entirety, or it may be formed into film by heating with laser.

For the transparent electrode used in the present EL devices, any of commonly used transparent electrode materials may be used. Examples of such a transparent electrode material include oxides, such as tin-doped tin oxide, antimony-doped tin oxide, zinc-doped tin oxide, fluorine-doped tin oxide and zinc oxide, a multilayer structure having a thin silver layer sandwiched between high-refraction layers, and conjugated polymers such as polyaniline and polypyrrole.

For further lowering the resistance, it is appropriate that current-carrying properties be improved by disposing reticulated or banded metallic fine wires, such as grid-shaped or comb-shaped metallic fine wires. Suitable examples of metal or alloy for the fine wires include copper, silver, aluminum and nickel. Such metallic fine wires may have an arbitrary thickness, but the preferred range of their thickness is from around 0.5 μm to 20 μm. The metallic fine wires are preferably disposed with 50-μm to 400-μm pitches, especially with 100-μm to 300-μm pitches. Since the light transmittance is reduced by disposing metallic fine wires, minimization of this reduction is important, and it is advantageous to ensure the light transmittance in a range of 80% to less than 100%.

The meshes of metallic fine wire may be stuck on transparent conductive film, or metal oxide or the like may be coated or deposited on metallic fine wires formed in advance on the film by mask evaporation or etching. Alternatively, the metallic fine wires may be formed on a thin film of metal oxide prepared in advance.

On the other hand, though different from the above in forming method, transparent electrode suitable for the invention can be formed by lamination of metal oxide and a metallic thin film having an average thickness of 100 nm or below instead of metallic fine wires. As metals used for the metallic thin film, those having high corrosion resistance and excellent malleability and ductility, such as Au, In, Sn, Cu and Ni, are suitable, but usable metals are not limited to those metals in particular.

It is preferred that such multilayer film achieve high light transmittance, specifically light transmittance of 70% or higher, particularly preferably 80% or higher. The wavelength at which the light transmittance is defined is 550 nm.

The light transmittance can be measured by using an interference filter for extraction of 550-nm monochromatic light and integration actinography using a typical white light source, or with a spectrum measuring device. Back Electrode:

Any of electrically conductive materials can be used for the back electrode provided on the side of which no light is taken out. According to the form of a device to be made, the temperatures in making processes and so on, the electrically conductive material for the back electrode can be chosen as appropriate from among metals, such as gold, silver, platinum, copper, iron and aluminum, or graphite. And it is important for the material chosen to have high thermal conductivity, preferably a thermal conductivity of 2.0 W/cmdeg or higher.

For ensuring a high degree of heat dissipation into the periphery of the EL device and high current-carrying capacity, the use of a metal sheet or a mesh of metal wires is also suitable. Light-emitting layer (phosphor layer):

In the dispersion- type electroluminescence device of the invention, it is preferred for the light-emitting layer to contain the inorganic phosphor material.

When an AC dispersion-type EL device is manufactured with the inorganic phosphor material of the invention, the phosphor layer is formed by dispersing the particles in an organic dispersion medium and coating the obtained dispersion. As the organic dispersion medium, organic polymeric materials or organic solvents having a high boiling temperature can be used, but organic binders mainly comprising organic polymeric materials are preferred.

As the organic binders, materials having a high dielectric constant are preferably used. The examples of such materials include fluorine-containing polymeric compounds (e.g., polymeric compounds containing ethylene fluoride or ethylene monochloride trifluoride as a polymerization unit), polysaccharides having a cyano-ethylated hydroxyl group (e.g., cyanoethyl pluran, cyanoethyl cellulose), polyvinyl alcohols (cyanoethyl polyvinyl alcohol), and resins, e.g., phenol resins, polyethylene, polypropylene, polystyrene-based resins, silicone resins, epoxy resins, and vinylidene fluoride, and it is preferred for the light-emitting layer to contain all or a part of them as the organic binder. It is also possible to adjust the dielectric constant by properly mixing fine particles having a high dielectric constant, e.g., BaTiO ₃ and SrTiO ₃ , to these binders.

It is preferred to determine the blending proportion of the binder and the light- emitting particles so that the content of the light-emitting particles in the phosphor layer is 30 to 90% by mass to all the solids content, and more preferably 60 to 85% by mass. As the binder, it is preferred to use the polymeric compound having a cyanoethylated hydroxyl group in an amount of 20% or more in mass ratio of the organic dispersion medium in the light-emitting particle-containing layer as a whole, and more preferably 50% or more.

The thickness of the thus-obtained phosphor layer is preferably 1 μm or more and 200 μm or less, and more preferably 3 μm or more and 100 μm or less.

As disclosed in JP-A-2004-137482, it is also preferred to use the inorganic phosphor materials of the invention to be covered with a non-light-emitting shell comprising an oxide, a sulfide, or a nitride. Dielectric layer:

The AC dispersion-type inorganic EL device of the invention preferably has a dielectric layer on the opposite side of the transparent electrode from the phosphor layer. The dielectric layer may be formed with arbitrary materials so long as they have high dielectric constant and insulating property, and high dielectric breakdown voltage. The materials are selected from metal oxides and 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, etc., are used. These may be provided as a thin film crystal layer, or may be used as a film having a particle structure, or may be combinations thereof. Manufacturing method:

In the AC dispersion-type EL device of the invention, a phosphor layer and a dielectric layer are preferably formed by dissolving the forming materials in a solvent and coating the resulting coating solution with a spin coating method, a dip coating method, a bar coating method, or a spray coating method. It is especially preferred to use a method of not selecting the face to be printed such as a screen printing method, and a method of capable of continuous coating such as a slide coating method. In coating of these methods, it is preferred to prepare coating solutions to be used by adding proper organic solvents to the constituting materials of the phosphor layer and dielectric layer. As the organic solvents preferably used, dichloromethane, chloroform, acetone, acetonitrile, methyl ethyl ketone, cyclohexanone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, toluene, and xylene are exemplified. It is especially preferred to form the phosphor layer by continuous coating in a dry coating thickness of the coated film of 5 μm or more and 50 μm or less.

Each layer to be coated on a support is preferably formed by a continuous process of at least from coating to drying. The drying process is divided into a constant rate drying process of until the coated film is dried and solidified and a decreasing rate drying process of decreasing the residual solvent in the coated film. In the drying process, the constant rate drying process is preferably performed moderately with sufficient temperature for the solvent to be dried and then the decreasing rate drying process is performed. As a method for performing the constant rate drying process moderately, it is preferred that the drying chamber through which the support is traveling is divided to several zones and drying temperature after termination of the coating process is stepwise raised. Sealing:

It is preferred that the dispersion-type EL device of the invention is finally processed to exclude the influence of humidity and oxygen from the outside environment with a sealing film. The details of sealing are disclosed in JP-A-2007- 12466, paragraphs [0050] to [0055].

Examples

The invention will be described with reference to examples. However, the invention is by no means restricted thereto. EXAMPLE 1

Dried powder comprising 25 g of zinc sulfide (ZnS) particles, gallium sulfide in an amount of 5x10 ^"2 mol/mol in terms of Ga, copper sulfide in an amount of 9x10 ^{" 4} mol/mol in terms of Cu, and manganese sulfide in an amount of 3x10 ^"2 mol/mol in terms of Mn, each based on the zinc, appropriate amounts of NaCl, MgCl ₂ and ammonium chloride (NH ₃ Cl) as fluxes, and magnesium oxide powder in an amount of 10% by mass of the phosphor powder are put in an alumina crucible, baked at l,150°C for 2 hours (first baking), and then the temperature is lowered. A glass bottle of 15 mmφ is filled with 5 g of the particles after baking and 20 g of alumina balls of 1 mmφ, and they are subjected to ball milling for 20 minutes at a rotation speed of 10 rpm. After that, the alumina balls and intermediate phosphor particles are separated with a 100 mesh sieve. Further, 5 g of ZnO and 0.25 g of sulfur are added thereto to prepare dried powder, and the dried powder is put in the alumina crucible again and baked at 700°C for 6 hours (second baking). The particles after baking are pulverized again, dispersed in H ₂ O at 4O ⁰ C, and precipitated. After removing the supernatant, the particles are washed. After that, 10% by mass of a hydrochloric acid aqueous solution is added thereto to perform dispersion, precipitation, removal of the supernatant, removal of unnecessary salts, and drying. Further, 10% by mass of a KCN aqueous solution is heated at 70 ⁰ C to eliminate the oxide, e.g., ZnO, from the surfaces of the particles. Subsequently, the surface layers accounting for 10% by mass of the particles as a whole are excluded by etching with 0.1N hydrochloric acid.

From the thus-obtained particles, small size particles are separated by sieving.

On observation of the thus-obtained phosphor particles with an electron microscope and examination of the particle sizes of 500 particles, the average particle size is 19 μm and the variation coefficient of the particle sizes is 38%. Further, the phosphor particles are ground in a mortar and broken pieces of particles having a thickness of 0.2 μm or less are taken out. On observation of the pieces with an electron microscope on the condition of accelerating voltage of 200 kV, it has been found that 25% (number of the particles) of the observed broken pieces of particles contain the parts having 10 or more planar stacking faults at intervals of 5 ran or less (shown in Table 1 below as high density stacking fault containing frequency (particle number %)).

An AC dispersion-type inorganic EL device is manufactured with the above- prepared inorganic phosphor material. The outline of the structure of the AC dispersion-type inorganic EL device is shown in Fig. 1.

On the aluminum electrode (back electrode) (7) having a thickness of 70 μm, each of the following shown first layer, second layer are coated in this order with each layer-forming coating solution. Further, polyethylene terephthalate (thickness: 75 μm) (2) sputtered with indium tin oxide (3) to form a transparent electrode having a thickness of 40 nm is pressure-bonded to the aluminum electrode (7) by means of a heat roller at 190°C in the nitrogen atmosphere so that the transparent electrode (3) side (conductive face side) faces the aluminum electrode (7) side and the transparent electrode (3) and the phosphor layer (5) of the second layer are contiguous to each other.

The addition amount in each layer shown below is the mass per a square meter of the EL device. First layer: Dielectric layer (6) (layer thickness: 30 nm)

Cyanoethyl pluran 14.0 g

Cyanoethyl polyvinyl alcohol 10.0 g

Barium titanate particles (average equivalent-sphere diameter: 0.05 μm)

100.0 g Second layer: Phosphor layer (5) (layer thickness: 55 nm)

Cyanoethyl pluran 18.0 g

Cyanoethyl polyvinyl alcohol 12.0 g

The above-prepared inorganic phosphor material (4)

120.0 g

The viscosity of the coating solution for forming each layer is adjusted by adding dimethylformamide and the layer after coating is dried at 110°C for 10 hours.

As described above, the film (2) having the transparent electrode (3) is pressure-bonded with the thus-obtained coated substance, and the aluminum electrode (7) and the transparent electrode (3) are respectively wired for an electrode terminal (an aluminum plate having a thickness of 60 μm) and both electrodes are sealed with a sealing film (ethylene trifluoride polychloride, thickness: 200 μm) (1, 8) to manufacture an AC dispersion-type inorganic EL device. EXAMPLE 2

An inorganic phosphor material is manufactured in the same manner as in Example 1 except for replacing gallium sulfide with aluminum sulfide. EXAMPLE 3

An inorganic phosphor material is manufactured in the same manner as in Example 1 except for replacing gallium sulfide with indium sulfide. EXAMPLE 4

An inorganic phosphor material is manufactured in the same manner as in Example 1 except for replacing gallium sulfide with boron sulfide. EXAMPLE 5

An inorganic phosphor material is manufactured in the same manner as in Example 1 except for replacing gallium sulfide with thallium sulfide. EXAMPLE 6

An inorganic phosphor material is manufactured in the same manner as above except for changing the ball milling time to 60 minutes. On observation of the material with an electron microscope in a similar manner, it has been found that 32% of the particles contain the parts having 10 or more planar stacking faults at intervals of 5 nm or less. EXAMPLE 7

An inorganic phosphor material is manufactured in the same manner as above except for changing the time of the first baking to 6 hours. On observation with an electron microscope, the average particle size is 29 μm and the variation coefficient of the particle sizes is 43%. COMPARATIVE EXAMPLE 1

An inorganic phosphor material is manufactured in the same manner as above except for not adding gallium sulfide. COMPARATIVE EXAMPLE 2

An inorganic phosphor material is manufactured in the same manner as above except for not adding copper sulfide. COMPARATIVE EXAMPLE 3

An inorganic phosphor material is manufactured in the same manner as above except for not adding manganese sulfide.

The results of emission wavelength and emission strength obtained by applying AC electric field of 1 kHz, 100 V to each device manufactured with the obtained phosphor are shown in Table 1. EL emission strength shows a relative strength taking the emission strength in Example 1 as 100.

TABLE 1

Ul

In Examples 1 to 7, the emission wavelength of Mn ²⁺ is shifted to longer side by the addition of the Group XIII element and shows emission in the red region of 600 nm or higher when manufactured to the dispersion-type EL device. In particular, in Example 6, since the stress applying time by the ball mill is lengthened, high density stacking fault frequency becomes high such that planar stacking faults at intervals of 5 nm or less are 10 or more, and EL emission strength can be heightened. The main factor of this fact is presumably for the reason that more Cu ₂ S that are to become electron-generating sources can be present with the increase of stacking faults.

In Example 7, larger particles have grown by making the baking time longer than that in Example 1 and particle size distribution has also been widened. The surface area becomes smaller with the increase of particle size, so that it is thought that the area emitting light becomes smaller and emission strength lowers.

On the other hand, in Comparative Example 1 not containing the Group XIII element, emission is yellow-orange emission of 580 nm, which is seen by doping ZnS with Mn. In Comparative Example 2, where Cu is not added, EL does not show emission. This is considered for the reason that Cu ₂ S for causing electron-generating sources is not present.

Further, In Comparative Example 3, where Mn is not added, chlorines such as NaCl and MgCl ₂ added as fluxes are doped into ZnS to form a DA pair of Cu and Cl, as a result blue-green emission is shown.

Industrial Applicability

As described above, according to the invention, inorganic phosphor materials showing red light emission by dispersion-type inorganic EL can be obtained. The inorganic phosphor materials are useful for the manufacture of a dispersion-type inorganic EL device showing not only red emission but also white emission by combination with other phosphors showing blue-green EL emission.

According to the inorganic phosphor material of the invention, a dispersion- type EL device emitting light in red can be obtained. Further, a dispersion-type EL device emitting white light useful for illumination uses can be obtained by combination of the inorganic phosphor material of the invention and conventionally known phosphors showing blue green EL emission.

This application is based on Japanese patent application JP 2009-075192, filed on March 25, 2009, the entire content of which is hereby incorporated by reference, the same as if set forth at length.