JP2936902B2 - Manufacturing method of EL fluorescent material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent (EL) device which has a sufficiently high luminance and a long life as a practical light emitting device, has a very small variation in characteristics, and has a very high yield and a high yield. A) a method for producing a phosphor;

[0002]

2. Description of the Related Art An EL phosphor is dispersed in an organic dielectric binder and sandwiched between two electrodes, one of which is transparent,
Light is emitted by applying an AC voltage between both electrodes.
The element configured as described above is employed as a thin surface emitting light source in a backlight of a liquid crystal display or the like.

[0003] As an EL phosphor conventionally used, there is a phosphor obtained by activating Cu as an emission center in a zinc sulfide crystal. However, a light-emitting element conventionally manufactured using the phosphor has various improvements since the light-emitting luminance and the light-emitting life are lower than those of other light-emitting elements. Among these, for the improvement of the emission luminance and the life characteristics, the same applicant, after etching the phosphor with an acid, a method of washing with a chelating agent containing an oxidizing agent, and one of acetic acid and sulfuric acid containing the oxidizing agent Alternatively, a method of cleaning by mixing these is proposed. Also, (a) U.S. Pat. No. 3,113,929 discloses a method of improving luminance by heating a phosphor in an oxygen atmosphere, (B) U.S. Pat. No. 5,005,805, and JP-A-61-29608.
No. 5 manufactures a hexagonal (wurtzite type) zinc sulfide phosphor by firing a mixture of zinc sulfide, copper compound, and halide at 1100 to 1200 ° C. In addition, a method of subjecting a phosphor converted to a cubic (sphalerite type) having better luminance and life characteristics than a hexagonal type to open annealing (700 to 950 ° C.) in the air, (c) Japanese Patent Laid-Open No. 2-94
No. 287 discloses a method of treating a phosphor with ozone that is more active than oxygen to form an oxygen layer on the phosphor surface layer and improve the life characteristics.

However, even if a phosphor is manufactured by using the above-mentioned manufacturing methods (a) to (c) or the processing method, not only the luminance and the life characteristics are insufficient as a practical light emitting element but also the characteristics are not sufficient. Since the dispersion is large and the production yield and yield are poor, the production cost is high, and it is difficult to provide a phosphor that meets market requirements.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present inventors
First, in order to solve the above-mentioned problems, the following known production methods, namely, (1) zinc sulfide, a copper compound, and alkali metal chlorides, alkaline earth metal chlorides as fluxes (grain growing agents), and chlorides, are used. A halide such as ammonium is mixed and fired at 1100 to 1300 ° C. in a crucible with a closed lid to grow particles having an average of about 30 μm required for the phosphor. (2) Next, the wurtzite type obtained by this firing By applying mechanical stress (mechanochemical effect) using a ball mill or the like to the ZnS crystal, the ZnS crystal is converted into a zinc-blende ZnS crystal form having more excellent luminance and life characteristics. The above (a) to (c) are based on a manufacturing process consisting of a method of annealing at 950 ° C.
I reviewed it again, including the technology, and tried to consider it.

However, the above-mentioned production method has particularly poor life characteristics, and it has not been possible to obtain a phosphor having high luminance and long life characteristics which can be practically used. Especially in the conventional manufacturing method, the above (3)
In the step (3), the phosphor is annealed in the air in a crucible with an open lid, so that ZnS is oxidized and decomposed to change to ZnO, so that the yield and the yield of the phosphor are extremely deteriorated. The body has a large variation in phosphor characteristics due to different oxygen partial pressures in the upper and lower parts of the crucible, and a large amount of toxic SO ₂ acid gas is generated during firing.
It has been found that there are numerous problems, such as environmental and sanitary problems, and deterioration of the firing furnace due to the generated gas.

Therefore, the first point of the present invention is to prevent the phosphor from being affected by atmospheric oxygen during refiring.
As a result of studying a method of improving the characteristics by firing in a closed crucible with a lid (so that a large amount of ZnO and SO ₂ gas is not generated), zinc sulfate, barium sulfate, and strontium sulfate were used as a sulfate in the phosphor. Or a mixture thereof and annealed at 550-900 ° C., yield
It has been found that the yield is extremely high, and a stable, high-brightness, long-life phosphor free of toxic SO ₂ acid gas during firing and having little variation in characteristics can be obtained.

As a second point of view, a simple low-temperature heat treatment is performed in order to develop superior brightness and life characteristics without performing a special process such as ozone treatment after etching the phosphor surface layer. The means to improve the characteristics by the method were studied. In other words, Zn-S bonds are broken on the surface of the phosphor subjected to the etching treatment, the surface energy is high and the state is very unstable, and the lattice damage of the crystal occurs near the phosphor surface due to damage by etching. This has a significant adverse effect on the characteristics.
Therefore, the heat treatment was performed at low temperature in the air to moderately oxidize this surface layer to reduce surface energy and recrystallize lattice irregularities near the surface. As a result, it was found that the luminance and the life characteristics were significantly improved by performing the heat treatment in the air at 90 to 160 ° C. for 25 to 250 hours after etching the phosphor surface layer.

The present invention provides a method for manufacturing an EL phosphor which solves the conventional problems based on the above-mentioned idea.
The EL phosphor produced by this method has an initial luminance of 25% and a luminance half-life of 80% as compared with those using a conventional production method.
Develop improved properties. Further, in the present method, the dispersion of the phosphor characteristics is extremely small, the yield and the yield are extremely high, the production cost is reduced, and the toxic SO ₂
An excellent manufacturing method without generation of an acid gas is provided.

[0010]

According to the present invention, there is provided a process for sintering a mixture containing zinc sulfide, a copper compound and a chloride to produce an intermediate phosphor, and re-sintering after applying a mechanical stress to the intermediate phosphor. Wherein the re-firing step is performed at 550-900 ° C. by mixing sulfate, shutting off the atmosphere, and further obtained after the re-firing step. After etching the phosphor surface layer,
A method for producing an electroluminescent phosphor, comprising a step of performing a heat treatment at 90 to 160 ° C. for 20 to 250 hours in the air.

In a preferred aspect of the present invention, the sulfate is one of zinc sulfate, barium sulfate, and strontium sulfate, or a mixture thereof.

The method for producing an EL phosphor according to the present invention comprises:
Copper compounds such as copper acetate (Cu concentration 0.03-
0.12% by weight) and dried, and at least one of an alkali metal chloride, an alkaline earth metal chloride and ammonium chloride as a flux is added to the mixture in an amount of 6 to 100%.
% In a crucible with a lid closed, 1100-1300 ° C,
It is baked for 2 to 10 hours to grow particles having an average of about 30 μm required for the phosphor. Next, the fired phosphor is washed several times with ion-exchanged water and dried.

The ZnS: Cu,
Cl phosphor is mostly wurtzite type ZnS crystal (hexagonal)
Therefore, the zinc-blende type Z having more excellent brightness and life characteristics
Since it is necessary to convert to the nS crystal form, sufficient mechanical stress is applied so that the phosphor particles are not crushed using, for example, a ball mill.
(Mechanochemical effect). This phosphor has 11
Since it is fired at a high temperature of 00 to 1300 ° C., a large number of vacancies are generated in the bulk crystal due to the volatilization of sulfur, which causes the life characteristics to be greatly reduced. In addition, crystal damage is large because mechanical stress is applied,
A cause for lowering the light emission and life characteristics is added.

For this reason, in the next stage, the sulfur vacancies in the ZnS bulk crystal are removed, and a sulfate is added to remove the crystal damage, and the ZnS bulk crystal is refired in a closed crucible with a lid. At this stage, the sulfur vacancies in the crystal were replaced with S or O (both of the same family elements) by the sulfate SO ₄ ^2- ions in the sulfate immobilized in the closed crucible, and the heat treatment at this time Recrystallized.

As sulfates, zinc sulfate, barium sulfate,
It is appropriate to add one kind of strontium sulfate or a mixture thereof to the phosphor in an amount of 5 to 25% by weight. If the amount of sulfate is less than 5% by weight, S vacancies cannot be sufficiently removed, so that there is no effect. If the amount is too large, the load of disposal processing (etching) in the processing step after firing increases, which is not preferable. Refiring temperature is 1-2 in the range of 550-900 ° C.
It is appropriate to bake for 0 hours. If the temperature is lower than 550 ° C., the diffusion of S and O becomes insufficient and the S vacancies in the crystal cannot be removed, so that there is no effect. Absent.

Next, the phosphor after firing is subjected to an etching process which is generally performed to remove lattice irregularities and excessive Cu _x S (X = 1 to 2) of crystals contained in the phosphor surface layer. However, the surface of the phosphor after the treatment is broken, the bond of Zn-S is broken, and the surface energy is high and the phosphor is in an extremely unstable state. In addition, the lattice damage of the crystal occurs again near the phosphor surface due to the etching damage, which affects the life characteristics. Therefore, in the next stage, a low-temperature heat treatment in the air is performed to moderately oxidize the phosphor surface to reduce the surface energy and recrystallize the lattice irregularity of the crystal near the phosphor surface.

The above low temperature heat treatment temperature is 90 to 160 ° C., preferably 100 to 150 ° C.
0-250 hours is appropriate. When the treatment temperature is lower than 90 ° C., recrystallization of the crystal lattice irregularity existing on the phosphor surface is insufficient, so that there is no effect. Has no effect because it increases. Regarding the processing time, whether the processing time is shorter than 20 hours or longer than 250 hours, each has the same effect as described above, which is not preferable.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on specific embodiments. 1 kg of zinc sulfide and 1.55 g of copper acetate dihydrate were wet-mixed with ion-exchanged water and dried at 125 ° C. for 20 hours. Next, 8 g of barium chloride dihydrate and 10 g of magnesium chloride hexahydrate were used as fluxes in 200 g of this mixture.
6 g of sodium chloride was mixed, put into a 280 cc crucible made of alumina, covered with a lid, and fired in the air at 1200 ° C. for 4 hours. After firing, the fired material was washed five times with 2 liters of ion-exchanged water to dissolve and remove the flux, and filtered to remove 13%.
Dry at 0 ° C. for 15 hours. Next, 150 g of this phosphor was
Then, 150 g of an alumina ball φ10 mm was put in a polyethylene liter pot, and a lid was put thereon. The lid was rotated on a ball mill rotating table at 600 rpm for 120 minutes. This phosphor was converted to cubic ZnS by X-ray diffraction. Next, 100 g of this phosphor and 15 g of zinc sulfate as a sulfate,
5 g of barium sulfate and 5 g of strontium sulfate are mixed,
The mixture was placed in a 150 cc crucible made of alumina, capped, and refired in the air at 800 ° C. for 5 hours. Next, after firing, the phosphor was taken out of the crucible, placed in a 20% acetic acid aqueous solution, washed with stirring at a temperature of 80 ° C. for 1 hour, and then washed 7 times with 2 liters of ion-exchanged water. After filtration, remove 1 phosphor
As a result of heat treatment at a temperature of 10 ° C. for 100 hours, the yield was 91%.
Was obtained.

Evaluation of the luminance and life characteristics of the phosphor was carried out by kneading the phosphor with cyanoethyl cellulose and screen-printing it on a transparent polyethylene film electrode on which ITO (tin-doped indium oxide) was deposited to form a 50 μm light-emitting layer. Subsequently, cyanoethyl cellulose kneaded with barium titanate was screen-printed thereon to form a 20 μm insulating layer, and finally a silver paste was applied thereon to form a back electrode. Next, drying was performed at 100 ° C. for 3 hours, and further vacuum drying was performed at 85 ° C. for 15 hours. Terminals were attached to electrodes, and vacuum thermocompression bonding was performed using a moisture-proof film made of ethylene trifluoride chloride to form an EL light emitting device. Characterization, at room temperature, 120V, a result of applying an AC voltage of 1 kH _z between the electrodes of the EL light emitting element, in an open crucible without adding a conventional sulfate, compared to phosphor and calcining in air As a result, a light emission luminance of 251 cd / m ² and a luminance half life of 3180 hours are exhibited. In the method of the present invention, the light emission luminance is 25% and the luminance half life is 8% as compared with the phosphor prepared by the conventional method.
The properties improved by 0% were exhibited.

[0020]

[Comparative Example] As a result of characteristic evaluation of a phosphor manufactured in exactly the same manner as in the above example except that the low-temperature heat treatment temperature was changed, when the heat treatment temperature was lower than 90 ° C or higher than 160 ° C, the brightness and Little improvement in life characteristics was observed.

Further, in the method of the present invention, the behavioral relationship of the luminance and the life characteristics when the heat treatment temperature is 100 ° C. and 150 ° C., respectively, for 1 to 400 hours is shown in the graphs of FIG. 1 and FIG. Life curve (A) and brightness curve
As shown in (B), the condition of the heat treatment in the air is 20 to 250.
The properties improve significantly with time. In addition, as a comparative example, in the above method, the characteristics of the case where ZnS: Cu, Cl phosphor was refired in the air in a crucible in which the lid was opened without adding a sulfate (conventional method) are shown in graphs in FIGS. Indicated. Clearly, the effect of improving the luminance and life characteristics was not recognized.
From this experimental result, it can be seen from the experimental results that the phosphor of the present invention is not oxidized and decomposed at the time of calcination as compared with the conventional method, so that a large amount of toxic SO ₂ acidic gas is not generated, and the final yield of the phosphor is always 88. In the conventional method shown in the comparative example, ZnS was obtained in a crucible whose lid was opened at the time of firing.
Cu and Cl phosphors are oxidatively decomposed to refire in the air,
A large amount of toxic SO ₂ acid gas is generated and is constantly 62-68
% Low yield.

[0022]

According to the method of the present invention, the emission luminance is 25% and the luminance half-life is 80% as compared with the phosphor prepared by the conventional method.
%. Further, the present method provides an excellent production method in which the variation in characteristics is extremely small, the yield and the yield are high, the production cost is reduced, and no corrosive gas or toxic gas is generated during firing.

[Brief description of the drawings]

FIG. 1 shows the relative luminance of a phosphor (heat treatment temperature of 150 ° C.) manufactured by the method of the present invention with respect to the heat treatment time (h).
Graph showing (B) and relative luminance half-life (A).

FIG. 2 shows the relative luminance of the phosphor (heat treatment temperature: 100 ° C.) manufactured by the method of the present invention with respect to the heat treatment time (h).
Graph showing (B) and relative luminance half-life (A).

FIG. 3 is a graph of relative luminance (D) and half-life (C) of a phosphor (heat treatment temperature: 150 ° C.) manufactured by a conventional method.

FIG. 4 is a graph of relative luminance (D) and half-life (C) of a phosphor (heat treatment temperature: 100 ° C.) manufactured by a conventional method.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C09K 11/56 CPC C09K 11/08

Claims (2)

(57) [Claims] 1. A fluorescent light comprising a step of firing a mixture containing zinc sulfide, a copper compound, and a chloride to produce an intermediate phosphor, and a step of applying a mechanical stress to the intermediate phosphor and then refiring the intermediate phosphor. The method of manufacturing a body, wherein the refiring step is performed at 550 to 900 ° C. by mixing sulfate and shutting off the air, and further, after the refiring step, etching the surface layer of the obtained phosphor. After treatment, in air, 90-160 ° C
A method for producing an electroluminescent phosphor, comprising a step of performing a heat treatment for 20 to 250 hours. 2. The method for producing an electroluminescent phosphor according to claim 1, wherein the sulfate is one or a mixture of two or more of zinc sulfate, barium sulfate, and strontium sulfate.