JP2006089594A - Electroluminescent phosphor and method for producing the same, and electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an electroluminescent phosphor capable of producing a high-luminance particle-dispersion type EL element. <P>SOLUTION: The method for producing an electroluminescent phosphor comprises the steps of firing a mixture comprising zinc sulfate, a copper compound and a halide to produce an intermediate phosphor, applying impulsive force to the intermediate phosphor to introduce a dislocation line, and re-firing the intermediate phosphor in which the dislocation line is introduced. The method for producing an electroluminescent phosphor further comprises the step of mixing at least one of the organic materials selected from carboxylic acids, mercaptans and polyethylene glycols to the phosphor after the re-firing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electroluminescence element, an electroluminescent phosphor used therefor, and a method for producing the same.

A dispersive electroluminescence (hereinafter also referred to as “EL”) element is a light-emitting element in which an electroluminescent phosphor is sandwiched between electrodes. Generally, an electroluminescent phosphor powder is dispersed in a binder having a high dielectric constant. In this structure, at least one of the electrodes is sandwiched between two transparent electrodes, and light is emitted by applying an alternating electric field between the two electrodes. As electroluminescent phosphor powder (EL phosphor powder) used in the dispersion type EL element, zinc sulfide as a base material, activator such as copper (metal ion as emission center) and coactivator such as chlorine are added. What has been manufactured is widely known. However, this light emitting device has a drawback in that the light emission luminance is lower than the light emitting device based on other principles. For this reason, various improvements have been attempted conventionally.
In order to increase the luminance of the EL phosphor, it is conceivable to increase the number of electron generation sources in the phosphor particles. In the case of phosphors doped with zinc sulfide as an activator, zinc sulfide is subjected to mechanical impacts such as ball mill, hydrostatic pressure, and ultrasonic waves to introduce dislocation lines, followed by sulfurization along stacking faults during the subsequent firing process. Copper needle crystals, that is, electron generation sources can be formed (for example, Patent Documents 1 and 2). Therefore, the number of electron generation sources increases as the impact time and strength increase. However, these impacts simultaneously introduce defects in the particles that become inefficient processes, resulting in a decrease in EL luminance.

On the other hand, several methods for improving the performance of phosphors by adsorbing organic substances on the surfaces of the phosphor particles to improve the surface have been reported. For example, in Patent Document 3, a substance B (for example, an amine compound) that treats the phosphor surface with a compound A (for example, a coupling agent) having a functional group a (for example, an epoxy group) and then reacts with the functional group a. A method of coating an organic substance by reacting by dispersing in is disclosed.
In addition, the phenomenon that the photoluminescence intensity is increased by adsorbing carboxylic acid on the surface of nano-sized particles doped with manganese as an activator for zinc sulfide is well known and has been reported in many papers. For example, Non-Patent Document 1 reports that the photoluminescence intensity has been doubled by adsorbing polyacrylic acid on the surface of a phosphor particle having a particle diameter of 2 nm in which zinc sulfide is doped with manganese.
However, adapting the surface modification method by adsorbing organic substances on the surface of the above-mentioned conventional phosphor particles to particles into which defects that become inefficient processes are introduced is that the introduced defects are recombined during EL driving. It was considered difficult because it released a large amount of heat at the center and decomposed organic matter.
Japanese Patent Laid-Open No. 61-296085 JP-A-6-306355 JP 2002-88357 A Toyoda et al. (Taro Toyoda, Alamira B. Cruz), Thin Solid Films, 438-439 (2003), 132-136

  It is an object of the present invention to provide a high-luminance particle-dispersed EL device, an electroluminescent phosphor capable of manufacturing the EL device, and a suitable manufacturing method thereof.

As a result of intensive studies on the above problems, the present inventors have modified the phosphor particle surface included in the dispersion-type EL element with an organic substance, thereby reducing inefficiency processes occurring on the particle surface and reducing the luminance of the element. I found that it can be improved. The present invention has been made based on this finding.
That is, the present invention
(1) A step of producing an intermediate phosphor by baking a mixture containing zinc sulfate, a copper compound and a halide, a step of introducing a dislocation line by applying an impact force to the intermediate phosphor, and introducing the dislocation line A process for re-firing the intermediate phosphor, and at least one organic substance selected from carboxylic acid, mercaptan, and polyethylene glycol with respect to the phosphor after re-firing. A process for producing an electroluminescent phosphor, characterized by comprising a step of mixing
(2) The method for producing an electroluminescent phosphor according to (1), wherein the organic substance to be mixed is any one of carboxylic acid and mercaptan, or a mixture thereof.
(3) The method for producing an electroluminescent phosphor according to (1), wherein the organic substance to be mixed is polyethylene glycol,
(4) In the step of introducing dislocation lines by applying the impact force, at least one means selected from a ball mill, a hydrostatic pressure, and an ultrasonic wave is used. Any one of (1) to (3) The method for producing the electroluminescent phosphor according to Item,
(5) An electroluminescent phosphor produced by the method for producing an electroluminescent phosphor according to any one of (1) to (4),
(6) The electroluminescent phosphor according to (5), wherein the amount of organic matter adsorbed on the surface of the electroluminescent phosphor is 10% or more of the saturated coating amount,
(7) The electroluminescent phosphor according to (5) or (6), wherein the particle size is 5 μm to 15 μm,
(8) An electroluminescent element having a transparent conductive film, a phosphor layer, an insulator layer, and a back electrode, wherein the electroluminescent phosphor according to any one of (5) to (7) An electroluminescence element characterized by containing, and
(9) The electroluminescent device according to (8), wherein the transparent conductive film has a surface resistance of 0.01Ω / □ to 50Ω / □, and a back electrode made of metal. To do.

  The EL device using the electroluminescent phosphor produced by the production method of the present invention has an excellent effect of emitting light with high luminance.

  One embodiment of the present invention includes a step of producing an intermediate phosphor by firing a mixture containing zinc sulfate, a copper compound and a halide, and a step of introducing a dislocation line by applying an impact force to the intermediate phosphor. A method of producing an electroluminescent phosphor comprising a step of re-firing the intermediate phosphor into which the dislocation lines have been introduced, wherein the phosphor after re-firing is selected from carboxylic acid, mercaptan, and polyethylene glycol And a method for producing an electroluminescent phosphor having a step of mixing at least one organic substance.

  In the step of producing an intermediate phosphor by firing a mixture containing zinc sulfate, a copper compound and a halide, a firing method (solid phase method) widely used in the industry can be used. For example, a zinc sulfide fine particle powder (usually called raw powder) of 10 to 50 nm is prepared by a liquid phase method, and this is used as a primary particle, and a copper compound and a halide are mixed therein, and 900 to 1300 ° C. for 30 minutes. The intermediate phosphor can be manufactured by performing the first baking for 10 hours.

The copper compound used here is used as an activator for the emission center. As the compound, salts such as copper sulfate, copper nitrate and copper chloride are preferable. The addition amount of the copper compound is preferably 0.01 to 0.2% by mass and more preferably 0.05 to 0.15% by mass as a copper element with respect to the base zinc sulfide.
The halide is used as a coactivator, and examples thereof include a chlorine compound, a bromine compound, and an iodine compound. These halides may be used alone or in combination. The amount of halide added varies depending on the type used. For example, in the case of a chlorine compound, 0.01 to 0.3 mass% is preferable as chlorine with respect to the base copper sulfide, and 0.015 to 0.2 mass% is preferable. More preferred.

In the present invention, dislocation lines are introduced by applying an impact force to the intermediate phosphor after the first firing. It is preferable to use at least one means selected from a ball mill, a hydrostatic pressure, and an ultrasonic wave as a means for giving an impact force.
As a method using a ball mill, for example, a glass container having a diameter of 3 to 50 mm is mixed with a sphere for applying an impact and intermediate phosphor fine particles, and an impact is applied at a rotational speed of 30 to 300 rpm for 20 to 720 minutes. It is done.
Examples of the method using hydrostatic pressure include the method described in Japanese Patent No. 2999458.

Next, the intermediate phosphor to which the impact force is applied is refired. In the second baking, for example, heating is performed at 500 to 900 ° C., which is lower than the first baking, for 1 to 9 hours. These firings cause many stacking faults inside the intermediate phosphor. It is preferable to appropriately select the conditions for the first firing and the second firing so that more stacking faults are included in the intermediate phosphor particles.
Thereafter, the intermediate phosphor particles are etched with an acid such as hydrochloric acid to remove the metal oxide adhering to the surface, and the copper sulfide adhering to the surface is removed by washing with KCN and dried. .

  Subsequently, at least one organic material selected from carboxylic acid, mercaptan, and polyethylene glycol is mixed with the phosphor after recalcination, and the phosphor particles are surface-treated to obtain an electroluminescent phosphor. Here, as the carboxylic acid, for example, polyacrylic acid, succinic acid, citric acid, oleic acid, malic acid, malonic acid, linoleic acid, linolenic acid, maleic acid, formic acid, acetic acid, propionic acid, stearic acid, lactic acid, butyric acid Oxalic acid, aconitic acid, docosahexaenoic acid, eicosapentaenoic acid, isophthalic acid, terephthalic acid, benzoic acid, lauric acid and the like, and polyacrylic acid, succinic acid and citric acid are preferred. Examples of mercaptans include propyl mercaptan, isopropyl mercaptan, n-butyl mercaptan, allyl mercaptan, benzyl mercaptan, mercaptosuccinic acid, mercaptoacetic acid, mercaptoxylene, mercaptoaniline, mercaptocyclohexane, mercaptophenol, 3-mercapto-1-propanesulfone. Acid, 3-mercaptopropionic acid, and α-mercaptopropionic acid, and mercaptosuccinic acid and mercaptoacetic acid are preferred. Carboxylic acid, mercaptan, and polyethylene glycol suppress heat generation and prevent decomposition in order to improve luminous efficiency.

Examples of the method of mixing the organic material include a method in which the re-fired intermediate phosphor is put into an organic aqueous solution and stirred at room temperature. The processing conditions such as the concentration of the organic substance in the aqueous solution, the amount of the aqueous solution, the input amount of the intermediate phosphor, the stirring temperature, and the stirring time are such that the adsorption amount of the organic substance on the surface of the electroluminescent phosphor is 10% or more of the saturated coating amount. It is preferable to set as appropriate.
The coverage of the adsorbate on the surface of the electroluminescent phosphor particles is preferably 10% or more, and more preferably 50% or more. The amount of adsorbate adsorbed on the surface of the electroluminescent phosphor particles can be obtained from the peak intensity such as C = O of FTIR, for example. The saturation coating amount can be determined from the addition amount at which the peak intensity of FTIR does not increase even when the addition amount of the adsorbate is increased. The coverage can be obtained by taking the ratio of the peak intensity of FTIR obtained in the case of an arbitrary addition amount to the peak intensity of FITR at this time. If the coverage of the adsorbate is too small, it may not be possible to reduce the inefficient process.

  Another embodiment of the present invention is an electroluminescent phosphor produced by the above production method. The electroluminescent phosphor preferably has a particle size of 5 μm to 30 μm, more preferably 5 μm to 15 μm. If the particle size is too large, the thinning of the device will be hindered. If the particle size is too small, the recombination process will increase and the luminous efficiency will decrease.

  Yet another embodiment of the present invention is an electroluminescent device having a transparent conductive film, a phosphor layer, an insulator layer, and a back electrode, wherein the phosphor layer contains the electroluminescent phosphor described above. is there.

  As the transparent conductive film, a film formed of any material generally used as a transparent electrode of an EL element can be used. For example, ITO (indium tin oxide), tin-doped tin oxide, antimony-doped tin oxide, zinc-doped tin oxide and other oxides, a multilayer structure in which a silver thin film is sandwiched between high-refractive index layers, and π conjugates such as polyaniline and polypyrrole Based polymers. These transparent conductive films are preferably provided with a comb-like or grit-type fine metal wire to improve the conductivity. The surface resistance of the transparent conductive film is preferably 0.01Ω / □ to 50Ω / □, and more preferably 0.01Ω / □ to 30Ω / □.

As the phosphor layer, a material obtained by dispersing the above electroluminescent phosphor in a binder can be 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 analyzer, or the like can be used.

  The phosphor layer is continuously applied on a plastic support with a transparent electrode, using a slide coater or an extrusion coater, so that the dry film thickness of the coating film is in the range of 10 μm to 60 μm. It is preferable to do. At this time, the film thickness variation of the phosphor layer is preferably 12.5% or less, particularly preferably 5% or less.

The insulator layer is also referred to as a dielectric layer, and any material can be used as long as it has a high dielectric constant and insulation and has a high dielectric breakdown voltage. These are selected from metal oxides, nitrides and sulfides. 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. In the case of a uniform film, the dielectric film may be prepared by a vapor phase method such as sputtering or vacuum deposition. In this case, the thickness of the film is usually in the range of 0.1 μm to 10 μm. The insulator layer is preferably adjacent between the phosphor layer and the electrode.

For the back electrode on the side from which light is not extracted, any material having conductivity can be used. For example, it is appropriately selected from gold, silver, platinum, copper, iron, aluminum and other metals, graphite, etc. depending on the form of the element to be created, the temperature of the production process, etc. The transparent electrode may be used.
In the present invention, it is preferable that the transparent conductive film has a surface resistance of 0.01Ω / □ to 50Ω / □, and the back electrode is made of metal.
Also, both the transparent conductive film and the back electrode can be applied using the above-described slide coater or extrusion coater by preparing a conductive material-containing coating solution in which the conductive fine particle material is dispersed together with a binder.

  In addition, in the element configuration of the present invention, various protective layers, filter layers, light scattering reflection layers, and the like can be provided as necessary.

  Hereinafter, the present invention will be described in more detail based on examples.

Example 1
To 250 g of dry powder of zinc sulfide (ZnS) particles having an average particle diameter of 20 nm added with 0.11 mol% of copper sulfate to zinc sulfide, 20 g of sodium chloride (NaCl) powder as a flux, barium chloride (BaCl ₂ .2H). ₂ O) powder and magnesium chloride (MgCl ₂ .2H ₂ O) powder 72.3 g were put in an alumina crucible and fired at 1200 ° C. for 4 hours, followed by washing with water four times, followed by filtration and coagulation with the flux. The phosphor was removed and dried to obtain an intermediate phosphor.
5 g of the obtained intermediate phosphor, 50 g of alumina spheres having an average particle diameter of 0.5 mmφ, and 5 g of zirconia spheres having an average particle diameter of 0.05 mmφ were mixed in a glass container having a diameter of 40 mmφ, and 70 minutes at a rotational speed of 100 rpm. A ball mill impact was applied.
Thereafter, only the sphere was taken out using a sieve and subjected to second baking at 700 ° C. for 6 hours. The particles after calcination were washed by dispersing, settling and removing the supernatant in H ₂ O, and then added with 10% hydrochloric acid to carry out dispersion, settling and removing the supernatant to remove unnecessary salts and dried. Further, a 10% KCN solution was heated to 70 ° C. to remove Cu ions and the like on the surface. The average particle size of the phosphor thus obtained (phosphor particle A) was 27 μm.
3 g of the above phosphor particles A were put into 30 cc of a polyacrylic acid (average molecular weight 5000) aqueous solution having a concentration of 0.1% and stirred at room temperature for 60 minutes. After the stirring, the mixture was allowed to stand to precipitate the phosphor particles, and the supernatant was removed. Thereafter, decantation was repeated three times to complete washing with water and dried at 100 ° C. for 2 hours to obtain an electroluminescent phosphor.

BaTiO ₃ fine particles having an average particle size of 0.5 μm are dispersed in a 30 wt% cyanoresin solution, applied onto an aluminum sheet having a thickness of 75 μm so that the dielectric layer thickness is 25 μm, and 120 mm using a hot air dryer. Drying was carried out at 1 ° C. for 1 hour (sheet 1).
The electroluminescent phosphor was dispersed in a cyanoresin solution having a concentration of 30 wt% and coated on a transparent conductive film coated with ITO having a surface resistance value of 30Ω / □. It dried at 120 degreeC for 1 hour using the warm air dryer (sheet | seat 2).
The dielectric layer surface of the sheet 1 and the phosphor layer surface of the sheet 2 were combined and thermocompression bonded. An electrode was attached to this, and sandwiched between moisture-proof sheets having a SiO ₂ layer and thermocompression bonded to obtain an EL element (Sample 1).

Example 2
Example 1 except that the obtained electroluminescent phosphor obtained by modifying the surface of the phosphor particles A by using 5 cc of 0.1 cc polyacrylic acid aqueous solution instead of 30 cc of 0.1% polyacrylic acid aqueous solution was used. An EL device was obtained in the same manner as (Sample 2).

Example 3
Except that 30 cc of 0.1% polyacrylic acid aqueous solution was used as an organic substance and 50 cc of 0.1% polyethylene glycol (average molecular weight 20000) aqueous solution was used to modify the surface of phosphor particles A, exactly the same as Example 1. The EL element was obtained by the method of (Sample 3)

Example 4
An EL device was produced in the same manner as in Example 2, except that 30 cc of 0.1% succinic acid aqueous solution was used instead of 30 cc of 0.1% polyacrylic acid aqueous solution as the organic substance, and the surface of phosphor particles A was modified. (Sample 4)

Example 5
The surface of the phosphor particles A was modified by using 40 cc of a 0.1% mercaptosuccinic acid aqueous solution instead of 30 cc of a 0.1% polyacrylic acid aqueous solution as an organic substance. Device was obtained (Sample 5)

Example 6
In Example 1, phosphor particles B having an average particle diameter of 14 μm were obtained by passing the phosphor particles A through a mesh having an aperture of 15 μm.
An EL device was obtained in the same manner as in Example 1 except that the phosphor particles B were used in place of the phosphor particles A (Sample 6).

Comparative Example 1
After performing 10% KCN treatment to remove excess Cu and drying, an EL device was obtained in the same manner as in Example 1 except that no surface treatment was applied to the phosphor particles A (sample) 7).

Comparative Example 2
An EL device was obtained in the same manner as in Example 2 except that polyacrylic acid Na (average molecular weight 5000) was used instead of polyacrylic acid (average particle size 5000) (Sample 8).

Test Example An alternating voltage of 1 kHz to 100 V was applied to the obtained samples 1 to 8, and the luminance was measured. The results are shown in Table 1. Further, the organic coverage was determined from the peak intensity of C = O of FTIR.

As shown in Table 1, compared to Comparative Example 1 in which the surface of the phosphor particles used was not coated with an organic substance and Comparative Examples coated with an organic substance other than that defined in the present invention, the examples of the present invention Also, the luminance of the EL element was high. Further, in all examples in which the coverage of the organic matter was 100%, the luminance of the EL element was 90 cd / m ² or more higher than the comparative example, and excellent light emission characteristics were exhibited.
Furthermore, the sample 6 using phosphor particles having a particle size of 15 μm or less has a luminance of 55 cd / m ² higher than that of the sample 1 using phosphor particles having a particle size of more than 15 μm adsorbed by an organic substance. Even better emission characteristics were exhibited.

Claims (9)

  A step of producing an intermediate phosphor by firing a mixture containing zinc sulfate, a copper compound and a halide; a step of introducing a dislocation line by applying an impact force to the intermediate phosphor; and an intermediate fluorescence having the dislocation line introduced And a step of re-sintering the body, wherein the phosphor after re-sintering is mixed with at least one organic material selected from carboxylic acid, mercaptan, and polyethylene glycol. A process for producing an electroluminescent phosphor, comprising a step.   2. The method for producing an electroluminescent phosphor according to claim 1, wherein the organic substance to be mixed is any one of carboxylic acid and mercaptan, or a mixture thereof.   The method for producing an electroluminescent phosphor according to claim 1, wherein the organic substance to be mixed is polyethylene glycol.   The electric field according to any one of claims 1 to 3, wherein at least one means selected from a ball mill, a hydrostatic pressure, and an ultrasonic wave is used in the step of introducing a dislocation line by applying the impact force. Manufacturing method of light-emitting phosphor.   An electroluminescent phosphor produced by the method for producing an electroluminescent phosphor according to claim 1.   6. The electroluminescent phosphor according to claim 5, wherein the amount of organic matter adsorbed on the surface of the electroluminescent phosphor is 10% or more of the saturated coating amount.   The electroluminescent phosphor according to claim 5 or 6, wherein the particle size is 5m to 15m.   It is an electroluminescent element which has a transparent conductive film, a fluorescent substance layer, an insulator layer, and a back electrode, Comprising: The electroluminescent fluorescent substance of any one of Claims 5-7 is contained in the said fluorescent substance layer. An electroluminescent element characterized.   9. The electroluminescent device according to claim 8, wherein the transparent conductive film has a surface resistance of 0.01Ω / □ to 50Ω / □, and the back electrode is made of metal.