JP2001185358A - Encapsulated fluorescent particle for electroluminescence and el display panel, and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorescent particle which has a high wet-proof and also a high brightness. SOLUTION: An encapsulated fluorescent particle for electroluminescence is composed of fluorescent particle of ZnS 22 and PbTiO3 film 21 of a perovskite crystal structure which covers this fluorescent particle 22. PbTiO3 film 21 has a perovskite structure of a single crystal or multiple crystal and so it has less electrical loss and high dielectric constant. That means it has easier fluorescence particle excitation by electric field as the surrounding dielectric constant of fluorescent particle 22 is higher. Since the brightness of electroluminescence is proportionate to the applied voltage in square or cube, this fluorescent particle can be applied by high voltage. Therefore it has both high wet-proof and high brightness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to encapsulated phosphor particles for electroluminescence (hereinafter, referred to as "EL"), an EL display panel using the same, and an encapsulated phosphor particle for EL. It relates to a manufacturing method.

[0002]

2. Description of the Prior Art Phosphor materials for EL are used in various applications such as flat display panels and decorative articles, cathode ray tubes, and fluorescent lighting equipment. A single crystal, a vapor-deposited fluorescent film, or the like is also used as the EL phosphor material. However, most commonly used is a zinc sulfide (ZnS) phosphor for EL. An EL device that emits light by applying a voltage to a phosphor for EL is different from a dispersive EL device using phosphor particles for EL (hereinafter simply referred to as “phosphor particles”) due to a difference in basic structure. It is divided into a thin film EL device using a body thin film.

[0003] As shown in FIG. 19, a dispersion type EL device is formed by dispersing phosphor particles in a ferroelectric material to form a phosphor layer 54.
This is a kind of parallel plate type capacitor sandwiched between the transparent electrode 43 and the back electrode 46 which does not hinder light emission. The terminal 31 is connected to the transparent electrode 43, and the terminal 32 is connected to the back electrode 46. Between the fluorescent layer 54 and the back electrode 46,
Further, an insulating layer 45 is inserted. Then, by applying a predetermined voltage between the terminal 31 and the terminal 32 through the insulating layer 45, EL light emission is performed. Generally used as this material are ZnS-based phosphor particles 22.

On the other hand, a thin-film EL device is a device in which a phosphor film having a thickness of about 1 μm formed by a vacuum deposition method or the like is used as a light-emitting layer and sandwiched between a transparent electrode and a metal electrode.

In order for an EL device to be of a practical level, phosphor particles must satisfy the following three conditions.

(1) It is excellent in moisture resistance, (2) It is excellent in luminous efficiency, and (3) It is easy to be excited by an electric field.

The first condition is an essential condition for realizing a highly reliable and stable EL device because the emission intensity of the phosphor particles rapidly attenuates under high humidity conditions. . For this reason, as shown in FIG. 19, EL devices are generally relatively thick, for example, 25 to 125 μm.
Wrapped in a moisture-proof film 41. Further, a moisture absorbing layer 42 is inserted therein. Further, as shown in FIG. 18, a technique of coating the phosphor particles 22 with a metal oxide thin film 24 has been proposed (see Japanese Patent No. 2756044). As the metal oxide thin film 24, titanium (TiO ₂ )
And titanium / silicon, TiO ₂ / (SiO ₂ ), alumina
(Al ₂ O ₃ ), tin oxide (SnO ₂ ), zirconia (Zr
O ₂ ) and the like are known. Further, the thickness of these metal oxide thin films 24 is about 0.1 to 3.0 μm.

The second condition is a condition that must be satisfied for the entire phosphor particles. For this purpose, there is a luminescent center with good luminous efficiency, or in the case of absorption edge luminescence, the presence of a luminescent center. It is necessary that impurities and lattice defects which hinder the light emitting process be small.

Regarding the third condition, it is important to increase the dielectric constant around the phosphor particles to facilitate excitation by an electric field. Further, since the brightness of EL is generally proportional to the second to third power of the applied voltage, it is desirable that the voltage applied to the phosphor particles be as high as possible. Therefore, it is extremely important to cover the phosphor particles with a ferroelectric material having a high dielectric constant and a small electric loss.

In ferroelectric materials, displacement type ferroelectrics, particularly perovskite type ferroelectrics, are very important. A representative example is barium titanate (BaTi
O ₃ ). At sufficiently high temperatures, the crystals are completely cubic, but below a certain temperature, Ti ⁴⁺ , Ba
^{The 2+} positive ion is displaced relative to the O ²⁻ negative ion to cause spontaneous polarization and phase transition to tetragonal. This phase transition temperature is the Curie temperature. The attraction of spontaneous ion shift can be said to be a dipole interaction amplified by the local electric field. Since the perovskite ferroelectric has three polarization axes, a material having properties comparable to that of a single crystal can be produced by polarization processing in a sintered body. BaTiO
No. ₃ has several problems such as a high firing temperature and a large change in relative dielectric constant with time.

The "sol-gel method" starts from a solution state of a metal organic or inorganic compound, and the solution is subjected to hydrolysis / polycondensation reaction of the compound in the solution to form a sol in which fine particles of metal oxide or hydroxide are dissolved. Then, the reaction is further advanced to gel. This is a method of heating the porous gel thus formed to form an oxide solid. The oxide solid to be synthesized is mainly composed of glass (amorphous ceramics), but also includes a polycrystalline material (so-called ceramics) made through an amorphous phase.

[0012] The invention of the sol-gel method has been vigorously carried out because of the conventional melting method (the raw material powder is heated to 1500 ° C).
This is because it has the following excellent characteristics as compared with the above-mentioned method in which the liquid is heated and melted at a high temperature to obtain a liquid, which is cooled to obtain a glass body).

(1) If the conditions are selected, glass can be synthesized at a much lower temperature than the melting method, and ceramics can be sintered more densely than in the case of using conventional raw materials.

(2) Since starting from a solution, raw materials are mixed at a molecular level and an atomic level in a multi-component system, the overall homogeneity is increased in glass, and all particles in a multi-component polycrystalline ceramic have a desired composition. Will have.

(3) Due to crystallinity and phase separation, it is possible to vitrify a composition that does not form a homogeneous glass by the conventional glass melting method. In addition, in the case of multi-component polycrystalline ceramics, since the components are homogeneously mixed at the time of departure, a polycrystalline body having a new composition that cannot be obtained by the method using conventional raw material powders such as carbonates is obtained. be able to.

(4) Since a monodispersed raw material can be produced from fine particles, a high-performance sintered body having a uniform particle size can be produced.

(5) The production efficiency can be increased as compared with the chemical vapor deposition method (CVD method), sputtering, or the like used for synthesizing the functional material. In the CVD method, many fine particles are lost together with the carrier gas without depositing all fine particles in the gas phase. In the liquid phase, since all raw materials may be individual organisms, an improvement in efficiency can be expected.

[0018]

As described above, the conventional dispersed phosphor particles have a disadvantage that they cannot be used for a long time due to deterioration due to moisture in the atmosphere. Further, the conventional dispersion-type phosphor particles have a disadvantage that deterioration due to heat accompanying firing is severe.

In order to use a dispersion type EL device at a low voltage for a long time, it is necessary to facilitate excitation by an electric field. In this regard, as shown in FIG. 19, an insulating layer 45 may be provided around the phosphor particles, and the dielectric constant of the insulating layer 45 may be increased. However, in a conventional dispersion type EL device, a cyanated organic substance such as cyanocellulose is used as a binder, and there are problems such as low luminance and short life in practical use.

On the other hand, some inorganic ferroelectrics have a much higher dielectric constant than organic compounds. For this reason, recently, an attempt has been made to prepare a BaTiO ₃ precursor sol by a sol-gel method, disperse it in phosphor particles, sandwich it between conductive glasses, and fire it as it is. However, in order to obtain a BaTiO ₃ thin film having good crystallinity, a high temperature of 600 ° C. or more is necessary.
This caused decomposition of the ZnS phosphor particles.

Accordingly, an object of the present invention is to provide phosphor particles having high moisture resistance and high luminance.

Another object of the present invention is to provide an inexpensive EL display panel having a simple structure.

Still another object of the present invention is to provide a lead-based perovskite compound thin film having a high relative dielectric constant and excellent homogeneity on a surface of phosphor particles for an EL at a low temperature. An object of the present invention is to provide a method for producing phosphor particles.

Still another object of the present invention is to provide an encapsulated EL fluorescent material capable of coating a lead-based perovskite compound thin film having good crystallinity on the surface thereof while preventing deterioration of the base phosphor particles. An object of the present invention is to provide a method for producing body particles.

[0025]

A first feature of the present invention is as follows.
EL phosphor particles encapsulated are composed of phosphor particles and a thin film of a lead-based perovskite compound having a crystal structure that covers the phosphor particles. “Crystal structure” is a perovskite-type crystal structure. The “lead-based perovskite compound” according to the first feature of the present invention includes:
It is represented by the general formula A (B′B ″) O ₃ and Pb is added to the A site.
At the B site is a compound represented by a combination of elements that can be tetravalent by a combination of divalent, pentavalent, divalent, hexavalent, and the like. Since these materials have unique material characteristics alone and different temperature characteristics such as Curie temperature and relative permittivity, it is possible to synthesize materials having various temperature characteristics depending on the combination. A typical example of the “lead-based perovskite compound” is lead titanate (PbTiO ₃ ). PbTiO ₃ has a Curie temperature of 490 ° C.
And a ferroelectric material having a relatively small relative dielectric constant. PbTi
O ₃ has the largest lattice anisotropy (c / a) of 1.064 as a perovskite-type ferroelectric, and has a long axis of C 3.
It has large spontaneous polarization, pyroelectricity, and piezoelectricity in the axial direction.

In ordinary ceramics, the direction of polarization cannot be aligned because the crystal axis direction of each crystal grain is not oriented, and all the properties of the material cannot be brought out. However, as a lead-based perovskite compound thin film, In the case of forming, since the crystal grains are sequentially laminated and grown on the substrate, by appropriately selecting the substrate, it is possible to form an alignment film and an epitaxial film in which the crystal axes are aligned. Thus, a large electric field can be applied to the film through a relatively large area. The lead-based perovskite compound thin film according to the first aspect of the present invention has a single crystal or polycrystalline perovskite structure, and thus has a small electric loss and a high relative dielectric constant. That is, since the specific permittivity around the phosphor particles is high, the excitation of the phosphor particles by the electric field is efficient and easy. Since the brightness of the EL is generally proportional to the second to third power of the applied voltage, a high voltage can be applied to the phosphor particles according to the first feature of the present invention. Therefore, high luminance can be realized at the same time as high humidity resistance.

As the phosphor particles according to the first feature of the present invention, ZnS particles are typical. The thickness of the lead-based perovskite compound thin film is preferably about 0.5 μm to 3 μm. When the thickness of the lead-based perovskite compound thin film 21 is 0.
If the thickness is less than 5 μm, the moisture resistance becomes insufficient. Also,
When the thickness is more than 3 μm, cracks are easily generated, which is not preferable.

A second feature of the present invention resides in that a back electrode, a fluorescent layer disposed above and in contact with the back electrode, and a fluorescent layer disposed above and in contact with the fluorescent layer. An EL display panel comprising transparent electrodes. Here, the “fluorescent layer” is composed of the encapsulated phosphor particles for EL according to the first feature of the present invention.

As described above, the lead-based perovskite compound thin film having a crystal structure according to the first feature of the present invention has a high relative dielectric constant. There is no need to apply an electric field. Therefore, the EL display panel according to the second aspect of the present invention does not require an insulating layer as in the related art, has a simple structure, and has a reduced number of manufacturing steps. Therefore, according to the EL display panel according to the second aspect of the present invention, the manufacturing cost can be reduced.

A third feature of the present invention is that (a) a step of preparing phosphor particles, (b) a step of preparing a lead-based perovskite compound precursor, (c) a phosphor particle and a lead-based perovskite compound (D) evaporating a solvent component from the mixture under reduced pressure to form a wet gel of a lead-based perovskite compound containing ZnS phosphor particles, E) a step of drying the wet gel to form a dry gel;
Baking at a firing temperature of 0 ° C. to 490 ° C. at least.

Conventionally, it has been very difficult to synthesize a lead-based perovskite compound single crystal having a sufficient size for practical use. It is considered that the reason why it is difficult to synthesize a single crystal is due to the volatility of lead during processing and the large shrinkage when transforming from cubic to tetragonal. However, in the manufacturing method according to the third aspect of the present invention, a lead-based perovskite compound thin film having a high relative dielectric constant and excellent homogeneity can be easily formed on the surface of the phosphor particles for EL at a low temperature. I can do it. Further, according to the method for producing encapsulated phosphor particles for EL according to the third feature of the present invention, a lead-based perovskite compound thin film having good crystallinity can be formed while preventing deterioration of the base phosphor particles. The surface can be coated.

In the method for producing the encapsulated phosphor particles for EL according to the third aspect of the present invention, the step of firing the dried gel includes a preliminary firing step at 300 ° C. to 400 ° C. It is preferable that this is a two-stage heat treatment step including a main firing step at a high temperature.

In the third aspect of the present invention, it is preferable to use a lead-based perovskite compound precursor sol or a lead-based perovskite compound precursor solution as the lead-based perovskite compound precursor. These precursor sols or precursor solutions are prepared by using ethanol (C ₂ H ₅ OH) as a solvent.
And organic substances such as acetic acid (CH ₃ COOH). According to the TG and DTA measurements of the powder obtained by drying the lead-based perovskite compound precursor sol and the lead-based perovskite compound precursor solution, a weight loss due to thermal decomposition of the organic substance is observed at around 300 ° C. Therefore, in order to sufficiently evaporate the organic matter, in the third aspect of the present invention, 300 ° C. to 400 ° C.
Calcination step (pretreatment) at ℃, more preferably 3
The calcination step (pretreatment) is performed at 50 ° C. 350
When a pretreatment (post-calcination) is performed at 10 ° C. for 10 minutes, the obtained sample has much residual organic matter. Therefore, pretreatment at 350 ° C. for about one hour is preferable.

The firing temperature in the main firing step according to the third aspect of the present invention is preferably from 420 ° C. to 480 ° C. At the firing temperature in the main firing step, electrical degradation of the phosphor particles is slight. For example, ZnS phosphor particles, which are typical phosphor particles, are oxidized by heat treatment at a temperature higher than 500 ° C. to generate ZnO.

In the method for producing encapsulated EL phosphor particles according to the third aspect of the present invention, the lead-based perovskite compound precursor is a lead-based perovskite compound precursor solution having a stoichiometric composition. The firing step is preferably performed at a firing temperature of 450 ° C. for a firing time of 3 hours to 5 hours. Under the conditions of the main firing step, no deterioration due to oxidation or the like of the phosphor particles is observed, and the crystallization of the lead-based perovskite compound proceeds sufficiently, resulting in a perovskite crystal structure. As a result, a lead-based perovskite compound thin film having excellent uniformity of film thickness and uniformity of film quality and high relative dielectric constant can be obtained. According to the SEM observation, the coating of the phosphor particles using the lead-based perovskite compound precursor solution according to the third aspect of the present invention has good uniformity of film thickness and is almost uniformly coated. . Also, the occurrence of cracks is small. However, aggregation can also be confirmed. In addition, in the case of excess lead, the excess amount of lead exists as an oxide, and the X-ray diffraction pattern does not change even if the firing time is increased to 2 hours or 3 hours.

On the other hand, when the lead-based perovskite compound precursor is a lead-based perovskite compound precursor sol having an excess of 20% lead, the firing step is performed at a firing temperature of 450 ° C. for 1 to 5 hours. preferable. But,
When the phosphor particles are coated using the lead-based perovskite compound precursor sol, the obtained sample has a large amount of residual organic substances and a nonuniform film thickness. Therefore, some parts are too thick, and cracks and aggregation are observed. For this reason, some phosphor particles are insufficiently coated. The lead-based perovskite compound precursor sol has a perovskite crystal structure under the condition of 450 ° C. for 1 hour with a lead excess of 20%. According to the X-ray diffraction measurement of the lead-based perovskite compound thin film using the lead-based perovskite compound precursor sol formed by firing under these conditions, the crystal structure of the parent phosphor particles and the crystal structure of the lead-based perovskite compound perovskite Is identified.

[0037]

Next, an embodiment of the present invention will be described with reference to the drawings.

(First Embodiment) As shown in FIG.
Encapsulated EL according to the first embodiment of the present invention
The phosphor particles for use are composed of ZnS phosphor particles 22 and a lead-based perovskite compound thin film 21 having a crystal structure that covers the phosphor particles 22. In the first embodiment of the present invention, the lead-based perovskite compound thin film 21
Is a PbTiO ₃ thin film.

A lead-type pillow according to the first embodiment of the present invention
Buskite compound thin film (PbTiO ₃The thin film 21 is a simple
Having a crystalline or polycrystalline perovskite structure
Low electrical loss and high relative permittivity
You. That is, the relative permittivity around the phosphor particles 22 is high.
Therefore, phosphor particles can be easily excited by an electric field. EL Light
Rusa is generally proportional to the 2nd to 3rd power of the applied voltage.
The phosphor particles according to the first embodiment of the present invention have a high electric charge.
Pressure can be applied. This results in high moisture resistance and high brightness
Degree can be realized.

The PbTi according to the first embodiment of the present invention
The thickness of the O ₃ thin film 21 is selected from about 0.5 μm to about 3 μm. If the thickness of the PbTiO ₃ thin film 21 is less than 0.5 μm, the moisture resistance becomes insufficient. On the other hand, when the thickness is more than 3 μm, cracks easily occur, which is not preferable. Preferably, the thickness of the PbTiO ₃ thin film 21 is in the range of 0.
It is about 8 μm to 1.5 μm. 0.8 μm to 1.5 μ
By selecting a film thickness in the range of about m, it is possible to realize a dielectric constant that is high in moisture resistance and can apply a sufficient electric field to the phosphor particles 22. More preferably, PbTiO ₃
It is preferable that the thickness of the thin film 21 be about 0.9 μm to 1.2 μm. By selecting a thickness of about 0.9 μm to 1.2 μm, the phosphor particles 22 can be made of PbTi having a uniform thickness and a uniform thickness.
It can be coated with the O ₃ thin film 21.

(Second Embodiment) FIG. 2 is a schematic sectional view of an EL display panel according to a second embodiment of the present invention. That is, as shown in FIG.
And a fluorescent layer 44 disposed above and in contact with the back electrode 46 and a transparent electrode 43 disposed above and in contact with the fluorescent layer 44. I have. That is, it has a structure of a kind of parallel plate type capacitor in which the phosphor layer 44 made of the encapsulated phosphor particles for EL shown in FIG. 1 is sandwiched between the transparent electrode 43 and the back electrode 46. The terminal 31 is connected to the transparent electrode 43 serving as the upper electrode of the parallel plate type capacitor, and the terminal 32 is connected to the back electrode 46 serving as the lower electrode. FIG.
Unlike the conventional EL display panel shown in FIG. 9, no insulating layer 45 is inserted between the fluorescent layer 54 and the back electrode 46. That is, the fluorescent layer 44 is in direct contact with the back electrode 46. This is because the lead-based perovskite compound thin film (P) having a crystal structure according to the first embodiment of the present invention is
bTiO ₃ thin film) 21 has a high relative dielectric constant,
This is because the conventional insulating layer 45 is unnecessary. Then, by applying a predetermined voltage between the terminal 31 and the terminal 32, EL emission with high luminance can be performed.

In the EL display panel according to the second embodiment of the present invention shown in FIG. 2, the structure is simple and the number of manufacturing steps is reduced because the conventional insulating layer 45 is unnecessary. Therefore, according to the EL display panel according to the second embodiment of the present invention, the manufacturing cost can be reduced.

The EL display panel according to the second embodiment of the present invention is further wrapped with a moisture-proof film 41 as shown in FIG. We can provide panels. This is because the encapsulated phosphor particles for EL according to the first embodiment of the present invention have high moisture resistance. In FIG. 2, the moisture absorbing layer 4 is provided between the moisture-proof film 41 and the transparent electrode 43.
2 has been inserted. However, since the encapsulated phosphor particles for EL according to the first embodiment of the present invention have high moisture resistance, the moisture absorbing layer 42 may be used for a certain purpose.
Can be omitted. As a result, it is possible to further reduce the thickness and reduce the manufacturing cost.

(Method for Manufacturing Encapsulated EL Phosphor Particles) Next, according to the flowchart shown in FIG. 5, a method for manufacturing encapsulated EL phosphor particles according to the first embodiment of the present invention. Will be described. In order to cover the surface of the ZnS phosphor particles 22 with the lead-based perovskite compound thin film (PbTiO ₃ thin film) 21 having a perovskite crystal structure, in step S301 of FIG. 5, a lead-based perovskite compound (PbTiO ₃ ) precursor sol is used. Alternatively, it is necessary to prepare (adjust) a lead-based perovskite compound (PbTiO ₃ ) precursor solution. Therefore, first, the method for preparing the PbTiO ₃ precursor sol will be described according to the flowchart shown in FIG. 3, and the method for preparing the PbTiO ₃ precursor solution will be described according to the flowchart shown in FIG. P
The bTiO ₃ precursor solution is an adjustment method based on molecular design. In the following, the case of stoichiometric composition and
The case where the percentage is excessive will be described. Therefore, in the following, the numbers in [] are the values when excess lead is used.

First, the method for preparing the PbTiO ₃ precursor sol described in step S301 in FIG. 5 will be described with reference to the flowchart shown in FIG.

(A) As shown in step S101 in FIG. 3, first, 5.72 g (0.015 g) of lead (II) acetate trihydrate (Pb (CH ₃ COO) ₂ ) was placed in a separable flask.
Mol) [6.86 g] and dried at 150 ° C for 5 hours.

(B) Next, as shown in Step S102, 3.6 ml (0.06 mol) of acetic acid (CH ₃ COOH) is added, and the mixture is refluxed at 78 ° C. for 1 hour.

(C) On the other hand, as shown in step S111
In addition, titanium tetraisopropoxide (Ti (iso)
-OC₃H₇)₄4.25 g (0.015 mol)
Acetic acid (CH₃(COOH) 1.8 ml (0.03 mol)
Add and stir for 30 minutes. Further, as shown in step S112
Thus, at room temperature, ethanol (C₂H
₅OH) and stir for 30 minutes.

(D) Next, as shown in step S103, the solutions prepared in steps S102 and S112 are mixed and stirred for 30 minutes. Further, step S1
As shown in FIG. 04, ethanol (C ₂ H ₅ O
H) and stir for 30 minutes.

(E) Then, as shown in step S105, 3 ml of water (H ₂ O ₂ ) is added, and the mixture is stirred for 30 minutes for hydrolysis.

(F) Thereafter, as shown in step S106, 1.53 ml (0.015 mol) of acetylacetone (AcAc) as a stabilizer is added, and the mixture is stirred for 30 minutes.

(G) Finally, as shown in step S106
As described above, ethanol (C₂H ₅OH)
Adjust to 50 ml.

In the above steps (a) to (g), the step of preparing 150 ml of the 0.1 mol PbTiO ₃ precursor sol in step S301 of FIG. 5 has been described.

On the other hand, the method for preparing the PbTiO ₃ precursor solution described in step S301 in FIG. 5 will be described below with reference to the flowchart shown in FIG.

(A) First, as shown in step S201 of FIG. 4, 5.72 g (0.015 g) of lead acetate (II) trihydrate (Pb (CH ₃ COO) ₂ ) was placed in a separable flask.
Mol) [6.86 g] and dried at 150 ° C for 5 hours.

(B) Next, as shown in step S202, Pb (CH ₃ COO) dried in (a) for 5 hours
₂ , 120 ml of absolute ethanol (C ₂ H ₅ OH) was added, and the mixture was refluxed at 78 ° C. for 3 hours while flowing ammonia (NH ₃ ) gas.

(C) On the other hand, as shown in step S211, at the same time as step S202, titanium tetraisopropoxide (Ti (iso-OC ₃ H ₇ ) ₄ ) is 4.2.
5 g (0.015 mol) was taken and absolute ethanol (C ₂ H
₅ OH) is refluxed for 3 hours at 30ml added 78 ° C..

(D) As shown in step S203, the solutions refluxed in step S202 and step S211 are mixed and refluxed at 78 ° C. for 4 hours.

(E) As shown in step S204, 1.53 ml of acetylacetone (AcAc) is added as a stabilizer to the solution obtained in step S203, and the mixture is refluxed again at 78 ° C. for 1 hour.

By the above steps (a) to (e), 0.1 mol of PbTiO ₃ in step S301 in FIG. 5 is obtained.
The process of preparing 150 ml of the precursor solution was described.

Here, in the structure shown in FIG.
1 μm thick PbT for each nS phosphor particle 22
The case where the iO ₃ thin film 21 is covered will be described. In this case, the average particle size of ZnS is 16.47 μm, and ZnS and P
When the mixing ratio with the bTiO ₃ precursor solution (sol) is calculated, [PbTiO ₃ ] / [ZnS] = 0.1351 (1)

Based on the above preparatory description, a method for producing encapsulated EL phosphor particles according to the first embodiment of the present invention will be described below with reference to the flowchart shown in FIG.

(A) As described above, the process proceeds to step S301.
In this case, the lead-based paint is used according to the flowchart shown in FIG.
Lobskite compound (PbTiO₃) Precursor sol, young
In other words, according to the flow chart shown in FIG.
Skyte compound (PbTiO ₃) Prepare the precursor solution
You. At the same time, as shown in step S311, the ZnS
Light body particles 22 are prepared.

(B) Then, in step S302, the phosphor particles and the PbTiO ₃ are mixed at the mixing ratio shown in the equation (1).
Mix the precursor solution (sol).

(C) Further, as shown in step S304, the solvent is evaporated while reducing the pressure at about 78 ° C. using a rotary evaporator. By keeping the rotation number of the rotary evaporator constant, the phosphor particles can be dispersed almost uniformly in the solution (sol). Thus, a wet gel of PbTiO ₃ containing ZnS phosphor particles is obtained.

(D) The PbTiO ₃ precursor sol and the PbTiO ₃ precursor solution thus obtained gradually increase in viscosity when left in a dryer at 80 ° C., and change into a wet gel within several hours. Further, as shown in step S305, the wet gel of PbTiO ₃ containing the ZnS phosphor particles was dried at 80 ° C. for 1 day in a dryer (the gel obtained from the PbTiO ₃ precursor sol contained acetic acid (CH ₃ COOH)). 11
The gel was cracked from the surface by drying at 7 ° C. for 2 days, and the solvents ethanol (C ₂ H ₅ OH) and acetic acid (C
H ₃ COOH) evaporates and is completely dried, yielding a dry gel.

(E) Then, as shown in step S303
As described above, this dried gel is crushed in a mortar and baked under predetermined firing conditions.
Bake. The firing in step S303 is performed at 300 ° C.
To 400 ° C., preferably 350 ° C. for 1 hour.
Process (temporary firing) and then a high-temperature final firing
This is a heat treatment step. Ethanol used as a solvent (C ₂
H₅OH) and acetic acid (CH₃COOH)
PbTiO ₃Precursor sol, PbTiO₃precursor
By measurement of TG and DTA of powder after drying body solution
At around 300 ° C, the weight loss due to thermal decomposition of organic matter was observed.
You. Therefore, in order to sufficiently evaporate organic substances, the present invention
Performs a pretreatment at 350 ° C. 10 at 350 ° C
Minute pre-treatment (post-calcination), the obtained sample
Lots of things. Therefore, at 350 ° C. for one hour,
Preprocessing will be performed on the case. Therefore, step S30
The "predetermined conditions" in 3 means that the pretreatment (temporary firing)
Later, a two-stage heat treatment for main firing at 420 ° C. to 480 ° C.
Refers to the process. Under this condition, the ZnS phosphor particles 22
Has little electrical deterioration. ZnS phosphor particles 22
Is oxidized by heat treatment higher than 500 ° C to produce ZnO
Therefore, a firing temperature of 500 ° C. or more is not preferable. Concrete
Stated more specifically, PbTiO₃Lead 2 for precursor sol
1 hour to 5 at a firing temperature of 450 ° C. with 0% excess
Calcination time is preferred. In particular, at 450 ° C. for one hour
Conditions are preferred. As much as possible, mother ZnS phosphor particles
In order to reduce the deterioration accompanying the firing of 22 itself, PbTiO₃
It is necessary to bake in the shortest baking time to crystallize
This is because that. On the other hand, PbTiO₃For precursor solution
Sets the stoichiometric composition of the dried gel at a firing temperature of 450 ° C.
It is preferable to bake with a baking time of 3 hours to 5 hours.
New Under these conditions, a single perovskite phase is formed.
Because it is PbTiO₃In the case of the precursor solution,
Preferably, the temperature is 450 ° C. for 3 hours. Maternal ZnS
In order to reduce deterioration due to firing of the phosphor particles 22 themselves, P
bTiO₃Baking in the shortest baking time for crystallizing
Is preferred. In case of excess lead, stoichiometric composition
Crystallization starts in a shorter baking time than that of the above. Only
And PbTiO₃The precursor solution should be
It is not preferable because excess lead exists as an oxide. Ma
In addition, as described later, a molecularly designed PbTiO₃precursor
PbTiO on which colloid is deposited is better using body solution₃
The composition is more homogeneous than when a precursor sol is used.

In the present invention, these firing conditions are selected as preferable conditions based on the following results of X-ray diffraction measurement and scanning electron microscope (SEM) observation.

The PbTiO ₃ dried gel obtained from the PbTiO ₃ precursor sol prepared according to the flowchart shown in FIG. 3 was pretreated (pre-baked) at 350 ° C. for 1 hour,
A two-stage heat treatment step of performing main firing at a firing temperature of 450 ° C. and firing times of 10 minutes, 30 minutes, and 1 hour is performed. Lead 20%
Excess dry gel is fired under the same two-step heat treatment conditions. As shown in FIG. 6, the stoichiometric PbTi
According to the O ₃ X-ray diffraction pattern, at a firing temperature of 450 ° C.,
When the sintering time is 10 minutes, most of them are in an amorphous state. In other words, it can be seen that the crystallization is hardly performed in the baking time of 10 minutes. Firing temperature 450 ° C
In the firing time of 30 minutes, a slight perovskite phase can be confirmed, but it is understood that the amorphous portion is large and the crystallinity is not so good. When the sintering temperature is 450 ° C. and the sintering time is one hour, most of the crystallization occurs, and the crystallization peak of oxide (PbO) can be confirmed. On the other hand, lead 20% shown in FIG.
According to the X-ray diffraction pattern of the excess PbTiO ₃ , when the sintering temperature is 450 ° C. and the sintering time is 10 minutes, the amorphous portion is mostly formed and the crystallization is slightly performed. In the baking time of 30 minutes, almost crystallized, but a little amorphous portion is present, and the presence of oxide (PbO) can be confirmed. When the firing temperature is 450 ° C. and the firing time is 1 hour, the perovskite single phase is almost completely formed.

Next, the PbTi ₃ obtained from the PbTiO ₃ precursor solution prepared according to the flowchart shown in FIG.
After calcining the O ₃ dried gel at 350 ° C. for 1 hour,
And a two-stage heat treatment step of performing main firing under the conditions of firing time of 30 minutes, 1 hour, 2 hours, and 3 hours. The dried gel with an excess of 20% lead is fired in the same two-stage heat treatment step.
As shown in FIG. 8, in the case of PbTiO ₃ having a stoichiometric composition, a perovskite single phase can be confirmed in a baking time of 30 minutes, and the presence of an oxide (PbO) can also be confirmed. In the case of PbTiO ₃ having a stoichiometric composition, it was almost crystallized in a firing time of 1 hour, but an oxide was slightly observed. When the firing time is set to 2 hours or 3 hours, the crystallinity is improved, and the perovskite single phase is almost formed in 3 hours. On the other hand, FIG.
According to the X-ray diffraction pattern of PbTiO ₃ having a lead excess of 20% as shown in FIG. 2, a perovskite phase can be confirmed at a firing temperature of 450 ° C. and a firing time of 30 minutes, but an oxide is also present. Firing temperature 450 ° C, firing time 1 hour, 2 hours, 3 hours
In time, a sharp peak of a perovskite single phase can be confirmed, but at the same time, the presence of an oxide can be confirmed. This does not disappear even if the firing time is increased, and has almost the same X-ray diffraction pattern. This is thought to be due to the excess lead being converted into oxide. Therefore, it is not preferable to make the PbTiO ₃ precursor solution excessive in lead.

Further, when coating the PbTiO ₃ thin film 21 with the phosphor particles 22, the ZnS phosphor particles 2
It is also important to avoid that 2 itself deteriorates with firing. FIG. 10 shows the measurement results of X-ray diffraction when the firing temperature was changed to 500 ° C., 550 ° C., and 600 ° C. From the firing temperature of 550 ° C., an X-ray diffraction intensity of 2θ = 36.2 ° is found, and at a firing temperature of 600 ° C., the X-ray diffraction intensity of 2θ = 36.2 ° becomes strong. The X-ray diffraction peak at 2θ = 36.2 ° is a diffraction pattern from the (101) plane of ZnO. FIG.
, The X-ray diffraction peak at 2θ = 28.7 ° was Zn
It is a diffraction pattern from the (008) plane of S.

FIG. 11 is a graph showing the relative intensity of X-ray diffraction of ZnS and the relative intensity of X-ray diffraction of ZnO based on the results of FIG. That is, assuming that the relative strength of ZnS in the state where the heat treatment is not performed is 100%, and the heat treatment temperature is changed between 450 ° C. and 700 ° C., 2θ =
The decrease in the relative intensity of the X-ray diffraction at 28.7 ° is indicated by the solid line.
At a heat treatment temperature of 700 ° C., 2θ = 28.7 ° X
The line diffraction intensity has completely disappeared. And this 70
2θ = 36.2 ° when the heat treatment temperature is changed from 450 ° C. to 700 ° C., assuming that the relative intensity of ZnO in the state where the ZnS peak completely disappears by the heat treatment at 0 ° C. is 100%. The increase in the relative intensity of the X-ray diffraction is shown by a broken line. That is, the broken line indicates that ZnS
5 shows the change in the relative intensity of X-ray diffraction from the (008) plane. From the graph of FIG. 11, under the heat treatment temperature condition of 550 ° C. or more, the base ZnS phosphor particles 22 themselves are oxidized,
It can be seen that ZnO is generated.

FIG. 12 shows the results of X-ray diffraction measurement of the ZnS phosphor particles 22 coated with the PbTiO ₃ precursor sol according to the embodiment of the present invention. From FIG. 12, PbTiO
It can be seen that the crystallized peak of No. ₃ and the peak of ZnS coexist. However, the peak of PbTiO ₃ is not sharp but broad. Further, the obtained powder has a large amount of residual organic substances, and a black portion can be confirmed. On the other hand, PbT
ZnS phosphor particles 2 coated with iO ₃ precursor solution
FIG. 13 shows the X-ray diffraction measurement result of Sample No. 2. As with the case of using the PbTiO ₃ precursor sol, PbTiO ₃ and ZnS
Coexist. The peak of PbTiO ₃ is PbTi
It can be seen that it is sharper and has better crystallinity than that using the O ₃ precursor sol.

As a standard sample, the ZnS phosphor particles 22
Schematic SEM photographs of the unprocessed appearance and surface microstructure
FIG. 14 shows the result. FIG. 14 (a) is 1,800 times.
FIG. 14B corresponds to an SEM photograph of 8,500 times.
I do. As shown in FIG.₃Precursor sol
When used for coating, compared to the standard sample shown in FIG.
One can see a clear difference between the surface microstructure and the appearance. FIG.
(A) is 1,800 times, and FIG. 15 (b) is 8,50 times.
It corresponds to a SEM photograph of 0 times. Therefore, PbTiO ₃Thin film
It turns out that coating with 21 is possible. But gained
PbTiO₃Covered with a thin film 21
You can see which parts are and which are not. Trial
In the portion where the phosphor is coated, the entire phosphor particles 22 are covered.
There are few coverings, and there are many
I can see it. Further, the film thickness is not uniform, and FIG.
Phosphor particles 22 or cracks
Can be confirmed. FIG. 17A is a diagram of FIG.
7 (b) corresponds to a 25,000 times SEM photograph.
PbTiO₃When using a precursor sol, the residual organic matter is high.
A dark portion can be confirmed in the obtained sample. on the other hand,
As shown in FIG.₃Using the precursor solution
When coated, the untreated sample (standard sample) shown in FIG.
From the comparison of PbTiO₃Better coated with thin film 21
You can judge that it has been done. FIG. 16 (a) is 1,800 times.
FIG. 16B corresponds to an SEM photograph of 8,500 times.
I do. PbTiO shown in FIG.₃Using precursor sol
PbTiO₃Coating with thin film 21
Many phosphor particles 22 can be confirmed
You. When comparing the surfaces, the PbTiO shown in FIG.
₃PbTiO2 is better than the sample using the precursor sol.₃precursor
The sample with the solution is
It is being put.

[0075]

According to the present invention, encapsulated phosphor particles for EL having high moisture resistance and high luminance can be provided.

According to the present invention, an inexpensive EL display panel having a simple structure can be provided.

Further, according to the method for producing the encapsulated phosphor particles for EL of the present invention, a PbTiO ₃ thin film having a high relative dielectric constant and excellent homogeneity is coated on the surface of the phosphor particles for EL at a low temperature. You can do it.

Further, according to the method for producing encapsulated phosphor particles for EL of the present invention, a PbTiO ₃ thin film having good crystallinity is coated on the surface thereof while preventing deterioration of the base phosphor particles. I can do it.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an encapsulated phosphor particle for EL according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a display panel using encapsulated phosphor particles for EL according to a second embodiment of the present invention.

FIG. 3 shows PbTiO _{3 according} to the first embodiment of the present invention.
It is a flowchart explaining the preparation method of a precursor sol.

FIG. 4 shows PbTiO _{3 according} to the first embodiment of the present invention.
It is a flowchart explaining the preparation method of a precursor solution.

FIG. 5 shows PbTiO _{3 according} to the first embodiment of the present invention.
5 is a flowchart illustrating a method of coating a ZnS phosphor with a precursor solution (sol).

FIG. 6 is an X-ray diffraction pattern of stoichiometric PbTiO ₃ .

FIG. 7 is an X-ray diffraction pattern of PbTiO _{3 with} a lead excess of 20%.

FIG. 8 is an X-ray diffraction pattern of stoichiometric PbTiO ₃ .

FIG. 9 is an X-ray diffraction pattern of a 20% excess of PbTiO ₃ .

FIG. 10 is a diagram showing a change in an X-ray diffraction pattern when a phosphor particle is subjected to heat treatment between 450 ° C. and 700 ° C.

FIG. 11 is a diagram showing a change in a relative intensity ratio of an X-ray diffraction pattern when a phosphor particle is subjected to a heat treatment between 450 ° C. and 700 ° C.

FIG. 12 shows a PbTiO according to the first embodiment of the present invention.
It is a figure which shows the X-ray-diffraction measurement result of the ZnS fluorescent substance particle | grain coat | covered using ₃ precursor sols.

FIG. 13 shows a PbTiO according to the first embodiment of the present invention.
FIG. 9 is a diagram showing the results of X-ray diffraction measurement of ZnS phosphor particles coated using the _three precursor solutions.

FIG. 14 is a diagram schematically showing an SEM photograph of the appearance and the microstructure of the surface of an untreated state of ZnS phosphor particles.

FIG. 15 shows a PbTiO according to the first embodiment of the present invention.
It is a figure which shows typically the SEM photograph of ZnS coat | covered using ₃ precursor sols.

FIG. 16 shows a PbTiO according to the first embodiment of the present invention.
FIG. 3 is a diagram schematically showing an SEM photograph of ZnS coated using a ₃ precursor solution.

FIG. 17 shows a PbTiO according to the first embodiment of the present invention.
FIG. 4 is a diagram schematically showing an SEM photograph of cracks and aggregation observed on the surface of ZnS coated using No. ₃ ;

FIG. 18 is a schematic sectional view showing the structure of a conventional phosphor particle.

FIG. 19 is a schematic cross-sectional view of a display panel using conventional phosphor particles.

[Explanation of symbols]

21 PbTiO ₃ film 22 phosphor particles 24 metal oxide thin film 31, 32 terminal 41 moisture film 42 wicking layer 43 transparent electrode 44, 54 phosphor layer 45 insulating layer 46 back electrode

Claims (9)

[Claims] 1. Encapsulated phosphor particles for EL, comprising: phosphor particles; and a lead-based perovskite compound thin film having a crystal structure that covers the phosphor particles. 2. The encapsulated phosphor particles for EL according to claim 1, wherein said phosphor particles are ZnS particles. 3. The encapsulated phosphor particles for EL according to claim 1, wherein the thickness of the lead-based perovskite compound thin film is 0.5 μm to 3 μm. 4. A phosphor electrode for EL, comprising a back electrode, phosphor particles, and a lead-based perovskite compound thin film having a crystal structure that covers the phosphor particles. An EL display panel comprising: a fluorescent layer disposed in contact with the back electrode; and a transparent electrode disposed in contact with the fluorescent layer on the fluorescent layer. 5. A step of preparing phosphor particles, a step of preparing a lead-based perovskite compound precursor, and a step of mixing the phosphor particles with the lead-based perovskite compound precursor to form a mixture. Evaporating the solvent component from the mixture under reduced pressure to obtain Zn
A step of generating a wet gel of a lead-based perovskite compound containing S phosphor particles, a step of drying the wet gel to form a dry gel, and a step of firing the dry gel at a firing temperature of 300C to 490C. And a method for producing encapsulated phosphor particles for EL. 6. The baking step is performed at 300 ° C. to 400 ° C.
6. The encapsulated EL according to claim 5, wherein the EL process is a two-stage heat treatment process including a preliminary firing process at a temperature of ° C. and a main firing process at a temperature higher than the preliminary firing process.
Method for producing phosphor particles for use. 7. The firing temperature in the main firing step is 420 ° C. to 4 ° C.
The method for producing encapsulated EL phosphor particles according to claim 6, wherein the temperature is 80 ° C. 8. The lead-based perovskite compound precursor is a lead-based perovskite compound precursor solution having a stoichiometric composition, and the main firing step is performed at a firing temperature of 450 ° C. for a firing time of 3 hours to 5 hours. The method for producing encapsulated phosphor particles for EL according to claim 6 or 7, wherein: 9. The lead-based perovskite compound precursor is a lead-based perovskite compound precursor sol having an excess of 20% lead, and the main firing step is performed at a firing temperature of 450 ° C. for a firing time of 1 hour to 5 hours. The method for producing encapsulated phosphor particles for EL according to claim 6 or 7, wherein: