JPH026589A - Electroluminescent phosphor and electroluminescent element - Google Patents

Abstract

PURPOSE:To provide an electroluminescent phosphor which can give an electroluminescent element having a high luminance and a long life and requiring only a reduced electric power by forming holes having a specified equivalent diameter of the equal projected area circle on the surface of a particle of a zinc sulfide-based phosphor. CONSTITUTION:A mixture of zinc sulfide-based phosphor with an oxide, such as ZnO, Sb2O3, SnO2 or PbO, is heat-treated at 600-900 deg.C and washed with an aqueous solution of a mineral acid, such as hydrochloric, nitric or sulfuric acid, to form holes 2 on the surface of a phosphor particle 1 to increase its specific surface area. In this way, an electroluminescent phosphor having holes 2 of an equivalent diameter 3 of the equal projected area circle or 0.1-2mum on the surface of the phosphor particle 1 and having an excellent efficiency of and electroluminescent luminance per applied voltage and a long half-life of the luminance can be produced. By mixing at least 20wt.%, based on the total phosphors forming a light-emitting layer, this phosphor, an electroluminescent element requiring only a reduced voltage of driving can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an organic dispersed electroluminescent phosphor and an electroluminescent device.

(Prior Art) Electroluminescence (hereinafter referred to as EL) is a luminescence phenomenon that occurs when a high electric field is applied to a phosphor material. Dispersed EL can be roughly divided into enamel type (or inorganic type) and plastic type (
or organic type).

Compared to the former method of mixing EL phosphor in a glass fritter and baking it on an iron plate, the latter method of dispersing EL phosphor in a binder with a high dielectric constant to form a light-emitting layer is thinner, lighter, and lighter. Recently, the latter type has been prized because it can realize any shape and provide high brightness.

FIG. 4 shows a partial cross-sectional view of the basic structure of an organic dispersion type EL element. As shown in the figure, the EL element has an insulating layer (1
3) and a light emitting layer (14) with a back electrode layer (12) made of aluminum foil, InzOz HSnO, and In
, 03-3nO, and a mixed system are sandwiched from above and below by transparent electrode layers (15) made of one or more of the following, and a part of the back electrode layer made of aluminum foil is provided with an electrode lead wire to the outside of the EL element. (18) is connected, and an electrode lead wire (19) to the outside of the EL element is also connected between the other transparent electrode layer and the light emitting layer. Furthermore, the entire structure is covered with protective films (11) and (16) to prevent moisture from entering from the outside.

Although the EL element with the above structure can provide the above-mentioned thin surface emitting element of any shape, it is considerably inferior to other display elements in terms of brightness and lifetime characteristics, so its range of applications is limited. Under these circumstances, various improvements have been made in the past.

For example, cyanoethyl cellulose (Japanese Patent Publication No. 38-82
58), cyanoethyl sucrose, cyanoethyl pullulan, cyanoethylvinyl, and vinylidene fluoride (Japanese Utility Model Publication No. 125668/1983). Furthermore, a method of mixing barium titanate powder in order to increase the dielectric constant (Japanese Patent Application Laid-Open No. 60-216498) is also known.

Furthermore, EL phosphors used in the light-emitting layer are mainly made of II-VI group compounds such as ZnS as the host material, and atoms such as copper, manganese, chlorine, and bromine are added as activators and co-activators. It is a well-known fact that luminescent materials of various colors can be obtained. This ZnS is susceptible to deterioration due to hygroscopic changes caused by moisture during operation of the EL element, resulting in dark spots. Therefore, a method for preventing deterioration of ZnS due to moisture by creating a hygroscopic layer of nylon or the like to prevent moisture from reaching the light emitting layer (Unexamined Japanese Patent Publication) 1986-250
No. 592) and the like are also disclosed.

However, the improvement of the above-mentioned high dielectric constant organic binder and the introduction of nylon to prevent deterioration due to moisture,
From the standpoint of improving the characteristics of an EL element (brightness, lifespan characteristics), it is only a secondary factor, and the improvement of the characteristics of an EL element is largely influenced by the EL phosphor used in the light emitting layer. Therefore, as an improvement over the conventional EL phosphor, the particle size of the phosphor has been increased to about 20 to 30 mm in order to extend the life of the EL phosphor. It is known to increase in size.

However, EL using such large particle size phosphor
The device does not necessarily have a long lifespan because the voltage applied during driving increases and the phosphor deteriorates more quickly.

On the other hand, a proposal was made by the same applicant as the present application (Japanese Unexamined Patent Publication No. 61-2
96085), a method of obtaining a long-life phosphor by making a large-grain hexagonal intermediate phosphor and pressurizing it at high pressure to make a large-grain cubic crystal phosphor; 61
- Obtaining a long-life phosphor by adding a small amount of barium compound before firing as disclosed in Japanese Patent Publication No. 188484 in order to extend its life, and by optimizing the amount of copper as an activator and bromine as a co-activator. (Japanese Unexamined Patent Publication No. 57-145174) methods have been proposed.

(Problems to be Solved by the Invention) In view of the above circumstances, the present invention provides a high-luminance, long-life EL phosphor and the use of this EL phosphor in the light-emitting layer of an EL element, thereby significantly reducing the applied voltage during driving. An object of the present invention is to provide an EL element with high power saving properties.

[Structure of the invention]

(Means and Effects for Solving the Problems) In order to achieve the above-mentioned problems, the present inventors have studied various methods for processing phosphors. the result.

Phosphor and ZnO, 5b20. , 5nOa t PbO
EL
It has been found that vacancies are formed on the particle surface of the phosphor and the specific surface area increases, thereby making it possible to improve the efficiency of EL brightness with respect to applied voltage and to obtain a so-called long-life EL phosphor and EL element with a long half-life period of EL brightness. .

That is, in the present invention, 0.1 to 2. Q, EL with a hole with a diameter equivalent to a projected circle
This EL phosphor is used in the light-emitting layer of an EL element, and is characterized in that the EL phosphor is mixed in at least 20% of the total phosphor forming the light-emitting layer.

As shown in Fig. 2, the projection circle equivalent diameter is
Based on the definition of particle diameter based on the projected image of particles expressed on page 55 of the revised second edition "Powder" publication published on May 12, 1971, the diameter of the opening of the pores was determined. It represents. The numerically limited projection circle equivalent diameter and the proportion of the phosphor having holes in the entire particle are measured based on a photograph taken of an average EL phosphor using an electron microscope (SEM). In the present invention, the base material is zinc sulfide, and contains at least one of copper or manganese as an activator, and at least one of chlorine, bromine, iodine, or aluminum as a co-activator.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

Copper compounds such as copper sulfate (copper concentration 0.02 to 0) are added to zinc sulfide.
．． 2wt%) is made into a slurry, mixed and dried, at least one of alkali metal, ammonia, and alkaline earth metal halide is added to this mixture as a flux.
Mix 10wt%. This mixture is then filled into a quartz crucible, covered, and calcined in air at a temperature in the range of 1100-1200°C for 3-10 hours, washed several times with deionized water after calcination, and dried to give an intermediate fluorescence. Build a body. After heating and pressurizing this intermediate phosphor, Zn is added to the pressurized phosphor.
O, Sb, 0. , SnO,.

One to ten types of oxides such as PbO are mixed in an amount of 3 to 10 wt%.

Next, put this mixture in a crucible, cover it, and heat it to 600 to 900
The heat treatment is carried out in air for 1 to 3 hours at a temperature in the range of °C.

After heat treatment, add acid aqueous solution such as hydrochloric acid, nitric acid, sulfuric acid, etc. to pH 1~
When the cleaning treatment is performed in the range of 0.1 to 2.5 on the particle surface.
0. An EL phosphor having holes with a projection equivalent diameter is obtained.

This EL phosphor is dispersed together with a solvent in an organic binder having a high melting rate such as cyanoethyl cellulose and made into a paste, and then a dielectric material such as barium titanate is coated with a solvent on an aluminum foil that will become the back electrode layer (12). It is dispersed and applied as a paste, and dried to form an insulating layer (13).
The light emitting layer (14) is formed by coating and drying the light emitting layer (14). On the thus obtained aluminum foil substrate, an electrode lead wire (18) is fixed to the end of the aluminum foil on the side opposite to the light emitting layer. On the other hand, In, 03. SnO2, In, 0. -5n
An electrode lead wire (19) is fixed to the conductive side end of the transparent electrode layer (15) coated or vacuum-deposited with a conductive material consisting of one or more of O and mixed systems. After that,
An aluminum foil substrate with the light-emitting layer facing inward and an organic transparent film such as polyester with the transparent electrode layer facing inward are pasted together, and then protective films (11
) and (16) and bonded under pressure to obtain an EL element.

It has been found that such an EL element has characteristics of high brightness, long life, and high power saving compared to an EL element using a conventional EL phosphor in its light emitting layer.

The size of the equivalent projected circle diameter of the pores on the surface of the phosphor particles and the amount of the EL phosphor containing the pores mixed into the light-emitting layer are determined by the amount of oxide added in the step of mixing the oxide and performing heat treatment. It can be changed by the heat treatment temperature and the concentration (PH) of the acid aqueous solution after the heat treatment.

Figure 3 shows that EL devices were fabricated using EL phosphors with various amounts of EL phosphor mixed in with holes, and the voltage was applied to 150V.
, as shown in the relative initial brightness and relative brightness curve (A) when applying a 4KHz alternating current.

The lifespan becomes longer when the amount of EL phosphor containing holes exceeds 20%, and the brightness increases when the amount of EL phosphor containing holes exceeds 10%, as shown in curve (B). Brightness increases. Accordingly, from the life curve (A) and the brightness curve (B), the preferred amount of EL phosphor having voids is 20% or more.

Figure 4 shows that EL devices are fabricated by forming a phosphor layer containing about 20% of EL phosphor with holes and a phosphor layer using conventional EL phosphor, and applying various voltages at 4KHz.
It shows the relative brightness of the applied voltage under certain conditions.

Curve (C) shows the brightness dependence of an EL element using an EL phosphor with holes on the applied voltage, and Curve 1 (D) shows
3 shows the dependence of brightness on applied voltage of an EL element using a conventional EL phosphor. Between the two, when comparing the applied voltage at the same brightness, an EL element using an EL phosphor with holes has a power saving characteristic of more than 10% in terms of applied voltage6. Although the explanation has been made using an EL element using a fluorescent layer containing about 20% of EL phosphor with holes, it goes without saying that the power saving characteristics will be further improved if the content of EL phosphor with holes is further increased. stomach.

A specific example will be described below.

500g of zinc sulfide precipitate and copper sulfate (CuSO, -58,O
) Add deionized water to 1.18g, mix to form a slurry, and dry this at 150°C for 12 hours.Next, add 15g of sodium chloride (NaCQ) to 500g of this mixture.
g, magnesium chloride (MgCff, 6H,0)
15g, strontium chloride (SrCI2*・6Hz
15 g of O) were mixed and filled into a quartz crucible, and the crucible was covered with a lid and fired in air at 1150°C for 6 hours.

After firing, remove the fired product from the quartz crucible and soak with deionized water.
After washing twice and filtering, it is dried at 150°C for 12 hours. Next, 200 g of this dried product was placed in a rubber bag and pressurized for 3 minutes with a hydrostatic pressure of 1000 kg/cd using a rubber press device. At this time, care must be taken not to let water get into the rubber bag. Next, take out the pressure-treated phosphor from the rubber bag and add zinc oxide (ZnO) to 100g of the pressure-treated phosphor.
Mix 5g, put it in a quartz crucible, make 1M, and heat at 750℃.
Bake in air for 1 hour.

After firing, the fired product was taken out from the quartz crucible, dispersed in deionized water, and hydrochloric acid (HCffi) was added to adjust the pH of the aqueous solution to 1.5.
After stirring and washing for 30 minutes, wash with deionized water five times. After filtration and drying, a phosphor having pores as shown in FIG. 1 was obtained through a 300-mesh sieving process. This was then used as an EL phosphor. This EL phosphor has SE
From the results of the M photograph, it was found that EL phosphor having about 70% pores was mixed in. This EL phosphor was kneaded with cyanoethyl cellulose and placed in the light emitting layer of the EL device to a thickness of 1100 μ. As a result of applying an alternating current of 150 V and 4 KHz to such an EL element, compared to an EL element using a conventional EL phosphor, the initial brightness was 1.8 times higher, the brightness half-life period was 2.6 times higher, and the applied voltage was 40% higher. A product with improved power saving was obtained.

Note that similar results can be obtained by mixing the EL phosphor of the present invention with a conventional EL phosphor.

〔Effect of the invention〕

The EL phosphor of the present invention has high brightness and long life.

Moreover, an EL element with excellent power saving properties can be realized.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of the EL phosphor having holes according to the present invention, Fig. 2 is an explanatory diagram showing the definition of the projection circle equivalent diameter, and Fig. 3 is a schematic diagram showing an example of the EL phosphor having holes of the present invention. FIG. 4 is a graph showing the relationship between the amount mixed into a layer, relative initial brightness, and relative brightness half-life period, and FIG. 4 is a graph showing the relationship between brightness and applied voltage of the EL phosphor of the present invention and the conventional EL phosphor. ,
FIG. 5 is a longitudinal sectional view showing a part of the structure of the organic dispersion type EL element. ■...Phosphor particle ■...Vacancy■...Projected circle equivalent diameter (14)...Light emitting layer (A)...Life curve (B)...Brightness curve Agent Patent attorney Rules near
Ken Yudo Kikuo Takehana Figure 1 Figure 2 Customer'F"3Lr"eSelect El-ba':l≧Se≧E 1
1 (ugh) mark 7ro angle (Y)

Claims (2)

[Claims] (1) 0.1 on the surface of phosphor particles whose matrix is zinc sulfide
An electroluminescent phosphor characterized by having pores having a projection circle equivalent diameter of ~2.0 μm. (2) The electroluminescent phosphor according to claim 1 is used as a light emitting layer,
An electroluminescent device characterized in that the electroluminescent phosphor is mixed in an amount of 20% or more based on the entire phosphor forming the light emitting layer.