JP2593522B2 - Electroluminescent phosphor and electroluminescent device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an organic dispersion type electroluminescent phosphor and an electroluminescent element.

(Prior art) Electroluminescence (hereinafter referred to as EL) is a light emission phenomenon that occurs when a high electric field is applied to a phosphor substance. Dispersion type EL is roughly divided into enamel type (or inorganic type) and plastic type. (Or organic type).

Compared with the former method, in which the EL phosphor is mixed with a glass fritter and baked on an iron plate, the latter method, in which the EL phosphor is dispersed in a binder having a high dielectric constant to form a light emitting layer, is thinner and lighter. Recently, the latter has been awarded because it can realize an arbitrary shape and obtain high luminance.

FIG. 4 shows a partial cross-sectional view of the basic structure of the organic dispersion type EL element. As can be seen from the figure, the EL element has an insulating layer (13)
And a light emitting layer (14) composed of a back electrode layer (12) made of aluminum foil and a transparent electrode layer (15) made of at least one of In ₂ O ₃ , SnO ₂ and a mixed system of In ₂ O ₃ -SnO _2. An electrode lead wire (18) extending to the outside of the EL element is connected to a part of the back electrode layer made of aluminum foil, sandwiched from above and below, and between the other transparent electrode layer and the light emitting layer. EL
An extraction electrode lead wire (19) to the outside of the element is connected. Furthermore, the whole is covered with protective films (11) and (16),
The structure prevents moisture from the outside.

The EL device having the above-described structure can provide the above-described thin and light emitting device of any shape, but is considerably inferior in brightness and life characteristics as compared with other display devices, so that its application range is limited. Under such circumstances, various improvements have been made conventionally.

For example, among the EL device constructions, cyanoethyl cellulose (Japanese Patent Publication No. 38-8258), cyanoethyl sucrose, cyanoethyl pullulan, cyanoethyl vinyl, and vinylidene fluoride (Japanese Utility Model Laid-Open No. 49-125668) as an improvement of a high dielectric constant organic binder. ) Etc. are known. Further, there is known a method of mixing barium titanate powder to increase the dielectric constant (Japanese Patent Laid-Open No. 60-216498).

The EL phosphor used in the light emitting layer is used as a base material.
It is a well-known fact that II-VI compounds such as ZnS are mainly used, and various luminescent colors can be obtained by adding atoms such as copper, manganese, chlorine, and bromine as an inactivator or coactivator. is there. This ZnS is changed easily due to moisture absorption due to moisture during the operation of the EL element and becomes a dark point, so it is likely to deteriorate, so a moisture absorption layer is made of nylon etc. so that moisture does not reach the light emitting layer.
There is also disclosed a method for preventing the deterioration of the resin (JP-A-60-250592).

However, the introduction of nylon or the like for improving the high dielectric constant organic binder and for preventing deterioration due to moisture is a secondary factor from the viewpoint of improving the characteristics (brightness and life characteristics) of the EL element. The improvement in the characteristics of the device is largely affected by the EL luminous body used in the luminous layer. Therefore, as a conventional improvement of the EL phosphor, the particle diameter of the phosphor has been reduced by approximately
It is known to increase it to 20-30 μm. However, an EL element using a phosphor having such a large particle diameter has a high applied voltage at the time of driving, the phosphor is quickly deteriorated, and does not necessarily have a long life.

On the other hand, a proposal by the same applicant as the present application (Japanese Unexamined Patent Publication No.
No. 6085), a method for obtaining a long-lifetime phosphor by producing a large-particle-size hexagonal-type intermediate phosphor and applying high-pressure to a large-particle-size cubic-type phosphor. 61−188484
JP-A No. 10-205,086 discloses a method for extending the life by adding a small amount of a barium compound before firing, and optimizing the addition amount of copper as an activator and bromine as a coactivator to obtain a long-life phosphor ( JP-A-57-
No. 145174) A method has been proposed.

(Problems to be Solved by the Invention) In view of the above circumstances, the present invention significantly reduces the applied voltage at the time of driving by using a high-luminance, long-life EL phosphor and the EL phosphor in a light-emitting layer of an EL element. High power saving
An object is to provide an EL element.

[Configuration of the invention]

(Means and Actions for Solving the Problems) The present inventors have studied various methods of processing a phosphor in order to achieve the above objects. As a result, the phosphor and ZnO,
After mixing oxides such as Sb ₂ O ₃ , SnO ₂ , and PbO and performing a heat treatment at 600 to 900 ° C., and washing with an acid such as a mineral acid, pores are formed on the surface of the EL phosphor particles. As the specific surface area increases, the efficiency of EL luminance with respect to applied voltage is improved and EL
It has been found that a so-called long-life EL phosphor and EL element having a long half-life of luminance can be obtained.

That is, the present invention is an EL phosphor having pores having a projected circle equivalent diameter of 0.1 to 2.0 μm on the surface of phosphor particles having zinc sulfide as a base, and using this EL phosphor in a light emitting layer of an EL element. The phosphor is characterized in that the EL phosphor is mixed in 20% or more with respect to the whole phosphor forming the light emitting layer.

As shown in FIG. 2, the projected circle equivalent diameter is expressed on page 55 in the revised second edition of “powder” published by Maruzen Co., Ltd. on May 12, 1979. The diameter of the frontage of the pore is shown by referring to the definition of the particle diameter based on the projected image of the particle. The numerically limited projected circle equivalent diameter and the ratio of the phosphor having pores occupying the entire particle are measured based on a photograph taken of an average EL phosphor by an electron microscope (SEM). In the present invention, zinc sulfide is used as a base,
To this at least one of copper or manganese as an activator,
The co-activator contains at least one of chlorine, bromine, chromium and aluminum.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Copper compounds such as copper sulfate (copper concentration 0.02-0.2w)
t%) in the form of a slurry, followed by mixing and drying. Then, at least one of alkali metal, ammonia and halide of alkaline earth metal is added as a flux to the mixture in an amount of 3 to 10% by weight.
Mix. Thereafter, the mixture is filled in a quartz crucible, covered, baked in air at a temperature in the range of 1100 to 1200 ° C. for 3 to 10 hours, washed with deionized water several times, dried, and dried for intermediate fluorescence. Make a body. After heating and pressurizing treatment to the intermediate phosphor, pressure treated phosphor ZnO, Sb ₂ O _3, a SnO _2, oxide 10 or the like PbO mixed 3~10wt%. The mixture is then placed in a crucible, covered, and at a temperature in the range of
Heat treatment in air for hours. After heat treatment, acid solution such as hydrochloric acid, nitric acid, sulfuric acid, etc. is added and the washing process is performed in the range of PH1 ~ 5.
An EL phosphor is obtained.

The EL phosphor is dispersed in an organic binder having a high fusion rate, such as cyanoethylcellulose, together with a solvent to form a paste, and a dielectric such as barium titanate is coated on an aluminum foil serving as a back electrode layer (12) with a solvent. It is dispersed and applied as a paste, and is applied and dried to form an insulating layer (13), and then applied and dried to form a light emitting layer (14).
On the aluminum foil substrate thus obtained, take out the electrode lead wire (1) at the end of the aluminum foil opposite to the light emitting layer.
8) Fix. On the other hand, In ₂ O ₃ in an organic transparent film such as _{polyester, SnO 2, In 2 O 3} -SnO 2 comprising a mixed system Izure one or more conductive transparent electrode layer material was coated or vacuum deposited conductive side (15) Fix the extraction electrode lead wire (19) to the end. Thereafter, 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 laminated, and then the whole is covered with protective films (11) and (16) from both upper and lower surfaces. EL by pressure bonding
Obtain the element.

Such an EL element is an EL device using a conventional EL phosphor for a light emitting layer.
It has been found that the EL device has higher luminance, longer life, and higher power saving characteristics than the device.

The size of the projected circle equivalent diameter of the holes on the phosphor particle surface and the amount of the EL phosphor having the holes mixed into the light-emitting layer are determined by the amount of the oxide added in the step of heat-mixing the oxide. And the heat treatment temperature and the concentration (PH) of the acid aqueous solution after the heat treatment.

FIG. 3 shows EL phosphors in which the amount of mixed EL phosphors having vacancies was varied in various ways. EL devices were manufactured, and the relative initial luminance and relative luminance curve when an AC of 150 V, 4 KHz was applied thereto ( As shown in A), the lifetime becomes longer when the amount of the EL phosphor having pores exceeds 20%, and the luminance of the EL phosphor having pores increases as shown in the curve (B). Mixing amount
If it exceeds 10%, the brightness increases. Therefore, the life curve (A)
From the luminance curve (B), the mixing amount of the EL phosphor having a preferable hole is 20% or more.

Fig. 4 shows the formation of a phosphor layer containing approximately 20% of EL phosphor with holes and a phosphor layer using a conventional EL phosphor, and manufacturing EL devices, and applying various voltages to this at a constant 4KHz. It shows the relative luminance when applied under conditions.

Curve (C) shows the luminance dependence on the applied voltage of the EL element using the EL phosphor having holes, and curve (D) shows the luminance dependence on the applied voltage of the EL element using the conventional EL phosphor. Is shown. Comparing the applied voltage between the two at the same luminance, the EL element using the EL phosphor having holes has a power saving characteristic of 10% or more in terms of applied voltage.

In FIG. 4, an EL device using a phosphor layer containing about 20% of an EL phosphor having holes is described.
Needless to say, if the content of the phosphor is further increased, the power saving characteristics are further improved.

 Hereinafter, specific examples will be described.

Deionized water was added to the zinc sulfide precipitates 500g and copper sulfate _{(CuSO 3 · 5H 2 O)} 1.18g were mixed with a slurry, this 150
Dry at 12 ° C for 12 hours. Next, sodium chloride (NaCl) 15 g, magnesium chloride (MgCl ₂ .6H ₂ O) 1
5 g and 15 g of strontium chloride (SrCl ₂ .6H ₂ O) are mixed, filled in a quartz crucible, covered, and baked at 1150 ° C. for 6 hours in air.

After firing, the fired product is taken out of the quartz crucible, washed five times with deionized water, filtered, and dried at 150 ° C. for 12 hours.
Next, 200 g of the dried product was put in a rubber bag and pressed with a hydrostatic pressure of 1000 kg / cm ² for 3 minutes using a rubber press. At this time, care must be taken to prevent water from entering the rubber bag. Next, take out the pressed phosphor from the rubber bag, mix 5 g of zinc oxide (ZnO) with 100 g of the pressed phosphor, put it in a quartz crucible, cover and bake in air at 750 ° C for 1 hour . After firing, the fired product is taken out of the quartz crucible, dispersed in deionized water, added with hydrochloric acid (HCl) to maintain the pH of the aqueous solution at 1.5, washed with stirring for 30 minutes, and then washed five times with deionized water. After filtration and drying, a phosphor having pores as shown in FIG. 1 was obtained through a 300-mesh sieving process. This was used as an EL phosphor. According to the result of the SEM photograph, the EL phosphor having about 70% of the pores was mixed in this EL phosphor. This EL phosphor is kneaded with cyanoethylcellulose, and 100
It was arranged with a film thickness of μm. As a result of applying an alternating current of 150 V, 4 KHz to such an EL device, the initial luminance was increased 1.8 times, the luminance half-life was improved 2.6 times, and the power saving was reduced by 40% in terms of applied voltage, as compared with the EL device using the conventional EL phosphor. Things were obtained.

The same result can be obtained by mixing the EL phosphor of the present invention with a conventional EL phosphor.

〔The invention's effect〕

The EL phosphor of the present invention can realize an EL device having high luminance, long life, and excellent power saving.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of an EL phosphor having holes according to the present invention, FIG. 2 is an explanatory view showing the definition of a projected circle equivalent diameter,
FIG. 3 is a graph showing the relationship between the amount of the EL phosphor of the present invention mixed into the light-emitting layer and the relative initial luminance and the relative luminance half-life period. FIG. FIG. 5 is a graph showing the relationship between luminance and applied voltage in a graph. FIG. 5 is a longitudinal sectional view showing a part of the structure of an organic dispersion type EL element. (1) phosphor particles, (2) pores (3) equivalent projected circle diameter, (14) light emitting layer (A) lifetime curve, (B) luminance curve

Claims (2)

(57) [Claims] 1. The method according to claim 1, wherein the surface of the phosphor particles whose main body is zinc sulfide is 0.1 μm.
An electroluminescent phosphor having holes having a projected circle equivalent diameter of 1 to 2.0 μm. 2. The electroluminescent device according to claim 1, wherein the electroluminescent phosphor is a light emitting layer, and the electroluminescent phosphor is mixed in an amount of 20% or more with respect to the entire phosphor forming the light emitting layer. .