JPS5913838B2 - Method for manufacturing electroluminescent material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a distributed electroluminescent material that exhibits luminescent properties upon application of a DC voltage.

■1■ Compound luminescent material ZnS, CdS, etc. are known as good electroluminescent materials, but in order to obtain light emission by applying a DC voltage to this type of luminescent material, it is necessary to pass a current through the luminescent layer. need to pass. For this purpose, it is necessary to apply Ib on the surface of the phosphor powder, which is usually activated with manganese or the like.
A conductive layer made of a group compound is formed. As specific methods for forming a conductive layer, direct vapor deposition of copper or immersion in a copper salt solution (Japanese Patent Publication No. 48-440710, Japanese Patent Publication No. 50-21080) have been known. 5 The conductive luminescent powder thus obtained is mixed with a suitable binder, coated uniformly on conductive glass, and a back electrode is attached to it to create an electroluminescent cell (hereinafter referred to as EL cell). do.

It is known that when a DC voltage is applied to this EL cell, it emits light with considerable brightness10. Such a DC type EL
A feature of the cell is that it exhibits a forming phenomenon (a phenomenon in which instantaneous current increases when voltage is applied) when voltage is applied.

For example, in the case of zinc sulfide, manganese, and copper-based DC electroluminescent materials, the brightness of the luminescent material increases with the amount of copper coating up to a certain limit of 15%, but on the other hand, as the amount of copper coating increases, the forming current also increases, and the Joule heating As a result, the EL cell is heated and the light emitting layer may peel off from the electrode or the conductive glass electrode may break. Therefore, while maintaining excellent brightness, forming current is suppressed,
It would be of great practical benefit if it were possible to prevent overheating of the EL cell due to the forming current. The present invention is an activated ■
-■ In a method for producing an electroluminescent material in which a conductive layer made of a group Ib compound is formed on the surface of a compound phosphor, after the conductive layer is formed, secondary firing is performed in an inert gas or vacuum. The present invention relates to a method for manufacturing an electroluminescent body characterized by the following.

30 The present invention is based on the discovery that when phosphor particles with a high amount of copper coating are subjected to secondary firing under specific conditions, the forming current decreases, and at the same time, the luminance increases significantly. .

That is, a conductive layer with a high copper content is formed on the surface of the zinc sulfide phosphor particles activated by manganese or the like through primary firing, using a copper salt dipping method, etc., and then ZnS:Mn, ZnS:Mn, When Cu particles are fired under specific conditions, the maximum current during forming can be significantly reduced, and at the same time, the luminance can be increased.

The purpose of the present invention is to reduce the forming current when the content of group Ib compounds in the conductive layer on the surface of an activated single compound is high, but the forming current is also noticeable when the content of group Ib compounds is low. Show effectiveness.

In other words, according to conventional knowledge, when the copper content is low in a ZnS:Mn,Cu luminescent material produced by copper vapor deposition or copper salt immersion method, almost no forming current is observed, and the light emission is non-uniform. Brightness is also low. However, when such phosphor particles with a low copper content are fired again under specific conditions described below, the light emission becomes uniform and the brightness is greatly improved. At this time, a slight forming current is observed as the luminance improves, but the maximum current remains at a small value. In this way, the present invention reduces forming current,
It has a remarkable effect on improving the luminance of the light emitter and improving the uniformity of light emission. The firing temperature during the second firing at which the effects of the present invention are manifested varies depending on the characteristics of the luminescent particles (particularly the content of Group Ib compounds), but the temperature range is from 300°C to 8°C.
00°C, preferably 400°C to 700°C. 300
If the temperature is lower than 800°C, the effects of the present invention will not be exhibited regardless of the firing time, and if the temperature is higher than 800°C, the crystals of the - compound will become coarse and the light emitting function will be significantly reduced.

On the other hand, the firing time depends on the firing temperature.

When the firing temperature is T (°C) and the firing time is t (minutes), the firing time t for achieving the effects of the present invention is calculated by the following formula:
-2.00×10-3XT+1.60<. TOgtku1
．． 48X10-3T+3.20, but 300℃ and T80
It is necessary to be determined by 0°C.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

Example 1 The amount of manganese as an activator with respect to zinc sulfide powder was 0.
Manganese acetate was added to the zinc sulfide slurry so as to have a weight of 3% by weight, and then water was removed and dried, followed by primary firing at 950° C. in a nitrogen gas stream for 1 hour to activate the zinc sulfide.

70% cuprous chloride of 0.046f dissolved in a small amount of hydrochloric acid
℃ deionized water 150cc. The phosphor ZnS:MnlOr was added to the solution while stirring vigorously, and the solution was stirred for 5 minutes, washed with water, and dried in vacuum.

The thermometer reading at this time was 150°C. Obtained ZnS
: Add polystyrene resin as a binder to Mn and Cu at a weight ratio of 7:3, adjust the viscosity with xylene, apply uniformly to conductive glass soil, and then dry thoroughly in vacuum to form an EL film with a film thickness of 40μ. A cell was produced and designated as EL cell (1).

Next, the ZnS:Mn,Cu phosphor obtained by the above method was fired at 600° C. for 20 minutes in a nitrogen stream. As a result of this second firing, the color tone of the ZnS:Mn,Cu particles changed from pale green to brownish brown. Polystyrene resin was added to the second fired luminescent particles at a weight ratio of 7:3, and an EL cell with a film thickness of 40 μm was prepared in the same manner as above.
This was designated as an EL cell (). When a DC voltage of 100 V was applied to each of the EL cells (1) and () thus obtained, the EL cell (1) showed almost no forming phenomenon, and the state of light emission was uneven and weak. .

On the other hand, the maximum forming current of the EL cell () is 1
The light emission remained at 5 mA/.d, and the light emission was uniform, and the light emission brightness was also greatly improved.

The emitted light color was yellow/orange and did not change before and after the second firing.

Example 2 ZnS:Mn was activated in the same manner as in Example 1, and 150 cc. ZnS:MnlOf was added to the solution, and after being immersed for 5 minutes, it was filtered, washed with water, and dried.

An EL cell ( ) having a film thickness of 40 μm was fabricated from the thus obtained ZnS:Mn, Cu in the same manner as in Example 1. Next, the above ZnS:Mn,Cu was fired at 500° C. for 20 minutes in a nitrogen stream.

An EL cell ( ) with a film thickness of 40 μm was produced from the second fired ZnS:Mn, Cu in the same manner as in Example 1.

When a DC voltage of 100 was applied to each of EL () and (), the maximum forming current of EL cell () was 300 m
A/i or higher was recorded, and a portion of the glass electrode was found to be broken.

On the other hand, in the EL cell (), it was 40 mA/word.
Furthermore, the relative luminance of the EL cell () was improved by about 20% compared to the EL (). Furthermore, the emitted light color is yellow/
The color was orange and did not change before and after the second firing.

Claims (1)

[Claims] 1. Production of an electroluminescent material in which a conductive layer made of a group Ib compound is formed on the surface of a II-VI compound phosphor activated by an activator by firing and bonded with a binder. A method for producing an electroluminescent material, which comprises forming the conductive layer and then performing a second firing in an inert gas or vacuum under conditions determined by the following formula. -2.00×10^-^3×T+1.60≦logt≦
-1.48×10^-^3T+3.20 However, 300℃≦
T≦800℃ where T is firing temperature (℃) t is firing time (minutes)