JPS62123692A - Reflective field light emiiting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electroluminescent device that emits light by applying an electric field to a phosphor layer, and particularly relates to an electroluminescent device that emits light by applying an electric field to a phosphor layer. The present invention relates to a reflection type electroluminescent device which reflects external light or light emitted from a phosphor layer by a counter electrode and emits it from a transparent electrode side.

[Prior Art] Conventionally, the luminescence phenomenon that occurs when an electric field is applied to a phosphor such as zinc sulfide in which copper or manganese is diffused is known as left luminescence (hereinafter abbreviated as EL).
Used in electroluminescent devices.

A conventional electroluminescent device using EL will be explained with reference to FIG. 1 is a transparent insulating substrate made of glass, plastic film, or the like.

2 is a transparent electrode formed inside the transparent insulating substrate 1, and is made of a thin film of metal oxide such as indium oxide or tin oxide, a thin film of gold, palladium, etc., or a thin film of aluminum, copper, etc. with small mesh holes formed therein. The layer is made of a thin film for entertainment and has a sheet resistance of 0.07 or less. 7 is a counter electrode provided facing the transparent electrode, and is made of, for example, metal powder such as silver dispersed in an organic polymer or inorganic binder, or metal foil or metal thin film of aluminum, copper, etc. Consisting of 3 is a phosphor layer provided between the transparent electrode 2 and the counter electrode 7, which is made by doping zinc sulfide with an activator such as copper or manganese and an activator such as aluminum or chlorine to form a phosphor powder. This is a layer made by dispersing silica in an organic polymer or inorganic binder. The phosphor powder used for the phosphor layer 3 is generally heated at 800°C to 120°C by adding a zinc sulfide activator and an activator.
It is produced by firing in an atmosphere of nitrogen, hydrogen sulfide, etc. at 0° C. to grow zinc sulfide particles. In addition to zinc sulfide, phosphor powders include those using rare earth elements, divalent metals, transition metals, and the like. 6 is an insulating layer similarly provided between the transparent electrode 2 and the counter electrode 7,
It is made by dispersing high dielectric constant powder such as titanium oxide or barium ditanate in an organic polymer binder. These layers are entirely covered with a moisture-proof protective film 5 made of trifluorochloroethylene, epoxy resin, or the like. When an alternating current voltage is applied between the transparent electrode 2 and the counter electrode 7, an electric field corresponding to the voltage and frequency is applied to the phosphor layer 3, causing it to emit light. Furthermore, in order to keep the humidity inside the moisture-proof protective film 5 low, a water-trapping film made of a hygroscopic film such as nylon 6 or nylon 6.6 or an inorganic desiccant agent such as zeolite, silica gel, or calcium oxide is used. Layered electroluminescent devices have also been used.

A structure in which a transparent electrode 2 and a transparent insulating substrate 1 are arranged at each position of 6.7 in FIG. 3, or a structure in which 1, 2.3 and 6 shown in FIG. Double-sided light-emitting electroluminescent devices are also known.

[Problems to be Solved by the Invention] However, the phosphor powders used in conventional electroluminescent devices have an average particle size of 20 to 30 μm, and some of them have a particle size of 35 μm or more. It also contains many large particles. For this reason, the thickness of the phosphor layer 3 and the insulating layer 6 shown in FIG. 1 is generally 40 μm to 60 μm. However, as the film thickness increases, the electric field applied to the phosphor powder becomes weaker, and the luminance of the emitted light also becomes lower. Therefore, the ratio of the phosphor powder in the phosphor layer 3 is increased (approximately 80% or more) to maintain the luminance at a practical level. Furthermore, as shown in FIG. 4, the surface of the phosphor powder has many irregularities, making it easy to scatter light. Therefore, the light transmittance of the phosphor powder itself is low. For the above reasons, the light transmittance of the phosphor layer 3 is extremely low (10
% or less. Therefore, the insulating layer 6 in FIG. 3 is omitted, the phosphor layer 3 is sandwiched between the transparent electrode 2 and the counter electrode 7, and the external light and the light emitted from the phosphor layer are reflected by the counter electrode and emitted from the transparent electrode 2 side. In a reflective electroluminescent device, when such a conventional phosphor powder is used for the phosphor layer 3, the amount of reflected light is extremely small because the transmittance of the phosphor layer 3 is low, so the reflective type is used. It is ineffective and cannot be put to practical use.

Therefore, such a reflective electroluminescent device has not yet been put into practical use, and has a structure as shown in FIG. 3 in which an insulating layer 6 is inserted to increase the electric field applied to the phosphor layer 3. Electroluminescent devices were common.

[Problems to be Solved by the Invention] Therefore, the present invention is essential by putting a reflective electroluminescent device into practical use, which has not been possible with conventional techniques, and in particular, by increasing the transmittance of the phosphor layer. Another object of the present invention is to provide a high-brightness reflective electroluminescent element having a structure in which external light or light emitted from a phosphor layer is reflected by a counter electrode and emitted from a transparent electrode side.

[Means for Solving the Problems] The present invention provides an electroluminescent element in which a phosphor layer is provided between a transparent electrode and a counter electrode, in which the phosphor layer has a thickness of 20 μm.
A reflective type comprising a phosphor powder having a particle size of m or less and a smooth crystal face, and characterized in that external light or light emitted from the phosphor layer is reflected by the counter electrode and emitted from the transparent electrode side. It is an electroluminescent device.

The reflective electroluminescent device according to the present invention has a phosphor layer in which phosphor powder is dispersed in an organic polymer binder between a transparent electrode formed on a transparent insulating substrate and a counter electrode that serves as a light reflecting plate. The conventional insulating layer is not provided.

The phosphor powder used in the phosphor layer of the present invention is a small particle size powder of 20 μm or less with a smooth surface, which has a two-step firing method to promote the growth of crystal planes. The electroluminescent device was made possible by obtaining a small-particle phosphor powder having a smooth surface on which such crystal planes have grown.

[Example] A preferred embodiment of the present invention will be described in more detail with reference to FIGS. 1 and 2.

The phosphor powder of the present invention is produced by pre-calcining zinc sulfide powder to which an activator and an activator have been added in an atmosphere of inert gas or hydrogen sulfide at 300°C to 600°C, and then
It is obtained by a two-step firing method including main firing at 1200°C. By doing so, a phosphor powder with sufficiently grown crystal planes and a smooth surface can be obtained. Preliminary firing is performed for 5 to 24 hours, preferably 10 to 15 hours, and main firing is performed for less than 10 hours, preferably 1 to 5 hours. Pre-firing and main firing are
It can be carried out continuously or separately, that is, after preliminary firing, it can be cooled once and fired again (main firing). Similar effects can be obtained in either case. This effect is basically not affected by the type or amount of the activator or activator. Figure 2 is an electron micrograph of zinc sulfide phosphor powder doped with copper and chlorine obtained by pre-firing at 500°C for 12 hours in a nitrogen atmosphere and then main firing at 900°C for 4 hours. be. As is clear from a comparison between FIG. 2 and FIG. 4, the phosphor powder of the present invention shown in FIG. 2 has a smooth surface and a small particle size. Furthermore, the transmittance of the phosphor powder itself has also increased. After firing, the phosphor powder was subjected to steps such as washing and classification, and only phosphor powder with a particle size of 20 μm or less was used in the reflective electroluminescent device described below. Fluorine rubber having a dielectric constant of 15 was used as the organic polymer binder.

FIG. 1 is a side sectional view of a reflective electroluminescent device according to the present invention, which was produced as follows.

Note that in order to make it a reflective type, the insulator layer 6 shown in FIG.
is not formed.

A transparent electrode 2 is formed on one side of a transparent insulating substrate 1 by a conventionally known appropriate means such as vapor deposition or coating. 60% phosphor powder in fluorine rubber was placed on transparent electrode 2 (Example 1)
), 40% (Example 2), a mixed paste was applied and dried to form a phosphor layer 3 (thickness: 20-20%).
5 μm). Next, a counter electrode 4 made of aluminum foil with metallic luster is bonded to the phosphor layer 3 by thermocompression bonding. Thereafter, terminals for voltage application are wired, and the entire structure is covered with a moisture-proof protective film 5 to form a reflective electroluminescent element.

[Conventional Example] The structure of the conventional electroluminescent device shown in FIG.
Using the phosphor powder shown in the figure, the ratio in phosphor layer 3 is 80.
%, and the thickness of the phosphor layer 3 and the insulator layer 6 is 35 to 40%.
A comparative amount was prepared in μm.

The transmittance and luminance (relative values) of the phosphor layer 3 of Examples 1 and 2 and the conventional example are shown in the following table.

In the embodiment, aluminum foil was used as the counter electrode 4 having a reflective structure, but other materials may also be used. For example, metal foils or thin films of gold, aluminum, copper, etc., or thin films of these metals may be used. Similar results can be obtained with the formed insulating substrate.

[Effects of the Invention] As explained above, according to the present invention, the use of a small-sized phosphor with a smooth surface in the phosphor layer, and the reflection by the counter electrode, make it more effective than conventional electroluminescent devices. □As a result, the thickness of the phosphor layer can be reduced, and the transmittance and luminance are significantly increased. . □34 Eh. 3 Ka1. Yo. . 438
When arranged as a backlight as shown in Fig. 6, outside light during the day enters through the liquid crystal display element and the phosphor layer 3, is reflected by the counter electrode 4 having a reflective structure, and then the light goes out of the liquid crystal display element. The light was emitted and the liquid crystal display was fully visible.

In fact, the reflective electroluminescent device of the present invention can be used not only as a backlight but also as a reflector for a liquid crystal display device.

In this way, the reflective electroluminescent device of the present invention has 1, transmittance,
This not only increases the luminance of light emission but also expands the uses of electroluminescent devices, and its practical value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a reflective electroluminescent device showing a preferred embodiment of the present invention, and FIG. 2 is an electron micrograph of the phosphor powder used in the reflective electroluminescent material of the present invention. 3 is a side sectional view showing the structure of a conventional electroluminescent device, and FIG. 4 is an electron micrograph of phosphor powder used in the conventional electroluminescent device. 119. Transparent insulating substrate, 2.1. Transparent electrode, 391. Phosphor layer, counter electrode with 4111 reflection structure, 53. , moisture-proof protective film, 681. Insulator layer, 711
．． Counter electrode, Figure 1 O 2 Mouth 3 Figure 74 Figure procedure amendment (JRI February 12, 1986)

Claims (1)

[Claims] In an electroluminescent device in which a phosphor layer is provided between a transparent electrode and a counter electrode, the phosphor layer contains a phosphor powder having a particle size of 20 μm or less and a smooth crystal face,
A reflective electroluminescent device characterized in that external light or light emitted from the phosphor layer is reflected by the counter electrode and emitted from the transparent electrode side.