JPH02223191A - Electroluminescent device - Google Patents

Abstract

PURPOSE:To obtain an electroluminescent device with low electricity consumption by suppressing polarization of an interface between a fluorescent layer and a dielectric layer which form a luminescent layer by matching dielectric constant and conductivity of these layers. CONSTITUTION:A luminescent layer 3 is comprised of a fluorescent layer 4 in a transparent electrode 1 side and a dielectric layer 5 in the opposite electrode 2 side and the luminescent 3 is so made to emit light by application of an electric field of an alternating current between the transparent electrode 1 and the opposite electrode 2. Electric properties of the fluorescent layer 4 and the dielectric layer 5 are matched each other by mixing a transparent dielectric powder in the former layer or mixing conductive powder in the dielectric layer 5, and both layer are thus made to seemingly be uniform dielectrics so as to decrease polarization of the interface between both layers. By this method, an electroluminescent device with low electricity consumption is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention involves interposing a light-emitting layer between a transparent electrode and a counter electrode, and forming an electric field by applying an electric field between the transparent electrode and the counter electrode. The present invention relates to an electroluminescent element in which a light-emitting layer emits light.

[Conventional technology]

Electroluminescent elements are widely used as backlights in display devices of various devices, display elements themselves, and the like. This electroluminescent element has a light-emitting layer interposed between a transparent electrode and a counter electrode, and generates light by forming an alternating current electric field between the two electrodes.The light-emitting layer includes: Consists of a phosphor layer made by dispersing phosphor powder in a binder resin, and a dielectric layer formed by mixing a high dielectric constant resin material or a high dielectric fine powder such as ceramic powder into it. It is now possible to do so.

[Problem to be solved by the invention]

By the way, in the conventional electroluminescent device described above, the phosphor layer and the dielectric layer that constitute the light emitting layer are inhomogeneous dielectric materials with different dielectric constants and conductivities, so that the phosphor layer and the dielectric layer that constitute the light emitting layer are inhomogeneous dielectric materials that have different dielectric constants and conductivities. There is a problem in that a polarization phenomenon called interfacial polarization occurs at the interface between the body layer and the dielectric layer, and this interfacial polarization increases power consumption. For this reason, such electroluminescent elements are unsuitable for backlighting, for example, battery-powered laptop computers, and there is still room for improvement.

Therefore, an object of the present invention is to provide an electroluminescent element with low power consumption in view of the actual state of the prior art described above.

[Means to solve the problem]

In order to achieve the above object, the present invention interposes a light-emitting layer consisting of a phosphor layer and a dielectric layer between a counter electrode and a transparent electrode, and provides an alternating current between the counter electrode and the transparent electrode. In an electroluminescent device that causes the phosphor layer to emit light by applying an electric field, transparent dielectric powder is mixed in the phosphor layer, or conductive powder is mixed in the dielectric layer, and the phosphor layer is made to emit light. The feature is that the electrical properties of the body layer and dielectric layer are matched.

[Effect]

By matching the electrical properties of the phosphor layer and the dielectric layer as described above, both layers become pseudo-homogeneous dielectrics and the interfacial polarization is reduced.

[Example Go Hereinafter, embodiments of the present invention will be described based on the drawings.

The figure is a cross-sectional view of an electroluminescent device according to an embodiment of the present invention. In the figure, 1 indicates a transparent electrode, and 2 indicates a counter electrode. Between the transparent electrode 1 and the counter electrode 2, there is a light-emitting layer. 3 is interposed. This luminescent layer 3 is composed of a laminate of a phosphor layer 4 on the transparent electrode 1 side and a dielectric layer 5 on the counter electrode 2 side, and emits light by applying an alternating current electric field between the transparent electrode 1 and the counter electrode 2. Layer 3 is adapted to emit light.

Here, the compositions of the phosphor layer 4 and the dielectric layer 5 are different from the usual compositions already explained as conventional examples, and by making one or both of them have the following composition, the electrical characteristics of each other can be approximated. It is designed to be equal to That is, for the phosphor layer 4, the dielectric constant of the phosphor layer 4 is increased by mixing a transparent dielectric powder with a high dielectric constant into a normal composition in which phosphor powder is dispersed in a binder resin. The dielectric constant of layer 4 is brought close to that of dielectric layer 5. On the other hand, dielectric layer 5
For this purpose, the conductivity can be increased by mixing conductive powder such as silver, nickel, or phosphor into the usual composition of high dielectric constant resin material or high dielectric constant ceramic dielectric powder mixed therein. The conductivity of the dielectric layer 5 is brought close to that of the phosphor layer 4. The interfacial polarization that occurs at the interface between the phosphor layer 4 and the dielectric layer 5 can be minimized when both layers have the same dielectric constant and conductivity. Even if only one side is matched, it can be significantly reduced.

The electroluminescent device according to this example is constructed as described above, and the manufacturing process thereof will be illustrated next.

<Specific Example 1> First, a phosphor layer 4 having a known composition is formed on a transparent electrode 1 by coating. Here, the phosphor layer 4 is made of, for example, zinc sulfide with a small amount of copper added as a phosphor powder, cyanoethyl cellulose and cyanoethyl saccharose as a binder resin, and N,N-dimethylformamide (DMF) as a solvent. in weight ratio of phosphor powder 8. Cyanoethyl cellulose 1. Cyanoethyl sucrose 1. A paste mixed with DMF in a proportion of 7 is applied onto the transparent electrode 1 to form a fluorescent layer 4 having a thickness of about 40 μm after drying.

Next, as the dielectric layer 5, a known dielectric paste mixed with conductive powder is used, and this is coated and dried on the phosphor layer 4 to form a film with a thickness of about 40 μm. A dielectric layer 5 is formed. Here, as the dielectric layer 5, for example, cyanoethyl sucrose to 1 part cyanethyl cellulose is 1 part. Titanium oxide powder 1. DMF7. Using a dielectric paste mixed at a ratio (weight ratio) of 1 part phosphor powder,
By adjusting the amount of the phosphor powder used as the conductive powder, the respective conductivities of the lower phosphor layer 4 and the upper dielectric layer N5 are matched.

Furthermore, a silver paste as a counter electrode 2 is applied onto the dielectric layer 5 and dried to obtain an electroluminescent element as shown in the figure.

Separately from the electroluminescent device of Example 1 thus obtained, a dielectric layer of 1 part cyanethyl cellulose and 1 part cyanoethyl saccharose was used. Titanium oxide powder 2. An electroluminescent device was formed using a dielectric paste mixed with DMF at a ratio (weight ratio) of 7. The phosphor layer was the same as in Example 1). An alternating current electric field was applied, and the voltage (V) and current (A) were measured when the brightness reached 50 cd/% to determine the apparent power (■·A).

Table 1 From the measurement results in Table 1, it can be seen that according to the electroluminescent element of Specific Example 1 in which phosphor powder was mixed in the dielectric layer 5, the comparative example in which phosphor powder was not mixed in the dielectric layer 5 was Conventional example)
It has been revealed that the apparent power is reduced by about 30% compared to the electroluminescent element shown in FIG.

In Example 1, other conductive powders such as silver powder or nickel powder may be used instead of the fluorescent powder mixed in the dielectric layer 5, but in particular, the fluorescent powder in the fluorescent layer 4 When the same phosphor powder as the phosphor powder is mixed into the dielectric layer 5, matching of the conductivities of both layers 4 and 5 becomes easy. In addition, when the amount of conductive powder mixed into the dielectric layer 5 increases,
It is necessary to apply an insulating coating to the surface of the conductive powder so that the conductive powder does not short-circuit within the dielectric layer.

<Specific Example 2> First, on the transparent electrode 1, a known phosphor paste mixed with a transparent, high-permittivity dielectric powder is prepared, for example, cyanoethyl cellulose to 1 part cyanoethyl saccharose. Fluorescent powder6. DMF7. A phosphor paste mixed with PLZT powder (average particle size 1 μm or less) at a ratio (weight ratio) of 2 parts is applied and dried to a film thickness of about 40 μm.
A phosphor layer 4 is formed. Here, by adjusting the amount of the PLZT powder used as the dielectric powder, the dielectric constants of the phosphor layer 4 and the dielectric layer 5 formed thereon, which will be described later, are matched.

Next, a known dielectric paste, for example the same dielectric paste used in the above-mentioned comparative example, is applied onto this phosphor layer 4, and this is dried to form a dielectric paste with a thickness of approximately 40 μm. Form layer 5. Thereafter, a silver paste is applied as a counter electrode 2 onto the dielectric layer 5, and this is dried to obtain an electroluminescent element as shown in the figure.

Regarding the electroluminescent element of Specific Example 2 obtained in this way, the apparent power was determined using the same measurement method as in Specific Example 1, and the apparent power was 0.0094 V.
-A/a (This result shows that Example 2 can also provide an electroluminescent element with low power consumption.

In addition, in each of the above-mentioned specific examples 1.2, the conductivity or permittivity of either the phosphor layer 4 or the dielectric layer 5 constituting the light emitting layer 3 is different from the conductivity or permittivity of the other. The case has been described in which the interfacial polarization of both layers 4 and 5 is reduced by matching them, but by combining these specific examples 1 and 2, the mutual conductivity and permittivity of the phosphor layer 4 and dielectric layer 5 can be reduced. It is also possible to match. In this case, although the manufacturing process becomes somewhat complicated, almost no interfacial polarization occurs between the two layers 4 and 5, and the power consumption of the negative layer can be reduced.

〔Effect of the invention〕

As explained above, the present invention matches the dielectric constant and conductivity of the phosphor layer and dielectric layer that constitute the light emitting layer,
Since it is designed to suppress the interfacial polarization between the two layers,
An electroluminescent element with low power consumption can be provided.

[Brief explanation of the drawing]

The figure is a sectional view of an electroluminescent device according to an embodiment of the present invention. 1...Transparent electrode, 2...Counter electrode, 3
...Light emitting layer, 4...Fluorescent layer, 5...
...Dielectric layer. Transparent electrode pair Electroluminescent layer Fluorescent layer Dielectric V body eyebrow

Claims (3)

[Claims] (1) By interposing a light emitting layer consisting of a phosphor layer and a dielectric layer between a counter electrode and a transparent electrode, and applying an alternating current electric field between the counter electrode and the transparent electrode, An electroluminescent device in which the phosphor layer emits light, characterized in that the phosphor layer contains transparent dielectric powder. (2) By interposing a light emitting layer consisting of a phosphor layer and a dielectric layer between the counter electrode and the transparent electrode, and applying an alternating current electric field between the counter electrode and the transparent electrode, An electroluminescent element in which the phosphor layer emits light, characterized in that the dielectric layer contains conductive powder. (3) The electroluminescent element according to claim (2), characterized in that the surface of the conductive powder is coated with an insulating film.