JPS5923437B2 - electroluminescence device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electroluminescence (hereinafter referred to as EL) device which is designed to improve luminance and extend life.

EL devices that utilize the light emission phenomenon that occurs when an electric field is applied to a phosphor have conventionally been developed by dispersing phosphor powder processed for EL in a dielectric material with a high dielectric constant, or by laminating it into a thick film. Two types of EL devices are known: a powder-type EL device that uses a phosphor, and a thin-film EL device that uses a phosphor thin film formed by vacuum deposition or the like.

There are also powder type and thin film type driving sources, one driven by an AC power source and the other driven by a DC power source. For example, as a powder-type EL device driven by a DC power source, one having a structure schematically shown in FIG. 1 is known.

That is, on a transparent substrate 1 made of glass or the like, sn
It has a structure in which a transparent electrode 2 such as O2 or N2O3 is deposited, a phosphor layer 3 made of a phosphor treated for EL is laminated thereon, and a back electrode 4 is deposited. .

Here, the phosphor layer 3 is treated in such a way that a certain amount of current flows through the phosphor layer 3 for direct current driving.

For example, when ZnS:Mn is used as a phosphor, the phosphor particles 5 are immersed in a solution of copper sulfate or copper acetate,
A phosphor in which a CuxS (1≦X≦2) layer 6 is formed on the surface of the phosphor particles 5 is used. However, in the EL device having the structure shown in FIG. 1, when a DC voltage is applied with the transparent electrode 2 side set to 1 and the back electrode 4 side set to θ, a so-called forming phenomenon occurs, causing the CuxS layer on the transparent electrode 2 side to Cu ions move into the interior of the phosphor particles 5 due to the electric field, and Cu ions are deposited in the part in contact with the transparent electrode 2.
It is believed that a high resistance portion without the xS layer 6 is formed and a high electric field is applied thereto, causing the phosphor layer 3 to emit light.

However, in the EL device having the structure shown in FIG.
In the portion of the phosphor layer 3 in contact with the transparent electrode 2,
As the diffusion of Cu ions into the phosphor particles 5 progresses, the carrier concentration in the phosphor particles 5 decreases, causing a phenomenon in which the current decreases and the luminance gradually decreases, resulting in an extremely short lifetime. There is.

Furthermore, the light emission operation is also unstable. On the other hand, in a thin film type EL device, the phosphorescent layer is extremely thin, about 10 μm at most, so that dielectric breakdown is less likely to occur in the light emitting layer due to pinholes or the like due to the high electric field applied to this portion.

Therefore, it is difficult to obtain sufficient brightness for display because the applied voltage cannot be high. In addition, as a solution to this problem, an EL device has been put into practical use that has a structure in which a dielectric layer is laminated on a thin film light emitting layer and is driven by an AC power source, but in this case, the driving voltage is 200V~ 400
The voltage is extremely high, on the order of V, making the drive circuit complicated and difficult to control.

Therefore, although this EL device is expected to be used as a surface light source or a medium to large-sized flat display device, to date it has only been applied in specific fields and has not yet been widely used as a display device. It's not working.

The present invention was made in view of the above-mentioned circumstances, and
On the upper surface of a transparent substrate, at least a transparent electrode, a first phosphor layer containing an activator, a conductive layer, and a phosphor powder are formed, and the surface of the phosphor powder is coated with a conductive film. The new structure of laminating the second phosphor layer, which has a low resistance, and the back electrode, improves the luminance of the light emitted from the EL device, and also greatly improves the lifespan of the EL device, especially when using a DC power source. The object is to provide a driven EL device.

Embodiments of the EL device according to the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view of essential parts showing an embodiment of the EL device according to the present invention.

Here, 11 is a substrate made of a transparent material such as glass, and a transparent electrode 12 made of 1N, 03 or SnO2 is deposited on this substrate 11 in a desired shape by vacuum evaporation, sputtering, spraying, or the like. do.

In addition, a - group compound such as ZnS, ZnSe, (ZnCd)S (ZnS will be explained as an example below) is used as a matrix, and transition elements such as Mn, b group elements such as Cu and Ay, and Eu A phosphor doped with rare earth elements such as The first phosphor layer is a thin film obtained by annealing at preferably 500'C to 600C so that the activator becomes a substituted atom.

In this case, the phosphor layer 13 may be formed by first forming a ZnS thin film that does not contain an activator by the above-mentioned means, and then doping it with an activator such as Mn during the annealing. .

Furthermore, when doping ZnS with an activator, a co-activator such as Al or C2 may be doped simultaneously with an element serving as an activator.

Further, the doping amount of the activator varies depending on the element, but M
In the case of n, the appropriate amount is about 0.1 to 3% by weight based on the ZnS matrix, and the thickness of the phosphor film 13 is 0.1 to 3 μm1.
Preferably, the thickness is about 0.5 to 1 μm. Reference numeral 14 denotes a conductive layer, such as a CuxS layer, deposited on the phosphor layer 13, and is formed by a vacuum evaporation method, a sputtering method, an ion blating method, etc. in the same manner as the formation of the phosphor layer 13. Alternatively, the substrate 11 on which the phosphor layer 13 has been formed may be immersed in a solution of copper sulfate, copper acetate, copper oxalate, etc. and heated at an appropriate temperature to form the phosphor layer 1.
It may be made to precipitate as CuxS on the surface of 3.

Furthermore, 15 is a second phosphor layer obtained by depositing phosphor powder on the conductive layer 14. This phosphor layer 1
Similarly to the phosphor layer 13, phosphor particles doped with an activator such as Mn or Cu and, if necessary, a co-activator such as Al or Cl, are coated with copper sulfate, copper acetate, By immersing the phosphor particles in a solution such as copper oxalate, heating the solution to 60 to 70°C, and stirring for about 0.5 to 2 hours, the surface of the phosphor particles 21 is coated as shown in FIG. A phosphor is used in which a CuxS layer 22 is deposited to form a conductive film.

However, the phosphor of the lever is mixed with an appropriate amount of a binder such as ethyl cellulose or acrylic acid resin dissolved in a solvent to form a paste, and then applied onto the conductive layer 14 by a method such as screen printing or coating. It is deposited to a thickness of about 5 to 100 μm.

Further, on this phosphor layer 15, a back electrode 16 made of Al or the like is deposited by vacuum evaporation or the like to form an EL device. However, in the configuration described above, the transparent electrode 1
If the DC power source 17 is connected so that the 2 side is 1 and the back electrode 16 side is 0, the phosphor layer 13 emits light.

That is, the phosphor layer 13 usually has high electrical resistance;
Further, the phosphor layer 15 has Cux on the surface of the phosphor particles.
It consists of a phosphor layer with a low resistance formed by a conductive film of S.

Therefore, most of the electric field generated by the DC power supply 17 is
The free electrons applied to the phosphor layer 13 and accelerated by this high electric field collide and excite the luminescent center of the phosphor layer 13, so that the phosphor layer 13 emits light. considered to be a thing.

Alternatively, the light emitting mechanism in this case can be considered as follows.

In general, ZnS:Mn phosphors are n-type semiconductors, whereas CuxS tends to be p-type semiconductors.

Therefore, a pn junction is formed at the junction surface between the phosphor layer 13 and the conductive layer 14, and by applying a very large reverse bias voltage to this pn junction, the conductive layer 1
It is also considered that electrons are injected from the 4 side to the phosphor layer 13 side, and these electrons are further accelerated by a high electric field and excite the luminescent center of the phosphor layer 13, causing light emission. Thus, the light emitted from the phosphor layer 13 is extracted in the direction of the arrow L through the transparent electrode 12 and the substrate 11 and is observed. In this case, as described above, a high electric field is applied by the DC power supply 17 between the transparent electrode 12, the phosphor layer 13, and the conductive layer 14, and when this high electric field is locally concentrated, it penetrates these layers. Pinholes occur due to dielectric breakdown.

However, the EL device according to the present invention has a structure in which a phosphor layer 15 made of phosphor powder whose surface is coated with a CuxS layer is laminated on the conductive layer 14. When a pinhole is generated due to a cause, the Cu ions on the surface of the phosphor powder particles above the pinhole are diffused into the phosphor particle, causing a forming phenomenon similar to that explained in FIG. It has a self-repairing function in which the phosphor particles in the hole portion emit light to restore the light-emitting function.

Note that when the second layer 15 made of phosphor powder is brought into direct contact with the thin film of the first phosphor layer 13 and the conductive layer 14 is omitted, the second layer 1. ! A part of the outer periphery of each powder particle forming the phosphor layer 13 comes into contact with the first phosphor layer 13, and the contact area becomes narrow and unstable, which in turn accelerates dielectric breakdown due to concentration of high electric field. This problem occurs. As a result, stable light emitting operation can be obtained, and it is also possible to apply a high electric field to the phosphor layer 13, thereby making it possible to significantly improve the luminance of light emission.

Furthermore, since there are no Cu ions on the first side of the phosphor layer 13 that emits light, there is no problem of reduction in luminance due to diffusion of Cu ions, and a significant improvement can be expected in terms of life. It is.

By the way, the structure shown in FIG. 2 described above shows the basic configuration of the present invention, and various other embodiments of the EL device of the present invention can be considered. For example, in the structure shown in FIG. 2 described above, a resin coating may be applied from above the back electrode 16 so as to seal each part thereof.

Alternatively, a lid may be provided to cover each part from the back electrode 16 side, and the inside thereof may be filled with dry gas, silicone oil, or the like. By doing so, the mechanical strength of the EL device itself can be improved, and it is also effective in protecting the EL device from moisture and other environmental conditions, resulting in a more reliable device. Further, the EL device according to the present invention can of course be used not only as a light source but also as various display devices.

For example, the transparent electrode 12 or the back electrode 1 shown in FIG.
It is also possible to construct a single-digit or multi-digit numerical display device by dividing at least one of the numbers 6 into diagonal shapes as shown in FIG.

Furthermore, if at least one of the transparent electrode 12 and the back electrode 16 is divided into linearly arranged dots, an analog display device with a so-called bar graph display can be obtained, as shown in FIG. 5X7 or 7X9
By dividing and arranging them in a dot matrix, it is possible to obtain a display device for characters or graphics, or a flat display device in place of a cathode ray tube. In this case, if an insulating layer with openings in each segment or dot is provided between the substrate and the back electrode, the optical separation of each light emitting part can be ensured, making it extremely easy to see, and also providing fluorescent light. Since the body layer and the back electrode can be easily supported, a sturdy display device can be obtained.

That is, as shown in FIG. 6, in which parts having the same functions as those in FIG.
For example, a paste prepared by adding powdered glass as the main component, adding appropriate pigments as needed, and adding solvents, binders, etc., is applied to the separation zone by screen printing or the like. The insulating layer 31 is formed by firing later.

In this case, the annealing process for the phosphor layer 13 can also be used as the baking process for the insulating layer 31, making the formation of the insulating layer 31 extremely easy.

Although FIG. 6 shows an example in which the insulating layer 31 is disposed on the upper surface of the substrate 12, the transparent electrode 12 is common to each segment portion or dot portion, and the phosphor layer 15
Alternatively, when only the back electrode 16 is formed in segments or dots, the insulating layer 31 is separated from the transparent electrode 1.
2 or the upper surface of the phosphor layer 13.

Furthermore, in this FIG. 6, 32 is a protective layer formed by resin coating, and 33 is a switch for controlling the light emission of each light emitting part.

In addition, the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist.

As described above, on the top surface of the EL device and round transparent substrate according to the present invention, at least a transparent electrode, a phosphor layer added with an activator, a conductive layer, and a conductive layer are formed on the surface to reduce the It has a structure in which a phosphor layer made of resistive phosphor powder and a back electrode are laminated. Therefore, in the EL device according to the present invention, even if a pinhole portion occurs due to local dielectric breakdown in the portion of the light emitting layer to which a high electric field is applied, the phosphor layer forming the second phosphor layer thereon can be Since the light powder particles have a function of emitting light and automatically repairing it immediately, the applied voltage can be sufficiently large compared to conventional thin film type EL devices, and the luminance can be significantly improved. It has extremely excellent performance features such as stable light emitting operation, and the practical effects obtained are extremely large.

Furthermore, the EL device according to the present invention can operate stably and have a long lifespan without the risk of, for example, Cu ions diffusing into the emitting phosphor or other impurities that inhibit light emission. It is an extremely excellent device that solves the problems of conventional EL devices, especially as an EL device driven by a DC power source, and is expected to have a great effect on expanding the field of use.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining a conventional powder-type electroluminescence device, and FIG. 2 is a schematic diagram illustrating an embodiment of the electroluminescence device according to the present invention.
FIG. 3 is a diagram schematically showing phosphor particles constituting the phosphor layer in the same example, and FIGS. 4, 5, and 6 are diagrams showing other electroluminescent devices according to the present invention. FIG. 2 is a main part configuration diagram showing an example. 11... Substrate, 12... Transparent electrode, 13, 15...
- Phosphor layer, 14...conductive layer, 16...back surface 31...insulating layer.

Claims (1)

[Claims] 1. A transparent substrate comprising at least a transparent electrode, a first phosphor layer added with an activator, a conductive layer, and a phosphor powder, the phosphor powder being disposed on the upper surface of a transparent substrate. An electroluminescent device characterized in that it has a structure in which a second phosphor layer whose surface is coated with a conductive film to reduce resistance and a back electrode are laminated in sequence. 2. The electroluminescent device according to claim 1, wherein the first phosphor layer is a thin film made of a II-VI group compound doped with an activator. 3. The electroluminescent device according to claim 2, wherein the II-VI group compound is ZnS. 4. The conductive layer is made of copper sulfide.
Electroluminescent device as described in Section 1. 5. The electroluminescent device according to claim 1, wherein the second phosphor layer comprises a phosphor powder made by coating phosphor particles doped with an activator and coated with copper sulfide. 6. The electroluminescent device of claim 5, wherein the second phosphor layer comprises a binder. 7. The electroluminescent device according to claim 1, wherein at least one of the transparent electrode and the back electrode is divided into segments or dots. 8. The electroluminescent device according to claim 1, comprising an insulating layer having segment-shaped or dot-shaped openings on the upper surface of either the substrate, the transparent electrode, or the first phosphor layer. .