JPH0278190A - Organic dispersion type el element - Google Patents

Abstract

PURPOSE:To improve the degree of freedom of the luminous color of an organic dispersion type EL element by dispersing a fluorescent material having the color to be changed by the frequency of the electric field and being excited by the outer light to emit the light, in a luminous layer, adding to an EL light emitting material which emits the light by applying of the AC electric field. CONSTITUTION:A luminous layer 3 is provided between a transparent electrode 2 and a counter electrode 5 respectively formed on a translucent insulating substrate 1, through an insulating layer 4, and the whole is covered with a moisture proof protective film 6 so as to form an EL element. In the luminous layer 3, adding to an EL light emitting material 7 which emits the light by applying of the AC electric field, a photoluminescent fluorescent material 8 having a light absorbing end in the area of a light emitting spectral changed by the frequency of AC electric field applied to the fluorescent material 7 and being excited to show the light emitting is dispersed. By changing the quantity and the distribution to the EL fluorescent material and the frequency of the electric field, or using a filter or the like, the degree of freedom of the luminous color can be improved without the problem of the fading.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an organic dispersion type electroluminescent device (hereinafter referred to as an EL device), and is particularly suitable for use in surface light sources, display devices, illuminations, etc. It is something.

[Conventional technology]

FIG. 1 shows a cross-sectional configuration diagram of an EL element according to the present invention, and a conventional organic dispersion type EL element will be explained with reference to this figure. 1 is a translucent insulating substrate made of glass, plastic, or the like. A transparent electrode 2 is formed inside the transparent insulating substrate 1, and is made of a thin film of metal or metal oxide. 3 is a light emitting layer, which is a layer in which light emitting powder is dispersed in an organic binder. 4 is an insulating layer, which is a layer in which dielectric powder such as titanium oxide or barium titanate is dispersed in an organic binder. Reference numeral 5 denotes a counter electrode paired with the transparent electrode 2, which is made of metal foil, metal thin film, or conductive powder dispersed in an organic binder. These layers are sequentially laminated and covered with a moisture-proof protective film 6 made of trifluorochloroethylene or the like. In such an organic dispersion type EL element, by applying an alternating current voltage between the transparent electrode 2 and the counter electrode 5, an electric field is applied to the light emitting layer 3, causing the phosphor powder to emit light. The color of the emitted light at this time is determined by the phosphor powder dispersed in the light emitting layer 3. For example, zinc sulfide-based ZnS:Cu, C1 has a blue color, Zn
For S: Cu and AI, the color is green; for ZnS; Cu and Mn, the color is orange.

[Problems to be Solved by the Invention] By the way, in order to obtain the predetermined emission colors required by such an organic dispersion type EL element, it is necessary to develop a phosphor that emits each of the required emission colors, and this is not practical. do not have. For example, there is a very high demand for the emitted light color to be white, and in order to obtain the required predetermined emitted color, conventional methods have been proposed.

For example, as disclosed in Japanese Patent Application Laid-Open No. 5E1108692, the light-emitting layer 3 is formed using a phosphor obtained by mixing two or more types of phosphors with different emission colors in an appropriate ratio,
How to obtain a given luminescent color.

For example, as disclosed in JP-A-63-19796, a fluorescent dye is dispersed in the light-emitting layer 3, and a predetermined luminescent color is produced by mixing the luminescence from the phosphor powder and the fluorescence from the fluorescent dye. How to get.

■To obtain a blue-green luminescent color, the frequency of the alternating current electric field applied to the phosphor is changed to obtain a luminescent color ranging from green to blue.

In addition, in the method (■), phosphors that emit blue, green, and orange colors are mixed in an appropriate ratio,
In the method (2), a white-emitting organic dispersion type EL element has been put into practical use with a device in which a light-emitting layer 3 is formed, and a phosphor powder that emits green light and a fluorescent dye that emits red light when excited by green light are dispersed in the light-emitting layer 3. has been done.

However, these methods have the following problems.

Method (2) requires multiple phosphors to obtain the required predetermined luminescent color, but the phosphor that emits red light is
It has not yet been put to practical use, and many luminescent colors cannot be expected. Further, the luminance of the organic dispersion type EL element formed by this method is limited by the lowest luminance per volume among the phosphors used. In addition, when an electric field is applied to a phosphor and the phosphor is allowed to emit light, the emitted light intensity gradually decreases with driving time. The speed at which the luminous intensity decreases varies greatly depending on the phosphor, so it has drawbacks such as the luminescent color changing with driving time.

Method (2) solves the problems of method (2) above to some extent, but when the organic dispersion type EL element of this method is driven, part or all of the fluorescent dye may fade or the fluorescent dye may be added. This method has disadvantages such as the speed at which the luminescence intensity of the phosphor powder decreases.

In method (2), the color of the emitted light changes from green to blue as the frequency of the applied alternating current electric field increases from low to high. This phenomenon is almost unaffected by the voltage and waveform of the applied alternating voltage, and shows a -like tendency. This phenomenon is explained as follows. Focusing on any one period of the applied AC voltage, at low frequencies, the electrons and holes generated in the first half period will have enough time for the applied electric field to reverse in the next half period. Therefore, the impurity level gradually becomes trapped. The electrons generated in the first half cycle when the applied electric field is reversed in the next half cycle.

The holes recombine and emit light, but the emitted light has low energy because it is captured in a deep level, and the green light component increases. In the case of high frequencies, the electric field is reversed in the next half cycle before the electrons generated in the first half cycle are captured in deep impurity levels, so they are emitted compared to the case of low frequencies. The light becomes high energy and the blue light component increases.

By utilizing this phenomenon, several luminescent colors can be obtained with a single element by changing the frequency of the AC voltage applied to the organic dispersion type EL element, but even if a filter is used, the luminescent color cannot be changed. The problem is that it is limited to only a few colors, such as from blue to green.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and provide an organic dispersion type EL element with a large degree of freedom in emitting color.

[Means to solve the problem]

In order to achieve the above object, claims 1 and 2 of the present invention
Here, in an organic dispersion type EL element formed on a light-transmitting insulating substrate and having at least a light-emitting layer between a transparent electrode and a counter electrode, light is emitted by applying an alternating current electric field to the light-emitting layer. PL phosphor that exhibits phosphor and photoluminescent that emits light when excited by external light (hereinafter referred to as PL).

) The structure is such that the phosphor is dispersed to produce a predetermined luminescent color.

Further, in claim 3 of the present invention, in an organic dispersion type EL element in which at least a light emitting layer is provided between a transparent electrode and a counter electrode formed on a transparent insulating substrate, an alternating current electric field is applied in the light emitting layer. In addition to the PL phosphor that emits light when applied with a The photoluminescent phosphor is dispersed and a predetermined luminescent color is generated by changing the frequency of the electric field.

[Effect]

Such an organic dispersion type EL element exhibits an emitted light color that is a mixture of light emitted from the PL phosphor and light emitted from the PL phosphor.

Using phosphors also reduces the problem of fading. Also P
Organic dispersed EL elements that exhibit various luminescent colors can be produced without changing the phosphor powder used, depending on the ratio of L phosphor and PL phosphor dispersed in the emissive layer, or the distribution of the dispersion in the emissive layer. You can get it. Of course, it goes without saying that any luminescent color can be obtained by selectively using a plurality of PL phosphors and PL phosphors.

In addition, if the light absorption edge of the PL phosphor exists in a region where the emission spectrum of the PL phosphor changes depending on the frequency of the applied alternating current electric field, the PL phosphor
The PL phosphor absorbs a portion of the light component having energy higher than the light absorption edge of the phosphor, and the PL phosphor emits light. When the frequency of the applied alternating current electric field is increased to increase the high-energy light component of the emission spectrum of the PL phosphor, the emission intensity of the PL phosphor increases and the emission color approaches that of the PL phosphor alone. Conversely, when the frequency is lowered, the high-energy components of the emission spectrum of the PL phosphor decrease, the emission intensity of the PL phosphor also decreases, and the emission color approaches that of the EL phosphor alone. Even in this case, multiple types of PL
An organic dispersion type EL element having a predetermined emission color change range can be obtained by mixing a phosphor and a PL phosphor in an appropriate ratio or using an appropriate filter or the like.

〔Example〕

The present invention will be described below based on embodiments shown in the drawings. 1st
As shown in the figure, a transparent electrode 2 is provided on one side of a transparent insulating substrate 1.
form. The PL phosphor 7 emits blue-green light.
(e.g. Sylvania #813) and a PL that emits red light.
Phosphor powder mixed with phosphor 8 (e.g. Kasei Optonics LDP-R2) in an arbitrary ratio is mixed with an organic binder (e.g. Shin-Etsu Chemical CR-3) at a weight ratio of 70 to 90% and made into a paste. Screen print the luminescent layer 3.
(30 to 100 μm thick). Next, add B, T to the organic binder! 03 powder 70-95% by weight
The mixture is similarly screen printed to form insulation N4 (thickness 5-30 μm).

Next, a counter electrode 5 is formed by screen printing a silver paste and hardening it by heating. The entire structure is covered with a moisture-proof protective film 6 to form an organic dispersion type EL device as shown in FIG.

In the above configuration, the mixing ratio of the PL phosphor in the phosphor dispersed in the light emitting layer 3 is 0 to 75% (A...0%,
B...25%, C...38%, D...62%, E
. . 75%), an organic dispersion type EL device was obtained which emitted light from blue-green to yellowish white, as shown in the known chromaticity diagram of FIG.

Next, a second embodiment of the present invention will be described using FIG. 4.

On a transparent insulating substrate 1 on which a transparent electrode 2 is formed, a paste is prepared by mixing an organic binder with an EL phosphor 7 (e.g. Sylvania #814) that emits blue light at a weight ratio of 80%. , screen printed to a thickness of 40 μm. After curing, the organic binder is coated with a PL phosphor 8 that emits red light (for example, chemical optonics LDP).
- R2) was mixed at 80% by weight, and the thickness was 20 μm in the same way.
A light emitting layer 3 was formed by screen printing.

Thereafter, an organic dispersion type EL device was formed using the same procedure as in the first example, and the organic dispersion type EL device thus obtained was
As shown by ■ in the chromaticity diagram of FIG. 3, purplish blue light was emitted.

Next, a third embodiment of the present invention will be described based on FIG. An EL phosphor 7 (for example, Sylvania #8) that emits blue light is placed on a transparent insulating substrate 1 on which a transparent electrode 2 is formed.
14) is mixed with 33% by weight of PL phosphor 8 (e.g. Kasei Optonics LDP-R2) that emits red light, and mixed with 80% by weight of organic binder,
The paste was screen-printed to form a light-emitting layer 3. Thereafter, an organic dispersion type EL device was formed in the same manner as in the first example. The organic dispersion type EL device thus obtained emitted white light as shown in (■) in FIG.

Next, a fourth embodiment of the present invention will be described using FIG. 5. On a transparent insulating substrate 1 on which a transparent electrode 2 is formed, a PL phosphor 8 that emits red light (e.g., Kasei Optonics LDP-R2) is mixed with an organic binder at a weight ratio of 80%, and a paste is formed. This was screen printed to a thickness of 20 μm. After curing, an EL phosphor 7 that emits blue light (for example, Sylvania #814) was mixed with the organic binder in an amount of 80% by weight, and the mixture was similarly screen printed to a thickness of 40 μm to form a light emitting layer 3. Thereafter, an organic dispersion type EL device was formed using the same procedure as in the first example. The organic dispersion type EL device obtained in this way is as shown in ■ in Figure 3.
It emitted greenish white light. In this way, as shown in the second to fourth embodiments, the color of the emitted light can be controlled even if the distribution state of the EL and PL phosphors is changed.

The PL phosphor used in the present invention is an organic dispersed E
Among the materials that have sufficient insulation under the electric field applied to the L element and satisfy the condition that the energy of the optical basis absorption edge of the phosphor powder shown in Figure 6 is smaller than the emission energy of the EL phosphor. selected from.

Next, the fifth embodiment of the present invention will be described in FIGS. 1 and 7 to 1.
This will be explained based on FIG. As shown in Figure 1, the weight ratio of EL phosphor 7 (Sylvania #813), which emits blue-green color, to an organic binder (Shin-Etsu Chemical CR-3) is 75%.
% mixed and made into a paste and screen printed.
A light emitting layer 3 is formed (thickness: 80 μm). Next, BaTi0
．． A mixture of powder and organic binder at a weight ratio of 80% was similarly i-clean printed to form insulation N4.

Next, silver paste was screen printed and cured by heating to form a counter electrode 5, and the whole was covered with a moisture-proof protective film 6, thereby producing an organic dispersion type EL element. Through these steps, a 60ovp-p square wave was applied to the fabricated EL element, and the frequency was adjusted to 50Hz to IKHz (1=50Hz, 2-10
0Hz, 3-200Hz, 4=-400Hz, 5-IK
Hz), the emission spectrum in Fig. 7 and Fig. 8
The luminescent color changed as shown in the chromaticity diagram in the figure.

In addition to the blue-green light-emitting EL phosphor that exhibits these characteristics, there is a red-light-emitting PL phosphor (Kasei Optonics LDP-R) that exhibits the light absorption edge shown in Figure 9 and the emission spectrum characteristics shown in Figure 10.
2) at a weight ratio of 50%, and this mixed phosphor was mixed with an organic binder at a weight ratio of 80%, and the above transparent electrode 2
A light-emitting layer 3 was formed on the transparent insulating substrate 1 on which a light-emitting layer 3 was formed by screen printing in the same manner. Thereafter, an organic dispersion type EL device having the structure shown in FIG. 1 was formed using the same procedure as above.

A square wave was applied to the EL element produced in this way, and the frequency was adjusted to 50Hz to IKHz (1-50Hz).

2=100Hz, 3--200Hz, 4-400Hz.

5...IKHz), a color change was shown as shown in the emission spectrum of FIG. 11 and the chromaticity diagram of FIG. 12.

Next, as a sixth example, a color filter having the light transmittance spectrum shown in FIG. An organic dispersion type EL device having the structure shown in FIGS. 14(a) and 14(b) was formed. When a square wave of 50H2 was applied to the EL element fabricated in this way, the part where the color filter was not attached emitted bright green light, and the part where the color filter 9 was attached emitted extremely dark red light, and the overall result was , a display of black characters on a green background was obtained. Next, when an IKHz square wave was applied, the non-device part of the color filter 9 emitted bright white light, the device part of the color filter 9 showed red light emission, and as a whole, red letters were displayed on the white background. was obtained. This display color changes continuously by changing the frequency of the applied square wave between 50 Hz and IKHz.

Next, an example of a drive circuit for an organic dispersion type EL element according to the fifth and sixth embodiments will be explained using FIG. 15. In order to change the emission color of this organic dispersion type EL element, it is necessary to change the frequency of the applied AC voltage. Note that the luminance of the organic dispersion type EL element changes depending on the frequency of the applied alternating current voltage, and as the frequency becomes lower, the luminance of the luminescence decreases. Therefore, if the emission color is made variable by controlling only the frequency, the emission brightness will change, so it is preferable to compensate for the change in the emission brightness by some method.

Therefore, in this example, the luminance of the organic dispersion type EL element changes depending on the voltage value of the applied AC voltage, and the higher the voltage, the higher the luminance, and the accompanying change in the luminescent color is slight. By controlling the voltage value in conjunction with controlling the frequency to be applied, changes in luminance of light emission are compensated for. In other words, the applied voltage is controlled to be high when the frequency is low, and low when the frequency is high.

The switching transistors Tr1 to Tr4 are controlled by the square wave generated by the oscillation circuit 10, and a square wave applied voltage is generated. At this time, an alternating current voltage is applied to the EL element 20 by applying signals having the opposite phase to T□ and Trz to Tr3 and Tr4. The voltage is the DC voltage applied to the switching transistors T,1 to T I'4.
It is controlled by a variable voltage DC voltage source consisting of ri and an error amplifier 30. By controlling the oscillation frequency of the oscillation circuit and the variable voltage DC voltage source by the control circuit 40,
Desired emission brightness and emission color can be obtained.

In the above-described embodiments, the PL phosphor is not limited to an inorganic phosphor, and may be anything that emits light when excited by external light, such as an organic fluorescent dye.

〔Effect of the invention〕

As detailed above, according to claim 1 of the present invention, a predetermined luminescent color that cannot be obtained with EL phosphors alone can be obtained, and since no fluorescent dye is used, there is no problem of fading, which is an excellent effect. be. According to claim 2 of the present invention, the organic dispersion type EL exhibits more luminescent colors by controlling the mixing ratio or distribution of a plurality of phosphors dispersed in the light emitting layer.
The device can be easily obtained.

Furthermore, according to claim 3 of the present invention, it is possible to realize an organic dispersion type EL element having a desired emission color change range.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram showing the structure of a first embodiment of an organic dispersion type EL device according to the present invention, FIG. 2 is a chromaticity diagram of emitted light color in the first embodiment, and FIG. 3 is a diagram of the invention. The second example of ~
Chromaticity diagram of emitted light color in the fourth embodiment, FIG. 4 is a cross-sectional explanatory diagram showing the structure of the second embodiment of the present invention, and FIG. 5 is a cross-sectional diagram showing the structure of the fourth embodiment of the present invention. An explanatory diagram, FIG. 6 is a characteristic diagram of the light transmittance of the PL phosphor used in the first to fourth embodiments of the present invention, and FIGS. 7 and 8 are explanations of the fifth embodiment of the present invention. FIGS. 9 and 10 are an emission spectrum diagram and a chromaticity diagram of an EL phosphor used for explaining the fifth embodiment. Figures 11 and 12 are the emission spectrum diagram and chromaticity diagram of the fifth example, Figure 13 is a diagram showing the light transmittance of the color filter used in the sixth example of the present invention, and Figure 14 ( a) and (b) are a sectional view and a plan view showing the structure of the sixth embodiment, and FIG. 15 is a diagram showing the drive circuit used in the fifth and sixth embodiments. 1... Transparent insulating substrate, 2... Transparent electrode, 3...
Light emitting layer, 4... Insulating layer, 5... Counter electrode, 6...
Moisture-proof protective film, 7...EL phosphor, 8...PL
Phosphor, 9... Color filter, 10... Oscillation circuit, 20... EL element.

Claims (3)

[Claims] (1) In an organic dispersed EL element in which at least a light emitting layer is provided between a transparent electrode formed on a transparent insulating substrate and a counter electrode, light is emitted by applying an alternating current electric field to the light emitting layer. 1. An organic dispersion type EL device characterized in that an electroluminescent phosphor that exhibits a luminescent color and a photoluminescent phosphor that emits light when excited by external light are dispersed to produce a predetermined luminescent color. (2) A claim characterized in that the electroluminescent phosphor and the photoluminescent phosphor are dispersed in the light emitting layer at a predetermined mixing ratio or distribution state to produce the predetermined luminescent color. Item 1. The organic dispersion type EL device according to item 1. (3) In an organic dispersion type EL element in which at least a light-emitting layer is provided between a transparent electrode and a counter electrode formed on a transparent insulating substrate, light is emitted by applying an alternating current electric field to the light-emitting layer. and a photoluminescent phosphor that has an optical absorption edge within a region of the emission spectrum that changes depending on the frequency of an electric field applied to the electroluminescent phosphor and is excited by external light. An organic dispersion type EL device characterized in that the organic dispersion type EL device is made to emit light of a predetermined color by dispersing the electric field and changing the frequency of the electric field.