JPH0416791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a lighting method for an electroluminescent (hereinafter referred to as EL) element capable of displaying multiple colors.

B. Prior Art Currently, thin-film EL devices can emit light in orange, green, blue, red, and other colors depending on the type of activator used. However, since all of these are monochromatic lights, there is a conventional thin film EL element 1 shown in FIG. 1, which has attempted to provide multicolor light.
That is, although FIG. 1 is a cross-sectional view of the thin film EL element 1,
In the figure, 2 and 3 are luminescent layers to which different activators are added, and 4a, 4b, 4c, and 4d are insulating layers.The luminescent layer 2 is sandwiched between the insulating layers 4a and 4b, and emits light. Layer 3 is sandwiched between insulating layers 4c and 4d. 5 is a metal electrode such as Al, 6a,
6b is ITO (Indium Tin Oxide) such as In ₂ O ₃ ,
The metal electrode 5 and the transparent electrode 6a sandwich the insulating layers 4a and 4b, and the transparent electrode 6 is made of Sn ₂ O ₃ or the like.
a and 6b sandwich the insulating layers 4c and 4d. That is, the thin film EL element 1 includes a monochromatic light emitting thin film EL element 7 consisting of a light emitting layer 2, insulating layers 4a and 4b, and electrodes 5 and 6a;
A monochromatic light emitting thin film EL element 8 consisting of a light emitting layer 3, insulating layers 4c and 4d, and electrodes 6a and 6b are laminated. Since the thin film EL elements 7 and 8 emit light of different colors, between the opposing electrodes 5 and 6a,
By applying voltage separately or simultaneously between the electrodes 6a and 6b, the color of the emitted light can be changed, or a mixed color thereof can be obtained.

Similarly to the above, by stacking two or more sets of monochromatic light emitting layers while inserting a transparent electrode in the middle, it becomes possible to make the thin film EL element multicolored.

However, in such conventional multi-color attempts, when stacking multiple light-emitting layers, it is necessary to insert transparent electrodes in the middle, which increases the number of manufacturing steps and electrodes each time the number of light-emitting layers is increased. The problem was that as the number of devices increased, the structure and circuits gradually became more complex.

C. Purpose of the Invention The purpose of the present invention is to utilize the fact that the EL emission intensity is distributed in the thickness direction of the light emitting layer and that the distribution depends on the polarity of the applied voltage, to provide an EL device that emits light of up to three colors. The present invention aims to provide a method for lighting an element.

D. Structure of the Invention The method for lighting a thin film EL device according to the present invention is such that, in a device in which at least a phosphor layer is sandwiched between opposing electrodes, when a unipolar voltage is applied between the opposing electrodes, the maximum electric field strength and The first phosphor layer is
A light-emitting layer with a second light-emitting color is interposed between the opposing electrodes, and a light-emitting layer with a second light-emitting color is interposed in the portion of the phosphor layer that has the maximum electric field intensity when a voltage of the other polarity is applied between the opposing electrodes. By applying an asymmetrical alternating voltage between the positive and negative sides, the light-emitting layers of the first and second light-emitting colors are caused to selectively emit light.

E. Example The present invention utilizes the experimental results shown in FIGS. 2 and 3 a and b. That is, as shown in FIG.
A pulse voltage V higher than the _threshold voltage (hereinafter referred to as _Vth ) shown in FIG. In this case, the distribution of the emission intensity D of the EL emission becomes non-uniform with respect to the film thickness l, and the third
The curve shown in figure a is obtained. And the same thin film EL
When a pulse voltage with a polarity different from that in FIG. 4a is applied to the element 9 as shown in FIG. 4b, the distribution of the luminescence intensity D of the EL emission is as shown in the curve shown in FIG. 3b with respect to the film thickness l. Become. That is, the EL of the thin film EL element 9
The light emission intensity D of light emission is strongest at a specific location relative to the film thickness l, and the location differs depending on the polarity of the applied voltage.

It can thus be seen that the emission intensity D of the EL emission of the thin film EL element 9 is strongest at two specific locations of the film thickness l depending on the polarity of the applied voltage, and other locations do not significantly contribute to the intensity of the emission. Therefore, in the case of the thin film EL element 9, a light emitting layer of (ZnS:Mn) doped with Mn is formed at the two locations of the thin film EL element 9 where the luminescence intensity is strongest, and the other locations are left as a (ZnS) layer. It is expected that a distribution curve similar to the curves shown in FIGS. 3a and 3b will be obtained. That is, as shown in FIG. 5, two light-emitting layers having different light-emitting colors are placed at the two locations where the light-emitting intensity is the strongest, for example, a (ZnS:Mn) layer that emits orange light and a layer that emits green light (ZnS:Mn). In the case of the thin film EL element 10 in which a TbF ₃ ) layer is formed, the color changes from orange to orange depending on the polarity of the applied voltage.
and green will emit light separately.

That is, a thin film EL element 10 showing an embodiment of the present invention
11a, 11b, and 11c are phosphor layers formed only of ZnS, which are sandwiched between insulating layers 12a and 12b. Reference numeral 13 is a light-emitting layer made of ZnS doped with Mn, and 14 is a light-emitting layer made of ZnS doped with _TbF3 . Layers 11b and 11c are laminated in parallel. 15 is Al
16 is a transparent electrode of ITO.

According to such a configuration, each light emitting layer 13 and 14
between each light emitting layer 13, 14 and each insulating layer 12
a, 12b between each phosphor layer 11a, 11b, 1
Since the area is divided by 1c, by selectively emitting light in the region where the electric field strength is the strongest, it is possible to emit light in a substantially single color.

In the thin film EL element 10, the electrode 15 is positive,
When a voltage equal to or higher than Vth is applied so that the electrode 16 becomes negative, the distribution of the luminous intensity D becomes as shown in Figure 6a, and the luminescent layer 13 of (ZnS:Mn) emits orange light, depending on the polarity of the applied voltage. When reversed, the distribution of emission intensity D becomes as shown in Figure 6b, (ZnS:
The light emitting layer 14 made of TbF ₃ emits green light.

Therefore, if the voltage waveform applied to the thin film EL element 10 is made as shown in FIG.
It emits green in the area, and white, which is a mixture of both, in the W area. That is, in the 0 region of Fig. 7
When a pulse P ₁ higher than Vth is applied, first the thin film
The EL element 10 emits orange light, but since the element forms a capacitor, this occurs after the capacitor is charged, that is, when the electrons that excite Mn in the light emitting layer 13 move from the electrode 16 side to the electrode 15 side. ,
Light emission stops. At this time, electrons are blocked by the insulating layer 12a and do not flow into the circuit. Therefore, in order to emit orange light continuously, it is necessary to change the polarity and apply a refresh pulse voltage _P2 , which is lower than Vth so that green light is not emitted, after applying _P1 . At this time, the electrons return from the electrode 15 to the electrode 16 without exciting TbF ₃ in the light emitting layer 14. If a pulse voltage P ₃ having the same polarity as the pulse voltage P ₁ and higher than Vth is applied after applying P ₂ , the thin film EL element 10 emits orange light again. Therefore, if a voltage waveform in the 0 region is continuously applied to the thin film EL element 10, the thin film EL element 10 continuously emits orange light.

Next, in the G region of FIG. 7, the pulse voltage P ₁ ,
If a pulse voltage P ₄ of Vth or more with the opposite polarity to P ₃ is applied, TbF ₃ in the light emitting layer 14 is excited and the thin film EL
Element 10 emits green light. As above, in order to sustain green light emission, after applying a fresh pulse _P5 smaller than Vth, _P4
It is only necessary to apply the same pulse voltage _P6 to the thin film EL element 10, and if the voltage waveform in the G region is continuously lowered, the thin film EL element 10 continuously emits green light.

Furthermore, if pulse voltages P ₇ , P ₈ , and P ₉ whose polarities alternately change in the W region of FIG. 7 and are higher than Vth are continuously applied, the thin film EL element 10 emits light in orange and green alternately. As a result, white light emission, which is a mixed color, is obtained.

At this time, in order to emit such white light,
When the light emitting layers 13 and 14 are laminated, the thickness of each light emitting layer 13 and 14 and the amount of Mn or TbF ₃ added must be adjusted so that the ratio of each light emitting intensity becomes a predetermined ratio in the viewing direction. No.

Moreover, the driving of each pulse voltage is as shown in Fig. 7.
Although it is possible to suddenly apply a voltage of a predetermined magnitude from OV, a bipolar pulse voltage less than Vth is applied as a bias voltage, and a voltage of a predetermined magnitude is added on top of that as necessary. There is a way. According to such a driving method, the configuration of the driving circuit becomes simple, and, for example, the Vth of the light emitting layers 13 and 14
It is valid when the two are different from each other.

Such a thin film EL device 10 is manufactured by depositing each layer on a glass substrate using an electron beam, and its practical structure is shown in FIG. That is, in FIG. 8, 17 is a glass substrate, 16
is a transparent electrode such as ITO, In ₂ O ₃ , SuO ₂ etc., 12
a, 12b are insulating layers, 11a, 11b, 11c,
13 is a (ZnS:Mn) layer, 14 is a (ZnS:TbF ₃ ) layer, and 15 is a metal electrode such as Al.

Furthermore, as a light-emitting layer, a ZnS phosphor added with rare earth fluoride is known, and as mentioned above, when Mn is added to ZnS, it emits orange light, and when TbF ₃ is added, it emits green light. However, it is also known that adding SmF ₃ to ZnS causes it to emit red light, and adding DyF ₃ to ZnS causes it to emit blue light.
Then, you can choose two colors from among these.

F. Effects of the Invention According to the present invention, the conventional thin film with double insulation structure
In EL elements, without intervening transparent electrodes,
Two light-emitting layers with different luminescent colors are formed, and each of the two light-emitting layers emits light separately depending on the polarity of the applied voltage.The process, number of electrodes, etc. are the same as before, but the drive waveform can be changed. Colorization becomes possible.

[Brief explanation of drawings]

Figure 1 is a cross-sectional schematic diagram of a conventional multicolor display EL element.
Figure 2 is a schematic cross-sectional view of a typical thin film EL device, and Figures 3a and b are the luminous intensity versus thickness of the light emitting layer when the polarity of the applied voltage is changed in the monochromatic light emitting thin film EL element shown in Figure 2. Distribution curve of Figure 4 a, b
are waveform diagrams of applied voltages with different polarities; FIG. 5 is a schematic cross-sectional diagram of an embodiment of a thin film EL element according to the present invention;
Figures 6a and 6b show the fifth part of the thin film EL device according to the present invention.
The emission intensity distribution curve corresponding to the figure shows a curve depending on the polarity of the applied voltage. Figure 7 shows the thin film EL according to the present invention.
FIG. 8, which is a waveform diagram of the driving voltage of the device, is a sectional view of the practical structure of the thin film EL device according to the present invention. 10... Thin film EL element, 11a, 11b, 11
c...fluorescent layer, 12a, 12b...insulating layer, 1
3, 14... Light emitting layer, 15, 16... Counter electrode.

Claims (1)

[Claims] 1. In a device in which at least a phosphor layer is sandwiched between opposing electrodes, a luminescent layer of a first luminescent color is provided in a portion of the phosphor layer where the maximum electric field intensity occurs when a unipolar voltage is applied between the opposing electrodes. and a light-emitting layer of a second luminescent color is interposed in the portion of the phosphor layer that has the maximum electric field strength when a voltage of the other polarity is applied between the counter electrodes, and an asymmetrical AC voltage of positive and negative polarity is applied between the counter electrodes. 1. A method for lighting an EL device, characterized in that the light-emitting layers of the first and second light-emitting colors are selectively emitted by applying a voltage.