JPH04185692A - El stimulable phosphor - Google Patents

Abstract

PURPOSE:To obtain an EL stimulable phosphor excellent in luminance and capable of low-voltage drive by mixing and dispersing a specific substance in a stimulable phosphor material so that the substance is carried on the material. CONSTITUTION:A radioactive substance (e.g. <232>Th) is mixed with, dispersed in and carried on a stimulable phosphor material (e.g. ZnS-Mn).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an EL phosphor for thin film EL elements used in color displays, area lighting, etc.

[Prior Art] A thin film EL device generally includes a transparent electrode 9, an insulating layer 10, and a phosphor (light-emitting layer) on a glass substrate 8, as shown in FIG.
11, an insulating film 12, and a back electrode 13 are sequentially formed.

In the phosphor II, as shown in Fig. 6, Mn, which is the emission center material dispersed in the ZnS crystal, which is the phosphor material, is excited and accelerated by the accelerated electrons of hot electrons or the impurity level in the photoelectric field. The ionized electrons are ionized and excited to emit EL light.

Therefore, the emission brightness is proportional to the electric field of the phosphor material, the generation rate of hot electrons, and the distribution of emission centers (collision frequency).
Depends on.

[Problem to be solved by the invention] However, the following problems were found.

■ Conventional phosphor materials lack luminance. 7th
As shown in the figure, the saturated luminance has a peak value when the luminescence center material Zn concentration is around 0.4 wt%. this is,
There is a limit to the rate of generation of hot electrons from phosphors.
This is because even if there is more luminescent center material, it will not contribute to luminescence, and if there is more than necessary, it will also inhibit luminescence.

■ Conventional high-voltage drive lacks luminance. 8th
The figure shows the correlation between voltage and luminance, and the threshold value is 19
It is 5V or more, and the luminance is proportional to the voltage, but it is 230V
The above is a plateau region.

An applied voltage of about 210 V is required, and the brightness does not improve any further even with a high voltage. This is because the generation rate of hot electrons is unique to the phosphor and has a limit. The lack of luminance in (2) and (2) is particularly noticeable in blue.

■ ICs and circuits driven by high voltages are expensive because high electric fields are applied to the elements, and applying high voltages to the elements can cause them to break down, reducing reliability.

The present invention aims to solve the above-mentioned problems, and its purpose is to provide an E
The purpose of the present invention is to provide an L phosphor.

[Means for Solving the Problems] The EL phosphor of the present invention is characterized in that a radioactive substance is mixed and dispersed and supported in the phosphor material.

Next, the present invention will be explained in detail.

FIG. 1 shows an equivalent circuit of an EL element.

200V between the transparent electrode (CITO) and the back electrode (8β)
When an AC voltage of 50 to 60 Hz is applied to the
A partial pressure is applied to 0 (Ω3), and the Ω2 partial pressure accelerates hot electrons and excites electrons at an impurity level in the phosphor material by collision. When the threshold value is exceeded, ions are formed in the conduction band with electrons as impurity centers. Electrons accelerated and excited in the conduction band recombine with the impurity center and emit light with a wavelength corresponding to its energy.

Furthermore, the electrons excited in the conduction band are further accelerated by a high electric field, collide with the luminescent center material, and are excited and ionized. Furthermore, the electrons in the conduction band recombine with the luminescent center ion,
It emits light at a wavelength equal to the gap energy between the emission center level and the conduction band.

That is, EL has a combined wavelength of light emission from the phosphor material and light emission from the emission center material. Therefore, various emitted colors can be obtained by selecting the material.

As the phosphor material used in the present invention, conventional materials are used, such as ZnS, CaS, SnS, etc. Further, examples of luminescent color-centered materials used in the present invention include Mn, SmFi, Eu, TbFx,
Examples include Le, K, TmFa, and the like. A suitable combination of the phosphor material and the luminescent center material is as follows:
ZnS:Mn, ZnS:SmFs, CaS:Eu, Z
nS:TbF, ,CaS:Ce, ZnS:TmF
s, SrS:Ce, SrS:Ce, etc.

Examples of radioactive substances used in the present invention include 232
For example, Th. The thorium series shown in Fig. 2 includes a radioactive decay series, so if Th is dispersed and supported on the phosphor, the thorium series will be 4.007 to 8.78M from xsaTh.
It emits eVOa rays and β rays of 0.012 to 2.27 MeV. These α and β rays have a strong ionizing effect and form many electron-ion pairs within the crystal.

Furthermore, since the alpha ray is a He nucleus, its range in the phosphor material is small, and since it is a cation, impact ionization occurs during its small range, causing its energy to be attenuated.

Therefore, a large number of pairs of electrons and ions are generated.Also, since β-rays are high-energy electrons, their range is greater than that of α-rays. Similarly, β-rays generate many pairs of electrons and ions during their range. Form ion pairs. Even if a radioactive substance does not have a decay series, it is 1iEl if it emits α or β rays! (Since it has a large capacity, it can be used in the present invention.)

Since there are electrons and ion pairs in addition to hot electrons generated in the phosphor, the presence of an accelerating electric field also increases the number of accelerated electrons.

In addition, since the energy of the electrons generated from radioactive substances is very large, there are those that directly excite the impurity level electrons of the phosphor, those that recombine, and those that directly excite the emission center. The amount (radioactivity concentration) varies depending on the type of phosphor material and luminescent center material, but there is an appropriate amount value.

If the radioactivity concentration is high (the phosphor will emit light even in the absence of an electric field).

In addition, by forming a composite compound of a luminescent center material and a radioactive substance and dispersing it in a phosphor, there are many excited electrons near the luminescent center, which intensifies the EL emission mainly from the luminescent center. The width of the emission vector becomes sharper.

Figures 3(a) and 3(b) show structural models in the phosphor. Figure 3 (a) shows a radioactive element (Th) and a luminescence center material (Mn) uniformly dispersed in a phosphor material (ZnS), and the effect of the radioactive element affects both the phosphor material and the luminescence center material. It is something.

Figure 3 (b) shows a composite compound of a radioactive element and a luminescent center material (Mn) that is later dispersed in a phosphor material (ZnS), which mainly gives the effect of the radioactive element to the luminescent center material. .

[By creating a phosphor that carries radioactive substances in a dispersed manner,
In addition to the generation of hot electrons, electrons and ions are generated due to the ionizing effect of radiation, which excites the luminescent center material (
The amount of collision) increases, and therefore the luminance of the light emitted increases. Further, even if the concentration of the luminescent center material added is increased to 0.4 wt % to 1%, the luminance is improved.

In addition, accelerated electrons associated with hot electrons from the phosphor are generated above the threshold voltage, but when radioactive substances are present, electrons and ions are always present within the phosphor.
Electron excitation is possible even at low voltages, lowering the threshold voltage.

That is, by including a radioactive substance in the phosphor, the luminance of light emission is improved and low voltage driving becomes possible.

Furthermore, high brightness can be obtained even more efficiently by creating a composite compound by reacting the emission center material and the radioactive material and dispersing this in the phosphor.

[Example] Next, the present invention will be explained by giving examples.

Example 1 Water is added to 99 parts by weight of ZnS phosphor powder, 0.2 to 1 part by weight of MnS powder, and 1 to 1.8 parts by weight of Th, S, powder, and kneaded in a ball mill to obtain a gel-like material.

Transparent electrode 2 (ITO 1 film thickness 0.1μ) on glass substrate 1
m), insulating film 3 (Sio2 or SiN, film thickness 0.1
~0.5 μm) (Fig. 4(a)), and then the gel-like material is patterned on this using screen printing etc. (Fig. 4(b)), at this time the film thickness is 0. The thickness should be approximately .5 to 2 μm. Thereafter, the phosphor 4 is obtained by preliminary drying and baking at 300 to 600° C. for 2 to 5 hours in an N2, H2S atmosphere.

After that, an insulating film 5 (Siow or SiN,
The EL element 7 is obtained by forming a film thickness of 0.5 to 1 μml (FIG. 4(C)) and then a back electrode 6 (Ar2) (FIG. 4(d)).

Example 2 After mixing the phosphor material of Example 1, the powder was press-molded,
A target for sputtering is prepared by baking at 400° C. for 3 hours in an N, H, S atmosphere. A transparent electrode 2 is placed on a glass substrate 1. After forming the insulating film 3, using this target, a phosphor 4 is formed on the insulating film by sputtering in an H, S atmosphere using Ar as a sputtering gas.

Thereafter, in the same manner as in Example 1, the insulating film 5. Back electrode 6
is formed to obtain the EL element 7.

[Effects of the Invention] As is clear from the above description, according to the EL phosphor of the present invention, it is possible to obtain an EL element that can efficiently obtain sufficient luminance and can be driven at a low voltage.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the equivalent circuit of an EL element, Fig. 2 is an explanatory diagram showing the radioactive decay of dust, and Fig. 3 (a) is an explanatory diagram showing a structural model of an example of the present invention in a phosphor. Figure, Figure 3 (
b) is a diagram showing a structural model in the phosphor of the other side of the present invention, and FIGS. 4(a) to (d) show the manufacturing process of an EL element using the phosphor of one embodiment of the present invention. 5 is a sectional view showing the structure of a general EL element, FIG. 6 is a sectional view showing a structural model in a conventional phosphor, and FIG. 7 is an EL element using a conventional phosphor. FIG. 8 is a graph showing the relationship between the luminescent center material concentration and the saturated luminance, and FIG. 8 is a graph showing the relationship between the applied voltage and the luminance. DESCRIPTION OF SYMBOLS 1... Glass substrate, 2... Transparent substrate, 3... Insulating film, 4... Phosphor, 5... Insulating film, 6... Back electrode, 7... EL element, 7 ...Glass substrate, 9...
Transparent electrode, 10... Insulating film, 11... Fluorescent material, 12
... Insulating film, 13... Back electrode. Applicant Rico Co., Ltd. - Figure 1 Figure 2 Zn S Zn S Zn S Zn S Zn S Zn 5 (b) Figure 3 (a) (b) (C) (d) Figure 4 Figure 5 Zn S Zn S Th S Zn S Figure 6 Figure 7 Figure 8

Claims (2)

[Claims] (1) An EL phosphor characterized in that a radioactive substance is mixed and dispersed and supported in a phosphor material. (2) The EL phosphor according to claim 1, wherein the radioactive substance is mixed with a luminescent center material to form a composite compound, which is dispersed and supported in the phosphor material.