JPH09255952A - Phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phosphor having a capability of emitting light even at a low voltage and contg. as the matrix SrTiO3 having good life span properties. SOLUTION: There is prepd. an SrTiO3 : Pr, Al phosphor activated with 0.0025mol/mol of Pr and admixed with 0.2mol/mol of Al. The phosphor is coated with Pt chloride dissolved in a predetermined amt. of ethanol, and fired at a temp. of 400 to 700 deg.C to convent the substance coating the phosphor into an oxide, PtO2-x (wherein 0<=x<2). The amt. of coat was varied in the range of 10 to 80,000μg/g. A vacuum fluorescence display having the phosphor mounted on the anode thereof was produced to evaluate the light emission thereof at an anode voltage of 400V and at an anode current of 75mA/cm<2> . STD stands for the phosphor not subjected to surface treatment. The residual luminamnce rate, which indicates the life span, is increased as the amt. of coat is increased. The residual luminance rate of STD with no coat is 20% in terms of relative value. A phosphor wherein the amt. of coat is about 500μg/g shows a relative illuminance of at least 70%, which is more than 3 times as much as that of STD. The amt. of coat is most pref. in the range of 800 to 2,000μg/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent display tube, a fluorescent display device using a field emission device as an electron source, and the like. The present invention relates to a fluorescent substance that emits light.

[0002]

2. Description of the Related Art SrTiO ₃ : Pr, Al phosphors have an energy gap of 3.3 eV and a low matrix resistance. Therefore, when electrons are bombarded, red emission is observed from the stage of low accelerating voltage. .

[0003]

DISCLOSURE OF THE INVENTION The inventors of the present invention evaluated the life of the phosphor by using this phosphor as an anode of a fluorescent display tube. Luminance of the phosphor deteriorated after several tens of hours. At this time, the surface of the phosphor was colored black. Surface analysis showed an increase in carbon. When the same phosphor was subjected to life evaluation in a demantable apparatus that irradiates an electron beam in an ultra-vacuum atmosphere, it was found that the phenomenon such as the increase in carbon as described above is unlikely to occur.

Further, when the phosphor is manufactured, Sr / Ti
Even if the ratio, Al and Pr contents were changed, there was almost no effect in improving the life characteristics. Furthermore, mixing the powder of a conductive material such as InO ₃ and WO ₃ did not improve the basic life characteristics.

The inventors of the present application made the following consideration on the cause of the deterioration of the lifetime of the phosphor, based on the above new findings obtained from the experiments. First, when the phosphor is excited by electron beam bombardment in the vacuum container to emit light, it is considered that various reactions occur with the residual gas in the vacuum container on the surface of the phosphor. Generally, the surface of the phosphor is considered to be cleaned at this time, but it was found that the reverse phenomenon occurs with some phosphors.

It is said that 90% or more of the electric power applied to the anode for accelerating electrons in a fluorescent display tube becomes heat as loss energy. For example, since the phosphor has a small energy gap, this loss is caused. The energy intensity is low, the luminous efficiency of the phosphor is high with respect to the input energy, and heat is generated relatively little. Therefore,
The gas component attached to the surface of the phosphor cannot be removed by the loss energy, and the attached gas component is accumulated on the surface of the phosphor.

In particular, it is considered that the surface of the portion irradiated with the electron beam becomes active and the amount of accumulated gas increases. Also, the binding energy of carbon is 4e.
Since it is often V or more, it is considered that gas adsorption is likely to occur in a phosphor having an energy gap of this value or less.

The phenomenon that the carbon-based gas is adsorbed on the phosphor having a small energy gap depends on the material of the phosphor, and among the residual gas components in the vacuum container, the carbon-based gas (CO, CO ₂ , CH ₄ ) and moisture active materials have been found to be particularly pronounced.

That is, in the case of an oxide phosphor containing an alkaline earth metal as a component, for example, Sr-O or Ba is formed on the surface thereof.
There are bonds such as -O. Considering Sr as an alkaline earth metal, for example, at room temperature, SrO + CO ₂
→ It is speculated that a reaction like SrCO ₃ will proceed. Therefore, it is considered that the oxide phosphor containing an alkaline earth metal as a component is particularly sensitive to the carbon-based gas.

When a phosphor containing an alkaline earth metal as a component and having a small energy gap of 4 eV or less is used, the carbon-based gas partial pressure in the vacuum container is 1 × 10 ^-6 Pa or less. However, in the case of a fluorescent display tube, for example, the filament cathode is generally made of carbonate, and it is difficult to reduce the carbon-based gas partial pressure. Also, 1 × 10 ⁻⁶ Pa
The degree of vacuum below is a so-called ultra-high vacuum region, which leads to an increase in cost in manufacturing a device.

It is an object of the present invention to provide a phosphor containing SrTiO ₃ as a host material, which emits light from a low voltage and has good life characteristics.

[0012]

The phosphor described in claim 1 is characterized in that a substance having an oxidizing action is added to the phosphor having SrTiO ₃ as a matrix.

The phosphor according to claim 2 is the phosphor according to claim 1.
In the above-mentioned phosphor, the substance having an oxidizing action is P
It is an oxide containing at least one substance selected from tO _2-x (0 ≦ x <2) and RuO _2-x (0 ≦ x <1).

The phosphor according to claim 3 is the phosphor according to claim 1.
Alternatively, the phosphor according to the aspect 2 is characterized in that the substance having an oxidizing action covers the surface of the phosphor in one of a state selected from a film shape and a fine particle shape.

The phosphor described in claim 4 is the phosphor according to claim 1.
Alternatively, the phosphor according to 2 or 3 is characterized in that the energy gap of the phosphor is 5 eV or less.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that the carbon-based gas partial pressure in a vacuum container is 1 × 10 ⁻⁶ Pa based on the unique knowledge described in the section [Problems to be Solved by the Invention]. As described above, the inventors have earnestly studied the means for stably emitting light by the electron bombardment of the phosphor having SrTiO ₃ as a matrix. As a result, if the surface of the phosphor or the surface of the phosphor layer is surface-treated with a specific substance having an oxidizing action, the surfaces of these phosphors are protected from the gas, and excitation by an electron beam is sufficient. It was found that the emission brightness and lifetime were also obtained. Examples of the substance having an oxidizing action that can obtain such an effect include PtO _2-x (0 ≦ x <2) or RuO _2-x (0 ≦
There are oxides such as x <1).

[0017]

【Example】

(1) Example 1 SrTiO ₃ : Pr, activated with 0.0025 mol / mol of Pr and added with 0.2 mol / mol of Al,
An Al phosphor is prepared. Pt chloride is dissolved in a predetermined amount of ethanol and the phosphor is coated. This is 400 ℃ ~
The substance coated on the phosphor after being baked at 700 ° C. is oxide P
It was set to tO _2-x (0 ≦ x <2). The coating amount is PtO ₂
It was changed to 10 μg / g to 80,000 μg / g.

A fluorescent display tube was prepared by mounting the above-mentioned phosphor coated with the above substance on the anode of the fluorescent display tube, and the fluorescent display tube was made to emit light for evaluation. The lighting condition is that the anode voltage is 400
V and the anode current were 75 mA / cm ^{2 on} average.
The phosphors not subjected to the surface treatment were also evaluated under the same conditions, and this was shown by STD for comparison in each figure. FIG. 1 shows the relationship between the coat amount and the brightness. FIG. 2 shows the relationship between the residual brightness rate after a predetermined time and the coating amount. FIG.
Indicates the relationship between the coating amount and the carbon deposition amount. FIG.
The relationship between the remaining brightness rate and the lighting time is shown with the coat amount as a parameter.

As shown in FIG. 1, the initial brightness decreases as the coating amount increases. The STD having a coat of 0 has the highest brightness, but the relative brightness of the product of the present invention having a coat amount of about 5000 μg / g is about 50% when the STD is 100%, which is sufficient in consideration of the life described later. Withstand practical use.

As shown in FIG. 2, the residual brightness ratio, which is the life, increases as the coating amount increases. STD with 0 coat
Has a relative residual brightness of 20%. 50 coats
The relative luminance of the product of the present invention of about 0 μg / g is 70% or more, which is 3 times or more of STD.

Each sample was surface analyzed after a life test. As shown in FIG. 3 showing the result, the carbon deposition amount decreases as the coating amount increases. In the STD having a coat of 0, the relative amount of attached carbon is about 3. Coat amount is 500μ
The relative amount of carbon deposited on the product of the present invention of about g / g is about 1.5, and the amount of attached carbon of the product of the present invention on the coating amount of about 5000 μg / g is about 1 in relative value.
It is about one-third of that.

As shown in FIG. 4, the residual brightness ratio decreases as the lighting time increases, but the decreasing ratio of the residual brightness ratio with the increase in the lighting time decreases as the coating amount increases. In short, as the amount of coat increases, the luminance is less likely to decrease. For STD with 0 coat, lighting time is 1
When it exceeds 000 hours, the residual brightness rate drops to about 25% of the initial brightness, but in the case of the product of the present invention having a coating amount of about 800 μg / g, about 80% of the initial brightness is maintained.

As shown by the above data, the coat amount is 5
There is no practical problem if it is in the range of 00 μg / g to 5000 μg / g. In addition, 800 μg / g to 2000 μg / g
Within the range, the most preferable effect is obtained.

(2) Example 2 SrTiO ₃ : Pr activated with 0.0025 mol / mol of Pr and added with 0.2 mol / mol of Al,
An Al phosphor is prepared. RuO _2-x is added to the phosphor 40
Coat with 00 μg / g. This phosphor was mounted on a fluorescent display tube and subjected to tests such as initial luminance and life test under the same conditions as in Example 1. For comparison, the same test was performed on STD.

The phosphor of the sample of this example had an initial luminance of 80% as compared with STD. For life characteristics, see STD
Is 20%, while the phosphor of the sample of this example shows a good value of about 90%.

In each of the embodiments described above, SrTi
The O ₃ : Pr, Al phosphor was coated with PtO _2−x (0 ≦ x <2) or RuO _2−x (0 ≦ x <1). Regarding the phosphor, not only SrTiO ₃ : Pr, Al phosphor but also SrTiO ₃ : Pr, Al phosphor
rTiO ₃ : Pr fluorescent substance other than Al, such as Ga
Even if In, In, or the like is added, the same effect as that in the above-described embodiment can be obtained by coating the above-mentioned substance.

[0027]

According to the present invention, it is possible to provide a phosphor containing SrTiO ₃ which does not contain Cd, emits light from a low voltage, and has good life characteristics.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the coating amount of a substance having an oxidizing action and the brightness of a phosphor.

FIG. 2 is a graph showing the relationship between the residual brightness of a phosphor after a predetermined time has elapsed and the coating amount of a substance having an oxidizing action.

FIG. 3 is a graph showing the relationship between the coating amount of a substance having an oxidizing action and the amount of carbon attached to a phosphor.

FIG. 4 is a graph showing the relationship between the remaining brightness rate of the phosphor and the lighting time, using the coating amount of a substance having an oxidizing action as a parameter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Sato 629 Oshiba, Mobara-shi, Chiba Futaba Electronics Co., Ltd.

Claims (4)

[Claims] 1. A phosphor comprising a phosphor having SrTiO ₃ as a matrix and a substance having an oxidizing action added thereto. 2. The substance having an oxidative action is PtO _2-x
The phosphor according to claim 1, which is an oxide containing at least one substance selected from (0 ≦ x <2) and RuO _2−x (0 ≦ x <1). 3. The phosphor according to claim 1, wherein the substance having an oxidative action covers the surface of the phosphor in either one of a film form and a fine particle form. 4. The energy gap of the phosphor is 5e.
The phosphor according to claim 1, which has a V or less.