JPH11349937A - Blue-emitting phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blue-emitting phosphor having excellent electric current characteristics and scarcely deteriorating brightness. SOLUTION: A phosphor for color cathode ray tubes has the following requirements. (1) The phosphor is expressed by the formula: ZnS: Ag, M, Al. (2) The M in the formula is one or two of Cu and Au. (3) The content of the Ag is 200-50,000 ppm based on the phosphor. (4) The content of the Al is 50-1,500 ppm. (5) The crystal structure has a hexagonal system structure in an amount of >=50%. (6) The content of the M is 0.1-10 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blue light-emitting phosphor mainly used for a projection tube or a color cathode ray tube used at a high voltage and a high current, and particularly to Ag, one or both of Cu and Au. And improvement of a blue-emitting zinc sulfide phosphor activated with Al. More specifically, the present invention relates to a blue-emitting zinc sulfide phosphor having extremely excellent current characteristics and luminance degradation with respect to excitation energy.

[0002]

2. Description of the Related Art In recent years, color cathode ray tubes, display tubes, or projection tubes have been increasing in size and ultra-high definition, and accordingly, it has been required that phosphors have higher emission luminance. Therefore, the current density of the electron beam for exciting the phosphor is increased, and the phosphor is used in a high region. Therefore, the phosphor is required to have excellent current characteristics. Extremely good current characteristics are sometimes required for phosphors used in projection tubes.

[0003] The current characteristic is a characteristic that the emission luminance increases with an increase in the current density of an electron beam that stimulates the phosphor film. Phosphors having poor current characteristics do not have a linear increase in emission luminance in a high current density region. In other words, the emission luminance does not increase when the phosphor is strongly excited. In particular, since the phosphor for a projection tube is exposed to a high current density when used, luminance characteristics and current characteristics are emphasized.

The ZnS: Ag, Al phosphor conventionally used as a blue light-emitting phosphor does not satisfy the above requirements, and includes two crystal structures of a cubic system and a hexagonal system as an improvement measure. ZnS: Ag, Al have been developed (JP-A-62-95378). This phosphor uses zinc sulfide as a matrix and silver and aluminum as activators. The activation amount of silver and aluminum is 500 to 2000 ppm for silver and 250 to 1500 ppm for aluminum. This phosphor is
The hexagonal content is adjusted to the range of 0 to 12%.

Also, a zinc cadmium sulfide phosphor containing at least 50% of a hexagonal system has been developed (Japanese Patent No. 2561144).
In this phosphor, ZnS is partially replaced by CdS. The activation amount of silver and aluminum is 200 to 50,000 ppm for silver,
Aluminum is 100 to 50,000 ppm.

[0006] However, the blue light emitting phosphor described above has
It cannot be said that the phosphor is sufficiently satisfactory as a phosphor for a projection tube, and a phosphor having higher luminance and higher current characteristics is desired.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a blue light-emitting phosphor which has the above-mentioned problems with excellent luminance characteristics and current characteristics.

[0008]

Means for Solving the Problems The present inventors have proposed a high-temperature type zinc sulfide phosphor Z in which more than 50% of the crystal structure is hexagonal.
nS: As a result of conducting various studies on Ag-rich activated products in Ag and Al, by activating a specific amount of Cu or Au,
The inventors have found that the luminance is high and the current characteristics are improved, and the present invention has been completed.

The blue light-emitting phosphor of the present invention comprises the following:
Characterized by having the following configuration. That is, the general formula is represented by ZnS: Ag, M, Al. In this general formula, M is one or two elements of Cu and Au, and the content of Ag is 200 to the total amount of the phosphor. The content of Al is in the range of 50-1500 ppm, the crystal structure is at least 50% hexagonal, and the content of M is in the range of 0.1-10 ppm. .

The blue light-emitting phosphor of the present invention exerts its effect if at least 50% of the ZnS crystal structure of the base material is hexagonal. This is preferable because the effect is increased.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a zinc sulfide phosphor ZnS: Ag, Al in which 50% or more of the crystal structure is occupied by a large amount of Ag, and a small amount of Cu, Au, or a mixture of Cu and Au.
By activating, it is possible to obtain a blue light emitting phosphor having good current characteristics.

Conventionally, a zinc sulfide phosphor ZnS: Ag, Al has been used as a blue light-emitting phosphor used for a CRT or the like, and a large amount of Ag has been activated in order to improve its current characteristics. . Also in the present invention, activator Ag and coactivator Al are basically activated in large amounts. Specifically, a general color cathode ray tube has an Ag content of about 200 ppm, but in a phosphor for a projection tube excited in a high current region, at least 300 ppm of the Ag content is activated, and the The characteristics are good. A in the phosphor of the above general formula
The content of g is preferably in the range of 200 to 50,000 ppm, and more preferably in the range of 280 to 1500 ppm. The content of Al is preferably in the range of 50 to 1500 ppm.

The reason is that if the content of Ag is 200 ppm or less and 50,000 ppm or more, its effectiveness is low, and if the content of Al is also 50 ppm or less and 1500 ppm or more, its effectiveness is low.

It is generally said that zinc sulfide has a cubic or hexagonal crystal structure or a mixed crystal structure depending on the firing temperature.
Transforms from cubic to hexagonal in a very narrow temperature range around 1030 ° C. In the zinc sulfide phosphor of the present invention, the proportion of the hexagonal system in the crystal structure is preferably 50% or more,
It is more preferably at least 80%, and this ratio can be changed by controlling the firing temperature.

FIG. 1 shows relative current characteristic values with respect to current density when Cu is activated at 5 ppm. The relative current characteristic value used in this specification is obtained as follows. First, a current characteristic value is obtained for each phosphor. Here, the current characteristic value is an acceleration voltage of the electron gun of 27 kV,
The luminance Y ₅₀ (%) when the current density is 50μA / cm ^2, a value obtained by dividing the luminance Y ₅ (%) when the current density is 5 .mu.A / cm ^2. The value obtained by dividing the current characteristic value thus obtained by the current characteristic value of the hexagonal zinc sulfide phosphor (without Cu and Au) as the reference phosphor is the relative current characteristic value. The relative current characteristic value = 1 in FIG. 1 is a reference phosphor.

When the current density is changed from 5 μA / cm ² to 50 μA / cm ² , an ideal phosphor whose emission luminance increases linearly has a current characteristic value of 10. Actual phosphors do not increase linearly with the change in current density, and luminance saturation occurs at 50 μA / cm ² or less.
The current characteristic value is a numerical value of 10 or less. Here, the relative current characteristic value is a relative value with respect to the current characteristic value of the reference phosphor, so that the relative current characteristic value larger than 1 is a phosphor that is superior to the reference phosphor.

The curve a in FIG. 1 shows the relative current characteristic value of the zinc sulfide phosphor of the present invention which is 100% hexagonal, and the curve b shows the relative current characteristic value of the conventional zinc sulfide phosphor which is 100% cubic. . As is clear from this figure, the conventional cubic system 100%
It can be understood that the current characteristics are not improved by activating Cu, but the current characteristics of the 100% hexagonal zinc sulfide of the present invention are improved by activating Cu.

FIG. 2 shows relative current characteristic values with respect to the content of the hexagonal system. Current density 50 of Fig. 1
The relative current characteristic values when the ratio between the hexagonal system and the cubic system is changed under the condition of μA / cm ² are shown.

As is clear from the curve c in FIG. 2, the zinc sulfide phosphor of the present invention has an increased relative current characteristic value with an increase in the content of the hexagonal system. Then, when the content of the hexagonal system exceeds about 50%, the relative current characteristic value exceeds 1, indicating that the effect is exhibited. Further, it can be seen that when all the components are hexagonal, the effect is remarkably improved.

In this specification, the content (%) of the hexagonal system is a value calculated by the following equation in an X-ray diffraction diagram.

H (%) = 1.69B / (A + 0.69B)

Wherein H is the content of hexagonal ZnS,
A: height of the diffraction line where hexagonal and cubic ZnS overlap, B: height of the hexagonal diffraction line of 2Q = 51.7 ′)

The above equation is derived from the following WA Steward equation.

R = B / A = H / 1.69-0.69H

The above general formula ZnS: Ag, M, Al
(Where M is one or two elements of Cu and Au), the content of Cu in the zinc sulfide phosphor of the present invention is in the range of 0.1 to 100 ppm with respect to the total amount of the phosphor. And more preferably in the range of 0.5 to 10 ppm. Also, the content of Au is 0.1 to 1 relative to the total amount of the phosphor similarly to Cu.
It is in the range of 0 ppm, and more preferably in the range of 0.5 to 10 ppm.

The reason is that if the content of Cu and Au is less than 0.1 ppm, its effectiveness is low, and if it exceeds 10 ppm, the color purity is deteriorated.

Further, the zinc sulfide phosphor of the present invention is characterized in that in addition to excellent current characteristics, luminance degradation is also excellent. FIG. 3 shows the forced deterioration characteristics. Curve d
Is a zinc sulfide phosphor of the present invention in which Cu is activated at 5 ppm, and a curve e is a conventional hexagonal zinc sulfide phosphor containing no Cu. The forced degradation characteristics were such that the phosphor film was excited at an acceleration voltage of 27 kV and the current density of the electron gun was 42 μA / cm ² , an extremely high current density as compared with the actual use state, and deteriorated in a short time. Forcible deterioration was performed for a certain period of time, and the luminance was measured before and after the forced deterioration test, and the change in luminance was compared. For the measurement of the luminance, the acceleration voltage of the phosphor was 27 kV, and the current density was 0.5 μA / cm ² . The brightness of the phosphor film before the forced deterioration test is set to 100%,
The luminance of the phosphor film after the forced deterioration test was measured, and the relative luminance was expressed as a percentage. In the forced deterioration test, a phosphor having no luminance reduction is a horizontal horizontal line whose relative emission luminance is always 100% in FIG. The more the phosphor deteriorates, the lower the curve becomes.

As is clear from the curve d in FIG. 3, the zinc sulfide phosphor of the present invention has less luminance degradation than the conventional phosphor.

[0029]

EXAMPLES The production method of the present invention will be described in detail with reference to Examples, but the following Examples are merely examples for embodying the present invention, and do not restrict the present invention.

The blue light emitting phosphor of the present invention can be manufactured by the method described below.

(Raw material preparation step) As phosphor raw material (A) ZnS (raw zinc sulfide powder) as raw material matrix (B) Ag, Cu, Au chloride, sulfate, nitrate (C) as activator As the activator, Al chloride, sulfate or nitrate is used, and if necessary, at least one of Cl, Br, I and F ammonium salts is used. (D) Sulfur powder, carbon powder or the like is used as an atmosphere regulator. (E) H ₃ BO ₃ , CeCO ₃ , Ti
O ₂ , P ₂ O ₅ , SiO ₂ , GeO ₂ or the like may be used.

(Raw material firing step) The above raw materials are kneaded in an optimum amount, dried at 100 to 110 ° C., and the obtained phosphor raw material mixture is filled in a heat-resistant container such as a quartz crucible or a quartz tube and fired. The calcination is performed in a sulfide atmosphere such as a hydrogen sulfide atmosphere, a sulfur vapor atmosphere, and a carbon dioxide atmosphere. Firing temperature is 1040-11
Adjusted to 00 ° C. The firing time varies depending on the firing temperature, the amount of the phosphor raw material mixture, and the like, but is adjusted between 1 and 8 hours.

(Post-treatment step) After firing, the obtained fired product is sufficiently washed with water, dried at 100 to 110 ° C, and sieved to obtain the phosphor of the present invention.

A specific example of the phosphor produced by the above steps will be described.

Example 1 Raw Material Preparation Step The following raw materials are prepared. Zinc sulfide raw powder ZnS 1000 g of copper sulfate CuSO ₄ 0.006 g of silver sulfate Ag ₂ SO ₄ 0.94 g of aluminum sulfate 18 water _{Al 2 (SO 4) 3 ·} 18H 2 O 1.85g potassium aluminum sulfate KAl (SO _{4) 2} 0.78g of ammonium chloride NH ₄ Cl 0.4 g Sulfur S 60 g The above raw materials are thoroughly mixed.

The mixed phosphor material is packed in a quartz crucible, placed in a furnace, and fired at a firing temperature of 1020 ° C. for 2 hours.

The fired product was taken out of the crucible, washed with water, and then sieved to obtain a zinc sulfide phosphor having a composition represented by ZnS: Ag, Cu, Al. The obtained zinc sulfide phosphor contained 630 ppm of Ag, 2.4 ppm of Cu, and 210 ppm of Al, and had a hexagonal system content of 50%.

Example 2 Raw Material Preparation Step The following raw materials are prepared. Zinc sulfide raw powder ZnS 1000 g of copper sulfate CuSO ₄ 0.006 g of silver sulfate Ag ₂ SO ₄ 0.94 g of aluminum sulfate 18 water _{Al 2 (SO 4) 3 ·} 18H 2 O 1.85g potassium aluminum sulfate KAl (SO _{4) 2} 0.78g of ammonium chloride NH ₄ Cl 0.4 g Sulfur S 60 g The above raw materials are thoroughly mixed.

The mixed phosphor material is packed in a quartz crucible, placed in a furnace, and fired at a firing temperature of 1080 ° C. for 2 hours.

The fired product was taken out of the crucible, washed with water, and sieved to obtain a zinc sulfide phosphor having a composition represented by ZnS: Ag, Cu, Al. The resulting zinc sulfide phosphor contained 640 ppm of Ag, 2.5 ppm of Cu, and 213 ppm of Al, and was 100% hexagonal.

Example 3 (Raw Material Preparation Step) The following raw materials are prepared. Zinc sulfide raw powder ZnS 1000 g of copper sulfate CuSO ₄ 0.013 g of silver sulfate Ag ₂ SO ₄ 0.94 g of aluminum sulfate 18 water _{Al 2 (SO 4) 3 ·} 18H 2 O 1.85g potassium aluminum sulfate KAl (SO _{4) 2} 0.78g of ammonium chloride NH ₄ Cl 0.4 g Sulfur S 60 g The above raw materials are thoroughly mixed.

The mixed phosphor material was packed in a quartz crucible, placed in a furnace, and fired at a firing temperature of 1080 ° C. for 2 hours. Thereafter, ZnS: Ag, Cu, Al was used in the same manner as in Example 2.
Thus, a zinc sulfide phosphor having a composition represented by the following formula was obtained. The obtained zinc sulfide phosphor was composed of 640 ppm of Ag, 5.2 ppm of Cu, and 208 pp of Al.
m, and the hexagonal system was 100%.

Example 4 (Raw Material Preparation Step) The following raw materials are prepared. Zinc sulfide raw powder ZnS 1000 g of copper sulfate CuSO ₄ 0.019 g of silver sulfate Ag ₂ SO ₄ 0.94 g of aluminum sulfate 18 water _{Al 2 (SO 4) 3 ·} 18H 2 O 1.85g potassium aluminum sulfate KAl (SO _{4) 2} 0.78g of ammonium chloride NH ₄ Cl 0.4 g Sulfur S 60 g The above raw materials are thoroughly mixed.

The mixed phosphor materials were packed in a quartz crucible, placed in a furnace, and fired at a firing temperature of 1080 ° C. for 2 hours. Thereafter, ZnS: Ag, Cu, Al was used in the same manner as in Example 2.
Thus, a zinc sulfide phosphor having a composition represented by the following formula was obtained. The obtained zinc sulfide phosphor has 640 ppm of Ag, 7.5 ppm of Cu, and 209 pp of Al.
m, and the hexagonal system was 100%.

Example 5 Raw Material Preparation Step The following raw materials are prepared. Zinc sulfide raw powder ZnS 1000 g of copper sulfate CuSO ₄ 0.013 g of chloroauric AuCl ₃ 0.018 g silver sulfate Ag ₂ SO ₄ 0.89 g of aluminum sulfate 18 water _{Al 2 (SO 4) 3 ·} 18H 2 O 1.85g potassium aluminum sulfate KAl (SO _{4 2} ) 0.78 g Ammonium chloride NH ₄ Cl 0.4 g Sulfur S 60 g Mix the above raw materials thoroughly.

The mixed phosphor materials were packed in a quartz crucible, placed in a furnace, and fired at a firing temperature of 1080 ° C. for 2 hours. Thereafter, ZnS: Ag, Cu, A was used in the same manner as in Example 2.
A zinc sulfide phosphor having a composition represented by u, Al was obtained. The obtained zinc sulfide phosphor was composed of 600 ppm of Ag, 5.0 ppm of Cu,
And Al at 196 ppm, and the hexagonal system was 100%.

Comparative Example 1 Raw Material Preparation Step The following raw materials are prepared. Zinc sulfide raw powder ZnS 1000 g silver sulfate Ag ₂ SO ₄ 0.94 g of aluminum sulfate 18 water _{Al 2 (SO 4) 3 ·} 18H 2 O 1.85g potassium aluminum sulfate KAl (SO _{4) 2} 0.78g of ammonium chloride NH ₄ Cl 0.4 g of sulfur S 60g The above ingredients are mixed well.

The mixed phosphor material was packed in a quartz crucible, placed in a furnace, and fired at a firing temperature of 1080 ° C. for 2 hours. Thereafter, ZnS: Ag, Al was used in the same manner as in Example 2. Thus, a zinc sulfide phosphor having the following composition was obtained. The resulting zinc sulfide phosphor contained 640 ppm of Ag and 218 ppm of Al, and was 100% hexagonal.

Table 1 shows the evaluation results of the light emission characteristics of these examples and the conventional example.

[0050]

[Table 1]

[0051]

As described in the present invention, in the zinc sulfide phosphor ZnS: Ag, Al, a large amount of Ag-activated zinc sulfide phosphor in which the hexagonal system occupies 50% or more of the crystal structure is made of Cu, Au or Cu. By activating a small amount of Au and Au, the luminous properties were excellent, as compared with the conventional zinc sulfide phosphor, in that the relative current properties were excellent and the luminance degradation was small.

[Brief description of the drawings]

FIG. 1 shows relative current characteristics with respect to current density when Cu is activated at 5 ppm in each of a 100% hexagonal zinc sulfide phosphor of the present invention and a conventional 100% cubic zinc sulfide phosphor. Graph showing value relationships

FIG. 2 is a graph showing the relationship between the content of hexagonal system contained in the zinc sulfide phosphor of the present invention and the relative current characteristics.

FIG. 3 is a graph showing forced luminance degradation characteristics.

Claims (2)

[Claims] 1. A blue light-emitting phosphor having the following constitutions: The general formula is represented by ZnS: Ag, M, Al. In this general formula, M is one or two elements of Cu and Au, and the content of Ag is 200 to 50,000 ppm with respect to the total amount of the phosphor. Wherein the Al content is in the range of 50 to 1500 ppm, the crystal structure is at least 50% hexagonal, and the M content is in the range of 0.1 to 10 ppm. Phosphor. 2. The blue light emitting phosphor according to claim 1, wherein all of the crystal structures are hexagonal.