JP2956123B2 - Green phosphor for color cathode ray tubes - Google Patents

Description

The present invention relates to a green phosphor for a color cathode ray tube in a color display device such as a color TV, particularly a high-brightness TV.

[Summary of the Invention]

The present invention relates to a green phosphor for a color cathode-ray tube comprising ZnS: Cu, Al, wherein the activator Cu has a content of 7.5 × 10 ^{−4 to} 1.5 × 10 ⁻³ mol / mol.
By being selected as mol ZnS, the ratio [Cu] / [Al] (molar ratio) of having a crystal having a hexagonal structure to Al of each activator Cu is set to 1 to 1/10, An object of the present invention is to improve the linearity of a current-brightness characteristic in a high current region, and to provide a phosphor that is resistant to high electron beam excitation.

[Conventional technology]

In recent years, the brightness of projectors, ie, projection type TVs (televisions), high-definition color CRTs (cathode ray tubes),
Improvement of the luminance characteristics with the spread of V is an issue. For example, for large color TVs, an electron gun with an impregnated cathode compatible with high excitation has been developed, and its spot diameter has been reduced, that is, the current per unit area has been increased, and high-definition color CRTs have also been developed. An electron gun has been improved in which the spot diameter is reduced along with the reduction in the pixel pitch. For this reason, there is a demand for a luminance characteristic in which luminance maintains linearity even with a high current, and a longer life at such a high current, that is, a high luminance.

In such a color cathode ray tube, red, blue and green phosphors are used as the three primary colors of the image. For example, in Japanese Patent Application Laid-Open No. 63-150372 (Document 1), a projection type TV or the like as described above is used. A blue phosphor having good luminance characteristics, that is, capable of emitting light for a sufficiently long time even at a high current and a high luminance has been proposed.

As the green phosphor, zinc sulfide ZnS: Cu, Al to which an activator such as Cu, Al or the like is added is generally used. For such a green phosphor, Japanese Journal of Applied Physics ( Japanese Journal of Ap
plied Physics) Vol.13, No.10, October, 1974 (Reference 2)
In this report, there is a report on a change in emission intensity with respect to a change in each concentration of activators Cu and Al at a constant current value. However, no consideration or improvement has been made on the luminance characteristics under a high current as described above.

On the other hand, shortening the life of the green phosphor ZnS: Cu, Al has also become a problem due to the deterioration due to excitation under such high current, and in particular, the deterioration of the linearity of the current-luminance characteristics of the green phosphor, namely saturation. There is also a problem that so-called magenta ring easily occurs due to the occurrence of the characteristic.

[Problems to be solved by the invention]

The present invention aims to improve the current-luminance characteristics of the green phosphor made of ZnS: Cu, Al as described above.

[Means for solving the problem]

The present invention relates to a green phosphor for a color cathode-ray tube comprising ZnS: Cu, Al, wherein the activator Cu has a content of 7.5 × 10 ^{−4 to} 1.5 × 10 ⁻³ mol / mol.
Selected as mol ZnS, ratio of each activator Cu to Al [Cu]
/ [Al] (molar ratio) is from 1 to 1/10, and has crystals of a hexagonal structure.

[Action]

Excitation current density (I _k ) under electron beam excitation when using the above-described green phosphor for a color cathode ray tube according to the present invention.
FIG. 1 shows the luminance (B) characteristics.

In FIG. 1, line a shows the characteristics of the green phosphor for a color cathode ray tube according to the present invention, and line b shows the characteristics of the conventional green phosphor for a color cathode ray tube. As can be seen from FIG. 1, in the case of the present invention, the luminance is maintained linear even at a high current value as compared with the conventional green phosphor.
And the like, it is possible to increase the brightness.

This is because the activator Cu of the green phosphor composed of ZnS: Cu, Al is used.
By selecting at least 7.5 × 10 ^-4 mol / mol ZnS, the concentration of each activator Cu, Al becomes larger than before, and the luminescence center by this activator increases even at high current, It seems that the linearity in the current-luminance characteristics can be improved. However, in this case, if the concentration of Cu is set to 1.5 × 10 ⁻³ mol / mol ZnS or more, Cu that is not substituted by Zn enters into the interstitial space, and the energy level changes and the like, so that the emission intensity decreases. In the present invention, the activator Cu is used in an amount of 7.5 × 10 ^{−4 to} 1.5 × 10 ⁻³ mol / mol ZnS.
There is a reason to choose.

In the present invention, the ratio of each activator Cu to Al [C
u] / [Al] (molar ratio) was set to 1 to 1/10, but this relevance was confirmed by the activator C in ZnS described in the above-mentioned document 2 shown in FIG.
It can be understood by observing the change in emission intensity when the concentrations of u and Al are changed. In FIG. 2, the solid line c represents Cu.
When the molar ratio [Cu] / [Al] to Al is fixed to 1/2 and the concentrations of Cu and Al are changed, the chain line d indicates that the concentration of Cu is 1.5.
× 10 ^-4 mol / mol fixedly to ZnS case of changing the concentration of Al, where the dashed line e is obtained by changing the concentration of Cu by fixing the concentration of Al in 3 × 10 ^-4 mol / mol ZnS Show. As can be seen from FIG. 2, the molar ratio of Cu to Al [Cu] / [Al] is 1 /
When fixed to 2, the light emission intensity becomes almost constant as shown by the line c. On the other hand, the molar ratio of Cu to Al [Cu] /
[Al] is greater than 1, that is, the concentration of Al is 1.
The emission intensity is remarkably reduced when the concentration is 5 × 10 ⁻⁴ mol / mol ZnS or less and when the concentration of Cu is 3 × 10 ⁻⁴ mol / mol ZnS or more in the line e, and the molar ratio of Cu to Al is reduced. [Cu]
It can be seen that / [Al] should be 1 or less.

Note that this ratio [Cu] / [Al] is less than 1/10,
If it exceeds 10 times, the crystal structure of ZnS is affected, so that the emission intensity is reduced.

Therefore, by setting the ratio [Cu] / [Al] of each activator Cu to Al to 1 to 1/10, good emission intensity can be obtained,
By selecting the concentrations and concentration ratios of these activators, the luminance characteristics at high current can be improved.

〔Example〕

Hereinafter, examples of the green phosphor for a color cathode ray tube according to the present invention will be described in detail. In each case, a green phosphor was synthesized by the following method.

First, commercially available high-purity (luminescence grade) zinc sulfide Zn
S, 99.99% copper sulfate CuSO ₄ and aluminum sulfate Al ₂ (S
O ₄ ) ₃ is weighed at a predetermined ratio to obtain an aqueous solution, a predetermined amount of magnesium chloride MgCl ₂ is further added, and the mixture is dried by a rotary evaporator.

Next, 10% by weight of 99.999% sulfur S is added to the prepared raw material, and the mixture is filled in a quartz or alumina crucible. The inner lid is covered with 25% by weight of granular activated carbon, and the outer lid is placed thereon.

The firing is performed at a temperature of 200 ° C./hour to a predetermined temperature, and is held for a predetermined time, in this case, 4 hours in each case. After this firing,
Take out of the furnace and wash with warm water sufficiently to remove residual MgCl ₂ .

Examples, reference examples, and comparative examples performed by the above-described method are shown below.

Reference Example 1 1 mol of ZnS, 7.5 × 10 ⁻⁴ mol of CuSO ₄ and Al ₂ (SO ₄ ) ₃ ,
MgCl ₂ was synthesized at 1 × 10 ⁻³ mol and the firing temperature was 900 ° C.

Reference Example 2 1 mol of ZnS, 1.5 × 10 ⁻³ mol of CuSO ₄ and Al ₂ (SO ₄ ) ₃ ,
MgCl ₂ was synthesized at 1 × 10 ⁻³ mol and the firing temperature was 900 ° C.

Example 1 mol of ZnS, 7.5 × 10 ⁻⁴ mol of CuSO ₄ and Al ₂ (SO ₄ ) ₃ ,
MgCl ₂ was added at 1 × 10 ⁻³ mol, ZnSe (zinc selenide) was further added at 0.03 mol / mol ZnS, that is, 0.03 mol in this case, and the sintering temperature was set at 1200 ° C.

Comparative Example 1 1 mol of ZnS, 1.5 × 10 ⁻⁴ mol of CuSO ₄ and Al ₂ (SO ₄ ) ₃ ,
MgCl ₂ was synthesized at 1 × 10 ⁻³ mol and the firing temperature was 900 ° C.

In order to evaluate the characteristics of each phosphor thus synthesized, the excitation current density was changed to 0.4 × 40 μA / cm ² as a measure of the saturation degree of the luminance with respect to the excitation current density as shown in FIG. The inclination of the luminance at that time was defined as a γ value, and the γ value in Comparative Example 1 was set as 1, for relative evaluation. Table 1 shows the results.

The phosphor of Comparative Example 1 has the same composition as ZnS: Cu, Al used in a conventional color TV commercial product, and has the same emission characteristics as the conventional color TV commercial green phosphor.

As can be seen from Table 1, the γ value of the phosphor according to Reference Example 1 was improved by 8% with respect to the conventional emission characteristics. 15% for the phosphor according to Reference Example 2, and 18% for the phosphor according to Example 3.
% Also improved the γ value.

In the examples, since the phosphor was synthesized at a firing temperature of 1200 ° C., the crystal structure becomes hexagonal. Table 2 shows the results of measuring the forced deterioration rate of the phosphor according to Reference Example 1 and the phosphor according to Example 3. Here, the measurement of the forced deterioration rate was performed with the excitation current density set to 500 μA / cm ² respectively.
After energizing for 1000 hours, cool for 1 day, and increase the excitation current density to 250
μA / cm ^2, and the change (deterioration) of the emission intensity was measured.

As can be seen from Table 2, the cubic phosphor according to Reference Example 1 has a reduction rate of 38% from the initial luminance, whereas the hexagonal phosphor according to the embodiment has a reduction of only 15%. Without
It can be seen that the crystallinity is remarkably stabilized and the life is prolonged.

When the crystal structure of the green phosphor becomes hexagonal, the emission spectrum shifts to the shorter wavelength side by about 140 °, so that ZnSe, CdS, and ZnSe having a small band gap are 2 to 2.
It is necessary to adjust the chromaticity by adding 5 mol% or by adding Au (gold) in addition to Cu and Al.
In Examples, a good green spectrum could be obtained by adding 3 mol% of ZnSe to synthesize a phosphor.

In each of the embodiments described above, the ratio [Cu] / [Al] of the activator Cu to Al was set to 1/2, but this ratio may be between 1 and 1/10 described above. As described above, various changes can be made such as changing the firing temperature and adding an additive.

〔The invention's effect〕

As described above, the green phosphor for a color cathode-ray tube made of ZnS: Cu, Al according to the present invention has an activator Cu of 7.5 × 10 ^{-4 to} 1.5.
× 10 ⁻³ mol / mol ZnS, and the current-brightness characteristics, especially high, were obtained by setting the ratio [Cu] / [Al] (molar ratio) of each activator Cu to Al to 1 to 1/10. The characteristic in the current region, that is, the linearity can be improved.
As shown by the line a in the figure, a phosphor with good electron beam excitation can be obtained.

Further, for example, in the above-described phosphor having good electron beam excitation, the sintering temperature is increased to make the crystal structure hexagonal, and ZnSe is added to avoid a shift in the emission spectrum. A long-life green phosphor can be obtained.

[Brief description of the drawings]

FIG. 1 shows an excitation current density (I _k ) under electron beam excitation when a green phosphor for a color cathode ray tube according to the present invention is used.
FIG. 2 is a diagram showing a luminance (B) characteristic, and FIG. 2 is a diagram showing a change in emission intensity when the concentrations of activators Cu and Al in ZnS of the green phosphor for a color cathode ray tube are changed.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-110781 (JP, A) JP-A-56-112050 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09K 11/56

Claims (2)

(57) [Claims] 1. A green phosphor for a color cathode ray tube comprising ZnS: Cu, Al, wherein an activator Cu is selected to be 7.5 × 10 ^{−4 to} 1.5 × 10 ⁻³ mol / mol ZnS, and each activator Cu A green phosphor for a color cathode ray tube, characterized in that the ratio [Cu] / [Al] (molar ratio) to Al is from 1 to 1/10 and the crystal has a hexagonal structure. 2. The method according to claim 1, wherein ZnSe is contained.
The green phosphor for a color cathode ray tube according to the above.