JPS6121580B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a blue-emitting phosphor suitable for color cathode ray tubes for display purposes, and an object of the present invention is to provide a material that has both practically good brightness and chromaticity characteristics as well as desirable afterglow properties. In recent years, display cathode ray tubes have been widely used for controlling and monitoring electronic computer terminals and blunt systems. In these cases, the display is in numbers, alphabets, katakana, kanji, or figures, and a color cathode ray tube is suitable because it has a large amount of functional information and is easy to read. However, since color cathode ray tubes for ordinary televisions mainly display continuously moving images, it is desired that the phosphors emitting each color have a short afterglow below the visual range.
On the other hand, the above-mentioned display cathode ray tubes often display characters or figures that are fixed for a certain period of time.
Therefore, by using a phosphor that exhibits appropriate afterglow, flickering of the screen can be reduced, making it easier to see, and it is also possible to reduce the number of pixels for image transmission. This has the advantage of reducing fatigue for the viewer and simplifying the rotation of the motion. Typical phosphors currently used for this purpose include green Zn ₂ SiO ₄ :Mn・As and red (Zn, Mg) ₃ (Po ₄ ) ₂ :Mn, the former being B ₁₀ %
(time for brightness to drop to 10% after stimulation stops) is 150m
sec, the latter has a sufficiently satisfactory performance of 120 msec. However, there are still no known substances in blue that have such afterglow properties, and it is a truly difficult problem to obtain a phosphor that also has good brightness and color tone characteristics. For example, it is commonly used
ZnS: Ag/Cl is good in terms of color tone and brightness, but the activator Ag has a metastable state at its energy level, like the activator Mn in the green and red emitting phosphors mentioned above. However, its B ₁₀ % is very short at 50 μsec, and the afterglow characteristics hardly change even if the matrix is treated or the structure is changed. In other words, ZnS kept at a high temperature of 1000℃ or more:
The Ag/Cl phosphor can be cooled by rapidly dropping it into cold water, which is called quenching, to create distortion in the crystal, or by holding it at 800 to 900°C for a long time to cool a part of the crystal. Attempts have been made to impart afterglow properties, such as by converting it into a cubic crystal form, but none of these methods have yielded the desired effect. On the other hand, ZnS:Cu.Cl, which emits green light, has a long afterglow property. This is due to the predominance of recombination type afterglow, which is often seen in photoconductive phosphors. Taking advantage of this property, we attempted dual activation of ZnS with both Ag and Cu. For charge compensation, Cl, which is effective in both cases, was added as a co-activator. In the case of Ag, the active weight is preferably the same as that normally used as a blue-emitting phosphor, and in the case of Cu, it is desirable that the chromaticity of blue light emitted by Ag does not deviate too much. The amount of Cl is set to approximately correspond to the total amount of Ag and Cu. The phosphor thus obtained emits a sufficiently satisfactory blue light during stimulation with cathode rays, and after the stimulation is stopped, it emits green light with a long afterglow time. In electron beam stimulation in a display cathode ray tube, beam scanning is repeated within a short period of time. Therefore, there is a strong contrast between the strong blue light emission during stimulation and the weak green afterglow when the beam passes, so there is almost no sensation of green. However, since green is a spectrum with high visibility, even a small amount of Cu is considered to be effective in reducing flicker. Examples will be described below. Example 1 100 g of ZnS (raw material powder), AgNO ₃ (as Ag) 0.04 〃 CuCl (as Cu) 0.00001 〃 NaCl 2.5 〃 BaCl ₂ 2.5 〃 Weigh the above and put it in an evaporation dish, add 70 ml of pure water, and mix well. Mix. After drying, this was filled into a quartz crucible, covered with a lid, and fired at 1200° C. for 1 hour in an electric furnace. The atmosphere inside the furnace is nitrogen. After cooling, take it out, wash it with warm water, and dry it. Example 2 ZnS: Ag.Cl phosphor 100 g CuCl (as Cu) 0.001 NH ₄ Cl 5 Weigh out the above, put it in an evaporation dish, add 50 ml of pure water, and mix well. After drying, it was transferred to a quartz crucible, covered, and fired in an electric furnace at 900°C for 1 hour. The inside of the furnace has a nitrogen atmosphere. After cooling, it was taken out, washed with warm water, and dried. The ZnS phosphor used as a raw material here was a commercially available blue-emitting phosphor used in color cathode ray tubes, and its Ag content was 0.037%. The crystals of the phosphors produced in Examples 1 and 2 were examined by X-ray diffraction, and it was confirmed that both were hexagonal crystals. It then emitted a bright blue color when stimulated with ultraviolet light and cathode rays. Here, the lower limit of the amount of Cu is 0.00001%, which is the amount below which the afterglow intensity is too weak and no reduction in flickering is observed, and the upper limit is 0.00001%, which is the amount that the addition of more than this will shift the blue light emission. The undesirable amount is 0.0001%. 0.01 of the amount of Ag
to 0.04% is the amount added that will provide sufficient blue light emission within this range. At the same time, Cl is introduced into the crystal from chloride added as a flux during firing, corresponding to the contained Ag and Cu. The firing temperature and time are not very strict, but if it is below 800°C, some cubic ZnS will be formed and the evolution characteristics will change.
If the temperature is 1,300°C or higher, crystal growth will be significant, resulting in a sintered state, resulting in decreased properties. A desirable temperature range is 900-1200°C. Incidentally, the firing time should be increased or decreased depending on the amount of the fired product. The characteristics of the phosphor obtained above were measured using a cathode ray tube. The results are shown in Table 1.

[Table] By limiting the amount of activator in the double-activated Ag and Cu ZnS phosphor, the deviation of the blue chromaticity point can be suppressed as much as possible to create a phosphor with the desired afterglow characteristics. I was able to get it. By combining this with the conventionally used green and red phosphors with long afterglow properties, it was possible to produce display cathode ray tubes with good color purity, well-balanced brightness, long afterglow properties, and low flicker. It became possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the emission spectrum distribution of the conventional phosphor a and the phosphor b of the present invention during cathode ray stimulation, and FIG. 2 is a diagram showing the afterglow attenuation characteristic of the phosphor of the present invention after the cathode ray stimulation is stopped.

Claims (1)

[Claims] 1 Hexagonal ZnS: In a double-activated phosphor in which Cu coexists with Ag and Cl, Ag is approximately 0.01 to 0.04
weight percent, Cu from approximately 0.00001
0.0001 weight percent dual activation with Ag and
A phosphor comprising Cl as a co-activator in an amount approximately corresponding to the combined chemical equivalent of Cu.