JPS5913559B2 - Fluorescent material for slow electron beam excitation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a phosphor suitable for an electron tube excited by a slow electron beam, such as a fluorescent display tube.

Conventionally, self-activating phosphors mainly composed of zinc oxide have been used under applied voltages of several KV or more on short-afterglow phosphor surfaces such as cathode ray tubes for fly flea spot scanners. It is known that it emits light even when excited with an electron beam of about several eV (H, W. Level 2; In
production to Lumine-sence
ofSolids, 1949, P156, P427, etc.), and in recent years it has also been applied to low-speed electron beam excitation light emission such as fluorescent surfaces for fluorescent display tubes. Incidentally, the fluorescence efficiency of a self-activating phosphor containing zinc oxide as a main component by electron beam excitation is reported to be 7.5% when used in a common cathode ray tube for fly fern spot scanners. (A. 15 Bril & A, Klassens, Ph
ilipsRes, Repts.

7P401 (1952)) when excited with a low-velocity electron beam of about 20 to 30 eV, such as from a fluorescent display tube, the luminous efficiency was 1.3 to 2.0%.
This is significantly lower than when excited by an electron beam accelerated at a high voltage.

Therefore, when this phosphor is used in fluorescent display tubes that are excited by low-speed electron beams, it consumes a lot of power, especially a large current, which places a heavy burden on the cathode.
It had disadvantages such as having an adverse effect on lifespan and other problems. In addition, the luminous efficiency and acceleration of excited electrons of a conventional self-activating phosphor whose main component is zinc oxide (this one contains 3 pμm of cadmium, 25 ppm of copper, and 15 pμm of silver as impurities by weight) Figure 1 shows the voltage relationship. 30 The present invention aims to eliminate the above-mentioned drawbacks by providing a phosphor that exhibits a higher luminous efficiency than conventional ones by excitation with a slow electron beam.

That is, the present invention provides a self-activated zinc oxide phosphor for excitation with slow electron beams, characterized in that metal impurities, particularly cadmium, contained in the phosphor are reduced to 1 pμm or less. The term also includes phosphors for excitation with slow electron beams which contain 10 ppm or less of other metal impurities, particularly copper and silver.

It has long been known that certain impurity elements have a detrimental effect on the luminescence of phosphors, and in particular, when they have the effect of reducing luminous efficiency, they are treated as killer elements.
), but Kiraichi is a phosphor whose effects do not change even if the usage conditions of the phosphor are changed, for example, the acceleration voltage of excited electrons, and it is uniformly harmful. It is believed that there is.

However, as a result of various studies aimed at improving the luminous efficiency of the phosphor, certain metal impurities contained in the phosphor related to the present invention have not been adopted in cathode ray tubes for flying spot scanners, etc. When excited by an electron beam accelerated at a relatively high voltage such as
It has been found that only slow electron excitation below V has a detrimental effect on the luminescence of the phosphor.

As detailed below, certain metallic impurity elements such as cadmium, copper, and silver have a significant effect on the luminous efficiency of self-activated zinc oxide phosphors, especially for slow electron beam excitation. Although the reason for this has not yet been fully elucidated, it is probably because as the penetration depth of electrons into the phosphor particles becomes shallower, surface levels created by impurities and contamination greatly contribute to the luminous efficiency. This is thought to be the cause of this decline. The present inventors have completed the present invention by paying attention to this recognition. In other words, we have found an effect in a specific range of impurities that are inevitably mixed in as raw materials for phosphors or in the phosphor manufacturing process.

The details are described below. Table 1 shows the results of the luminous efficiency when phosphors were created by adding various impurities using conventional raw materials for phosphors. Among the metal impurities that exert an effect, cadmium has the most significant effect, followed by copper and silver.

Regarding the other impurities listed in the table, addition of a few plus ppm shows almost no harmful effect. Furthermore, the luminous efficiency when excited at high voltage shows a value that is not significantly different for any impurity.

Note that Table 1 excludes nickel iron, lead, and other heavy metals that exhibit a sparkling effect even at high voltages. Next, we examine in detail the effect of metal impurities such as cadmium, which has a particularly strong effect on low-voltage excitation, using particularly purified raw materials. As shown in Figure 2, we find that the lower the content, the lower the voltage. The luminous efficiency tends to increase with excitation. Furthermore, in the same figure, in the case of high voltage excitation, the luminous efficiency does not change much even if the content of impurities changes. Further, in low voltage excitation, the luminous efficiency improves at a few ppm for copper and silver, particularly at 10 ppm or less, and for cadmium at a few ppm, especially at 1 ppm or less. Furthermore, the luminous efficiency when these impurities coexist is shown in Table 2 together with the conventional example, and the one with a small content of cadmium, copper, and silver shows the highest efficiency with low oni pressure excitation. ing. Examining the contents of Table 2 in more detail, we find that the most effective way to significantly improve luminous efficiency with slow electron excitation compared to conventional methods is by reducing cadmium, and that copper and silver are more effective than cadmium. It can be seen that although the effect is not large, it still has the effect of improving the luminous efficiency several times over the conventional one. The relationship between luminous efficiency and excitation voltage for Sample Blacks 1 to 6 listed in Table 2 is as shown in FIG. 3, and the lower the metal impurity content, the higher the luminous efficiency under low voltage excitation.

Further, the relationship between the luminous efficiency and the excitation voltage for Sample Black 7 is the same as that shown in FIG. 1 previously shown, but is also shown in FIG. 3. Third
The curve numbers in the figure correspond to the sample numbers in Table 2. As shown in FIG. 3, the luminous efficiency of a device with a low impurity content becomes higher than that of a conventional device or a device with a high impurity content at a low voltage of about 1000 eV or less. The present invention will be specifically explained below using examples.

Example 1 Powder whose main component is zinc oxide, which is a raw material, is
Dissolved in 0% by weight sulfuric acid solution, then passed through hydrogen sulfide,
Generates zinc sulfide.

The zinc sulfide that is initially formed and precipitated contains many impurity elements, so if this is removed once and all the rest is precipitated as zinc sulfide, the total amount of impurities will be approximately 10-5.
% or less of zinc sulfide powder is obtained.
This zinc sulfide powder is heated at 7000C to 1000C for several to 10 hours in a stream of high-purity oxygen from which dust has been removed through a filter to completely convert it into zinc oxide. The zinc oxide thus obtained has a significantly higher purity than zinc oxide that is normally available industrially, and also has a perfect matrix composition. This was heated at 95% in a nitrogen stream containing 25% hydrogen.
A self-activated zinc oxide phosphor was obtained by firing at 0° C. for 30 minutes. This product has the purity shown in Table 2, sample shop 1, and has a luminous efficiency of about 3 compared to conventional products under low voltage excitation.
It has improved twice as much. Using this phosphor, a phosphor film having a thickness of about 50 μm was formed on a substrate by a precipitation method to prepare a phosphor display tube. In this case, at an applied voltage of 25 V, the optical output was about 2.7 times that of the conventional one. Example 2 Metallic zinc refined by electrolysis was heated to 700°C in a high-purity oxygen stream from which dust was removed using a filter, and burned to obtain high-purity zinc oxide powder, which was mixed with 5% hydrogen and 95% nitrogen. % mixed gas flow at 850° C. for 1.5 hours to obtain a self-activated zinc oxide phosphor.

This product has the purity shown in Table 2, Sample 2, and its luminous efficiency is about 2.5 times higher than that of the conventional product under low voltage excitation. As in Example 1, a fluorescent display tube was made using the phosphor of this example, and the fluorescent display tube had a voltage of 25V.
The optical output was about 2.3 times that of the conventional one under an applied voltage of . Example 3 No. 1 zinc white, which is industrially produced as a pigment, was calcined in air at 1100°C for 5 hours to mainly reduce the cadmium content by evaporation, and after cooling, the average particle size was reduced using a pole mill. 1.5~2.5μ
Grind well until fine.

This material was heated to 800℃2 in a nitrogen stream containing 4% hydrogen.
After time baking, a self-activated zinc oxide phosphor is obtained. The purity of this product is 0.7 ppm cadmium and 7.5 ppm copper.
The pm silver was 10 ppm, and the luminous efficiency was 3.5% at 25 eV excitation and 7.401 at 10 KeV excitation. That is, at low voltage excitation (25 eV), the luminous efficiency was improved by approximately twice that of the conventional one. Further, as in Example 1, when a fluorescent display tube was prepared using the phosphor of this example, it exhibited a luminous efficiency approximately 1.9 times higher than that of the conventional one at 25 eV excitation. As described above, the phosphor of the present invention has a significantly higher luminous efficiency than the conventional one when excited by low-speed electrons of about 1000 eV or less, which is useful for reducing the power consumption and service life of fluorescent display tubes in practice. It has various advantages such as being able to extend the In addition,
The present invention does not include any lower limit for the content of cadmium, copper or silver.

This is because it is currently impossible to produce a self-activated zinc sulfide phosphor that does not contain any impurities such as cadmium, copper, or silver, and the actual state of its effects is unknown. The amount of impurities can only be detected down to about 0.1 ppm using current ordinary analytical techniques, so experimental data could only be obtained up to 0.1 ppm. However, if analytical techniques improve in the future, the lower limit of the impurities mentioned above will exceed O. It is expected from FIG. 2 that sufficient effects will be exhibited even in the range of 0.1 ppm. Furthermore, although the phosphor of the present invention has mainly been described as a fluorescent display tube, it can also be used in various cathode ray tubes that use electron beams applied at low voltage, and the present invention is applicable to fluorescent display tubes. It is not limited to the use of

[Brief explanation of the drawing]

Figure 1 shows the relationship between acceleration voltage of excited electrons and luminous efficiency in a conventional self-activated zinc oxide phosphor, and Figure 2 shows the relationship between impurity content and luminous efficiency in various phosphors including the phosphor of the present invention. The efficiency relationship is shown for 10KeV and 25e ribs.

Claims (1)

[Claims] 1. In a self-activated zinc oxide phosphor, a weight ratio of 1 ppm or less (
A phosphor for low-speed electron beam excitation, characterized in that it contains cadmium (excluding 0). 2 In the self-activated zinc oxide phosphor, the weight ratio is 1 ppm or less (
A phosphor for excitation with a slow electron beam, characterized in that it contains cadmium (excluding 0) and copper at a weight ratio of 10 ppm or less (excluding 0). 3 Weight ratio of 1 ppm or less in self-activated zinc oxide phosphor (
A phosphor for excitation with a slow electron beam, characterized in that it contains cadmium (excluding zero) and silver at a weight ratio of 10 ppm or less (excluding zero). 4 1 ppm or less by weight in self-activated zinc oxide phosphor (
A phosphor for excitation with a slow electron beam, characterized in that it contains cadmium (excluding zero) and copper and silver at a weight ratio of 10 ppm or less (excluding zero).