JPS5940178B2 - Method for producing europium activated stannic oxide phosphor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a europium-activated stannic oxide phosphor, and aims to provide a method that can more easily produce a bright phosphor.

It has already been found that a stannic oxide phosphor containing europium in a proportion of 1.times.10@-2 to 15 atom % begins to emit light at a very low threshold voltage of 5 V excitation voltage.

The emitted light color is reddish-orange with a spectral distribution as shown in FIG. Until now, ZnO:Zn phosphors have been used as phosphors for slow electron beams, but as is well known, their luminescent color is blue-green. This provides the possibility of multi-colored phosphors. Incidentally, in recent years, improvements to colorization of various display elements, such as light emitting diodes, fluorescent display tubes, liquid crystal elements, plasma display elements, and electromic display elements, have been commonly investigated.
This is essential for enriching the amount of displayed information and making the display easy to read.

Among these display elements, fluorescent display tubes in particular have features such as good visibility, high brightness, long life, a high degree of freedom in display patterns, and relatively low prices, making them useful for commercial purposes. It is widely used not only in commercial equipment but also in the field of consumer equipment, and it is thought that its range of applications will continue to expand in the future.

Considering this background, conventional blue-green emitting ZnO
: When red light emission is added to fluorescent display tubes that have only used Zn phosphors, the above-mentioned characteristics and complementary effects occur, increasing the practical value of fluorescent display tubes. It is clear that the price will rise. By the way, when actually manufacturing a SnO2:Eu phosphor, simply mixing the oxides of each component element mechanically and heat-treating it will not allow grain growth of sno2 and uniformity of Eu into the SnO2 matrix. It is quite difficult to achieve sufficient diffusion, so the applicant uses various devised coprecipitation methods, such as the oxalate coprecipitation method and the metastannate coprecipitation method. By improving the miscibility of Sn and Eu on the atomic scale,
It has been found that uniform diffusion during subsequent heat treatment is promoted, resulting in a brighter SnO2:Eu phosphor.

However, these methods require the Sn compound as a starting material to be soluble in an acidic solution, so the cost of the starting material is higher than that of an oxide. Moreover, it is quite difficult to produce a coprecipitated salt in which Sn and Eu are uniformly mixed, and it takes a long time, and the manufacturing cost is high. When uniformly mixing oxides or compounds that easily become oxides by thermal decomposition using a mechanical mixing method, cesium chloride is added to the raw materials as a fluxing agent to promote uniform diffusion of the components during heat treatment. In particular, the problems encountered in the above-mentioned methods are solved.

By the method of the present invention, it is possible to obtain a phosphor whose brightness is comparable to that obtained by coprecipitation. The method of the present invention will be described below with reference to Examples.

First, high-purity SnO2 powder with an average particle size of 0.1 μm was
U2O3 powder was added so that Eu was in a proportion of 1 atomic % based on the total amount of Sn and Eu.

Cesium chloride (CsCl) was added to the resulting mixture in weight percentages of 0.1%, 0.5%, 1%, based on the total amount.
3%, 7%, and 10% were added separately, and pure water was added to each and wet-mixed. For mixing, a polyethylene ball mill containing iron balls covered with urethane rubber was used to prevent contamination of impurities. The mixed powder obtained by drying each of the mixtures was placed in an alumina crucible, and heated to 0 at a temperature within the range of 1000 to 1600°C.
．． Heat treatment was carried out in air for 08 to 10 hours. Then, in order to remove the cesium chloride as a fluxing agent,
The heat-treated powder was poured into boiling pure water and stirred for about 30 minutes. The thus treated powder was filtered, thoroughly washed with water, and then dried to obtain a phosphor. Using the SnO2:Eu phosphor prepared as described above, Second
A low-speed electron beam emitting device as shown in the figure was constructed, and the brightness of the light emitted by each phosphor was investigated.

In FIG. 2, numeral 1 is a glass substrate, on one surface of which a transparent electrode 2 is formed, and furthermore, a fluorescent film 3 is coated on the soil.

The coating amount of the phosphor was 3 W/Cd. 4 is a mica board,
5x5m in the center! An opening having a size of L is provided, and the opening is positioned in front of the fluorescent film 3.
It is arranged parallel to the glass substrate 1.

A grid 5 has a honeycomb structure as shown in FIG. 3, and is arranged in front of and parallel to the mica plate 4.

6 is a thermionic radiation heater.

These components are enclosed within a vacuum glass container 7. In such a light emitting device, the grid voltage Ec
was set to 18V, and heater voltage Ef was set to 3V.

The anode voltage Eb was kept constant at 10, the fluorescent film 3 was excited, and the brightness of the light emitted by each phosphor was measured. Note that the excitation current density is constant at 1.5 mA/Cd. The results are summarized in the table below along with the manufacturing conditions. In the above table, Samples 1 to 6 show the effect of the amount of cesium chloride added.

As is clear from this, 0.1% by weight of cesium chloride
At this time, the brightness of the phosphor's light emission is 14 foot lamberts, which is almost the same value as in the case without additives. However, when the amount of cesium chloride was 0.5% by weight or more, a practical brightness of 257 lamberts or more was obtained, and when it was 3% by weight, it was still extremely bright. As the amount of cesium chloride increases, the brightness of the phosphor's emission decreases,
When it becomes 10% by weight, it becomes 23 foot lambert. From this, it is desirable that the amount of cesium chloride added be in the range of 0.5 to 7% by weight in order to obtain practical brightness (・o If the amount of cesium chloride added is large, the phosphor Grain growth becomes noticeable and the particle size increases.In the light-emitting device shown in Figure 2, the light emission is viewed from the electron beam irradiation surface, so in order to emit more excitation light, it is necessary to A fine phosphor with a large scattering of light is preferable.In general, grain growth increases the luminous efficiency of the phosphor, but if too much cesium chloride is added as a fluxing agent, the grain size becomes larger than necessary, and as described above, As the light scattering effect decreases, the brightness of the phosphor emission decreases.Incidentally, sample 3
The average particle size of the phosphor was about 1 μm, and that of sample 6 was about 12 μm. Adding too much cesium chloride as a flux will not only cause problems caused by grain growth as mentioned above, but also contamination of the phosphor by its component elements and impurities contained in cesium chloride. This is generally undesirable since it also increases the

Samples 7 to 10 and Sample 4 show the effect of heat treatment temperature. As is clear from these, if the heat treatment temperature is too low, the fluxing effect of cesium chloride will not be sufficiently exhibited, and therefore, it is practically desirable that the heat treatment temperature be 1100° C. or higher. However, if the temperature is too high, the grain growth of the phosphor becomes significant, and in sample 10, the average grain size reaches 12 μm, so it is desirable that the temperature be 1500° C. or lower. Samples 11 to 15 and Samples 16 to 19 each show the effect of heat treatment time. The former is the effect at the lower limit of the addition amount and temperature to obtain the fluxing agent effect, and
The latter shows their respective effects at their upper limits. As is clear from these results, in the former case, the heat treatment time of 5 minutes (0.08 hours) is too short, but in the latter case, the grains have grown to a satisfactory extent. If the heat treatment time is too long, the phosphor particles will grow too much and the brightness of the phosphor will decrease, which is not preferable. In the former case, 10 hours,
The latter is limited to about 7 hours. For this reason, the optimum heat treatment time may be set depending on the amount of cesium chloride added and the heat treatment temperature. For comparison, SnO2:Eu phosphors having the same composition as above were prepared by the oxalate coprecipitation method and the metastannate coprecipitation method, respectively.

In the oxalate coprecipitation method, the heat treatment temperature was 1350°C and the heat treatment time was 2 hours, and in the metastannate coprecipitation method, the heat treatment temperature was 1300°C and the heat treatment time was 2 hours. The typical brightness of the resulting phosphors was 30 foot lamberts for the former and 33 lambert feet for the latter. As is clear from comparing the soil surface results with these values, the method of the present invention yields a phosphor exhibiting very good properties. In the method of the present invention, the raw materials are not limited to oxides, and salts that become oxides through thermal decomposition, such as hydroxides, oxalates, carbonates, acetates, etc. can also be used. .

As explained above, according to the method of the present invention, by utilizing the fluxing agent effect, grain growth of SnO2 and diffusion of Eu into it can be promoted and facilitated during heat treatment, which was difficult in the past. Thus, a brightly emitting SnO2:Eu phosphor can be obtained.

Since this method mainly involves mechanical mixing of raw materials and heat treatment, it is much easier to implement than the coprecipitation method, and the brightness of the luminescence of the resulting phosphor is also the same as that of the coprecipitation method. The manufacturing cost is also ridiculous.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the electron beam excitation emission spectrum of SnO2:Eu phosphor, and Fig. 2 is a cross-sectional view of an apparatus for exciting the phosphor obtained by the method of the present invention with a low-speed electron beam to emit light. , FIG. 3 is a diagram showing the structure of the grid electrode of this device.

Claims (1)

[Claims] 1. A mixture of stannic oxide or a tin salt that becomes stannic oxide through thermal decomposition, and europium oxide or a europium salt that becomes europium oxide through thermal decomposition,
1. A method for producing a europium-activated stannic oxide phosphor, which comprises adding cesium chloride as a fluxing agent and performing heat treatment. 2. Cesium chloride (CsCl) is added at a rate of 0.5 to 7% by weight based on the total amount of the mixture when converted to oxide. A method for producing a europium-activated stannic oxide phosphor. 3. The method for producing a europium-activated stannic oxide phosphor according to claim 1, wherein the heat treatment temperature is 1100 to 1500°C.