JPS6119688A - Blue-emitting phosphor and blue-emitting cathode ray tube containing the same for use in color projection type picture tube - Google Patents

Abstract

PURPOSE:To provide the titled phosphor which has excellent chemical stability and high blue light-emitting efficiency during the irradiation of electron beam and X-rays, consisting of a specified Ce-activated lanthanum gadolinium oxybromide. CONSTITUTION:An oxygen source and La source such as La2O3 or La2(CO3)3, an oxygen source and Gd source such as Gd2O3 or Gd2(CO3)3, a Br source, and an oxygen source and Ce source such as CeO2 or Ce2(CO3)3.8H2O are blended in such a proportion as to give a molar ratio of La to Ce of 0.3-25, and they are thoroughly mixed in a ball mill. The mixture is fired in the presence of carbon or in a reducing atmosphere at 800-1,500 deg.C for 0.5-5hr, washed with water and dried at 80-130 deg.C to obtain a blue-emitting phosphor composed of a Ce- activated lanthanum gadolinium oxybromide contg. La and Gd in a molar ratio of 0.3-25. The phosphor is suspended in water contg. waterglass and Ba(NO3)2, the suspension is applied to the inner surface of a cathode ray tube and left to stand to form a phosphor screen on a face plate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a blue-emitting phosphor and a blue-emitting cathode ray tube for a color projection type video device using the same in a phosphor screen, and more particularly, to By using a chemically stable phosphor with high blue luminous efficiency when irradiated with radiation, the luminous efficiency does not decrease even when the temperature of the phosphor screen increases, and color reproducibility is excellent. The present invention relates to a blue-emitting cathode ray tube for color projection video devices.

[Technical background of the invention and its problems]

A color system that combines independent high-brightness color cathode ray tubes that emit light in the three primary colors of blue, green, and red, and then magnifies the images on each of these cathode ray tubes using optical lenses and projects them onto a large projection screen to reproduce a color image. Projection type video devices are currently commercially available. Conventionally, this video device reproduces television images and is often used for educational and entertainment purposes, but in the future, as the screens of television broadcasting and video systems become more precise (higher density scanning), It is expected that its range of applications will further expand.

Each of the cathode ray tubes constituting this device is equipped with a phosphor screen on the inner surface of its face, which is a luminescent screen made of a film of each phosphor that emits light in each primary color.

In this device, in order to make the brightness of the projected image on the large projection screen as high as possible, the phosphor screen of each of the above-mentioned cathode ray tubes is 1.
It is necessary to irradiate the electron beam with 0 times or more energy.

Therefore, in this device, the temperature of the phosphor screen rises to over 60° C. under normal operating conditions. This is an inconvenient situation because generally speaking, as the temperature of the phosphor screen increases, the brightness of the phosphor screen decreases accordingly.

In order to deal with this situation, it is possible to form a phosphor screen using a phosphor that allows the phosphor screen to emit light at the highest possible brightness and its luminous efficiency will not decrease even if the temperature of the phosphor screen rises. requested.

Each color-emitting cathode ray tube has a red fluorescent screen.

Various phosphors that emit light in green and blue colors are used, but among these, silver-activated sulfide M (ZnS :Ag) is used.

By the way, what is required in this device is that when a white image is reproduced from each cathode ray tube onto a large projection screen, the initial white image does not change over a long period of time.

To achieve this, the red color that makes up the fluorescent screen of each cathode ray tube,
It is necessary that the luminescent colors of the blue and green phosphors do not change even when the temperature rises, and that the current-luminance saturation characteristics (gamma characteristics) are the same. 7 From this point of view, when considering the relationship between the above-mentioned blue-emitting phosphors and Japanese roof tiles, the following facts become clear. First, both the red light-emitting phosphor and the green light-emitting phosphor show little change in emission color even when the temperature rises, and furthermore, their gamma characteristics are almost the same.

However, blue-emitting phosphor (ZnS:Ag)
The color of the emitted light varies between the initial room temperature (25°C) and the normal operating temperature (8°C).
(0°C), the situation is quite different.

For example, when the projection tube is operated at 28 kV and 200 μA, the chromaticity value is 25°C (x = 0.147, y =
o, o 74), 80°C (x=0.147, y=o
, o 82), and the color of the emitted light differs between the initial stage and during normal operation as the temperature rises. This is because as the temperature of the phosphor rises, the emission in the long wavelength region becomes stronger.Also, the gamma characteristics of this ZnS:Ag are considerably worse than those of the red-emitting phosphor and the green-emitting phosphor. For example, when the projection tube is operated at 28 kV and 200 .mu.A and the brightness factor per current is 100, the value at a current of 1200 .mu.A is as low as 46.

For this reason, in conventional color projection video devices, when a white image is reproduced on a large projection screen using Zns:Ag as a blue-emitting phosphor, Zns
S: As the temperature of Ag rises, a difference occurs in the emitted light color, and the white image becomes distorted due to the initial change over time about 10 minutes after the start of image projection. Furthermore, even when in operation,
Due to the poor gamma characteristics of ZnS:Ag, the white images will be different in the case of low electron beam energy injection and in the case of high electron beam energy injection, and in order to readjust it, complex electric This creates an inconvenient problem in that a correction is required.

In addition to the above-mentioned problems, blue-emitting cathode ray tubes equipped with a phosphor screen made of ZnS:Ag also have the following problems from the perspective of color image reproduction, just like direct-view color cathode ray tubes. There is.

That is, normally, in order to widen the color reproduction range of an image on the CIE chromaticity diagram, the emitted color of a blue-emitting phosphor is set at a coordinate point whose chromaticity point is as close as possible to the edge of the chromaticity diagram. However, the emission color of ZnS:Ag in the operating state is x=0.147,
The problem is that the purity of the blue color is low at a distance from the edge of the chromaticity diagram (y=Q, Q82).

In addition to the above-mentioned ZnS:Ag, cerium-activated rare earth oxyhalide-based phosphors are known as blue-emitting phosphors that exhibit high luminous efficiency when excited by electron beams.

For example, in the Journal of Chemical Physics, Vol. 47 (1967), G. Brussel et al. described YOCI:Ce as a phosphor for flying spot scanners.
, La0C1:Ce, and La0Br:Ce. Further, Japanese Patent Publication No. 54-38996 discloses T, aOBr:Ce as a phosphor for an X-ray screen. However, although these SE1 and RAM-activated rare earth oxybromides have the advantage of high luminous efficiency during X-ray excitation, they have the disadvantage that they easily adsorb moisture in the air, reducing the initial luminous efficiency. Furthermore, when a fluorescent film is formed using these phosphors on the inner surface of the face of a cathode ray tube, the fluorescent film tends to peel off from the inner face of the face, making it impractical. Therefore, in order to prevent the above-mentioned adsorption of moisture in the air, JP-A-53-131987 discloses LnOX:Ce (where Ln is Y) as a cerium-activated rare earth oxybromide.

At least one selected from La and Gd; X is C1
At least one type of ゜Br) is disclosed and this LnOX:
It has been proposed to coat Ce particles with rare earth oxychloride to prevent the above adsorption and maintain the initial luminous efficiency. However, this method has the problem of complicating the manufacturing process of the phosphor and reducing productivity. Furthermore, the phosphor screen of the blue-emitting cathode ray tube of a color projection image device is subject to the following harsh conditions. Since it is necessary to fully satisfy the following conditions, the phosphor itself is also required to satisfy the following conditions. In other words,■
Good color reproducibility of the Cassie display; ■No reduction in luminous efficiency at high temperatures (above 60°C); ■High luminance characteristics; ■Little change over time; ■Excellent chemical stability. , ■ Excellent afterglow properties, etc.

[Purpose of the invention]

Among the blue-emitting phosphors mentioned above, a cerium-activated lanthanum gadolinium oxybromide phosphor, which has higher luminance and chemical stability than the cerium-activated rare earth oxybromide that has been proposed so far, and its phosphor are used. An object of the present invention is to provide a blue light beam tube for a color projection type image device, which has excellent color reproducibility and high luminous efficiency at high temperatures.

[Summary of the Invention] As a result of extensive research into a cerium-activated rare earth oxybromide phosphor that does not have the above drawbacks and has high brightness, the inventors have discovered that lanthanum and gadolinium exist as rare earths in a mixed crystal form. , and the molar composition ratio of lanthanum and gadolinium is within the range described below. Cerium-activated lanthanum gadolinium oxybromide phosphors are cerium-activated lanthanum oxybromide phosphors and cerium-activated lanthanum oxybromide phosphors in which lanthanum and gadolinium each exist alone as rare earth elements. Having discovered the fact that it has superior brightness and chemical stability compared to gadolinium oxybromide phosphors, we have completed the phosphor of the present invention and a blue-emitting cathode ray tube for color projection video devices using this phosphor. It has arrived.

That is, the blue-emitting phosphor of the present invention is characterized by being composed of cerium-activated syntungadolinium oxybromide in which the molar composition ratio of lanthanum and gadolinium is 0.3 to 25. The blue-emitting cathode ray tube for use in the present invention is characterized in that the phosphor screen is made of the above-mentioned phosphor.

The phosphor of the present invention is a mixed crystal type cerium-activated lanthanum gadolinium oxybromide in which the molar composition ratio of lanthanum and gadolinium is 0.3 to 25. In the phosphor of the present invention, when the molar composition ratio (La/Gd-) is less than 0.3, the brightness is lower than that of cerium-activated lanthanum oxybromide or cerium-activated gadolinium oxybromide containing lanthanum or gadolinium alone. However, when La/Gd exceeds 25, not only does the brightness not become particularly high compared to cerium-activated lanthanum oxybromide or cerium-activated gadolinium oxybromide, but it also becomes chemically stable. In the present invention, the activation amount of cerium is preferably in the range of 0.1 to 3% by weight. If the activation amount of cerium deviates from this range, the luminance of the phosphor will decrease, and therefore the luminance of blue-emitting cathode ray tubes using this phosphor will also decrease, so it is recommended not to combine it with red- and green-emitting cathode ray tubes. When,
This causes a decrease in the brightness of white images.

The phosphor of the present invention is prepared as follows.

That is, first of all, lantaf oxide (L!L203), L
az(CO3)a.

Lanthanum and oxygen sources such as La2(C204)3.9H20; Gadolinium oxide (Gd20a), G
d2(COa)a.

Gadolinium and oxygen sources such as Qd2 (C204)3.9H20; ammonyl bromide A (NE (4Br)
, HBr, CzHsBr; cerium oxide (CeOz).

Cez (CO3)3-8H20, CeC1a・7Hz
After weighing a predetermined amount of a cerium source and an oxygen source, they are thoroughly mixed using, for example, a ball mill. The resulting mixture was placed in a quartz crucible, and an appropriate amount of carbon, such as activated carbon, was placed on top of the mixture, and then heated at 800 to 1500°C.
The mixture is baked at a temperature of 0.5 to 5 hours. In addition, when carbon is not placed on the mixture, the crucible is placed in a reducing atmosphere, for example, nitrogen gas containing 2 to 5% hydrogen, and the mixture is fired in this reducing atmosphere. After the obtained fired product is cooled, it is placed in a nylon mesh and sieved with water, and then thoroughly washed with water, for example, after replacing the water with ethanol, it is filtered, and dried at a temperature of 80 to 130°C. A phosphor of the invention is obtained.

In manufacturing the blue-emitting cathode ray tube for a color projection type imaging device of the present invention, a sedimentation method and a slurry method are used.

Manufacturing methods such as printing methods are applicable, and sedimentation methods are particularly preferred. When the sedimentation method is applied, a phosphor film of the above-mentioned phosphor is formed on the inner surface of the face of a cathode ray tube using a sedimentation liquid of water glass and barium nitrate in an appropriate ratio.

[Embodiments of the invention]

Examples 1 to 6 (1) Preparation of phosphors and measurement of solubility As raw materials for phosphors, lanthanum oxide Q, a20a), gadolinium oxide (Gd20a), ammonium bromide (N
H+Br) 50 f, cerium oxide Ce0z) o
, 1st were prepared, La2O3 and Qd203 were weighed in the proportions shown in the table, and these were thoroughly mixed in a ball mill. In the table, the composition ratio of lanthanum and gadolinium is indicated by the weight ratio A/B.The obtained mixed powder was placed in a quartz crucible, an appropriate amount of activated carbon was placed on top of it, and the lid was closed. It was baked at 1300°C for 2 hours. The obtained baked powder was placed in a 7-unit nylon bag, sieved with water, thoroughly washed with pure water, replaced with ethanol, filtered, and dried at about 120°C to obtain the indicated blending ratio. Six different types of cerium-activated lanthanum gadolinium oxybromide were obtained. For comparison, a comparative example was prepared in which the composition ratio of lanthanum and gadolinium was outside the range of the present invention.

The chemical stability of each phosphor was investigated by measuring the solubility of each phosphor according to the following specifications.

Solubility of phosphor: weight of phosphor after firing (Wl),
The weight (Wo)Wl-'VJv of the phosphor after washing for 3 hours with pure water at a temperature of 20[deg.] C. was measured, and the solubility of the phosphor was calculated using the following formula -Ken-x1 (%).

The above results are summarized in the table.

As a result, as is clear from the table, the phosphors of Examples have low solubility and are chemically stable, whereas the phosphors of Comparative Examples have high solubility and are unstable, and in some cases enter a colloid state, which is difficult to prepare. It turned out to be undesirable.

(2) Measurement of powder brightness increase rate The powder brightness increase rate of each phosphor with various changes in La/Gd was measured under the following specifications, and the results are shown in FIG.

This rate of increase is a numerical representation of how much the luminance of the phosphor of the present invention improves over the luminance of the conventional cerium-activated lanthanum oxybromide phosphor.

Powder brightness increase rate: A cerium-activated lanthanum gadolinium bromide phosphor was packed in a sample dish, irradiated with an electron beam at an accelerating voltage of 10 kV and a current density of 1 μA/J, and the brightness (Ll) at that time was measured. ,cerium.

Activated lanthanum oxybromide firefly The luminous body also shines in the same way. Measure the degree (LO) and use the following formula Calculated by 1111 part = x 100 (a).

As shown in FIG. 1 (the horizontal axis in the figure is a logarithmic scale), the phosphor of the present invention has a maximum luminance of 120 cm higher than that of the cerium-activated lanthanum oxybromide phosphor, and the molar composition ratio is 0. It was found that the brightness increased by 60% or more in the range of .3 to 25. Note that similar results were obtained for cerium-activated gadolinium oxybromide.

(3) Effect of cerium activation amount on brightness Next, the relationship between the activation amount of cerium and the brightness of the phosphor is shown in FIG. 2 (the horizontal axis in the figure is on a logarithmic scale). In this case, the substances other than cerium and their blending amounts are the same as in Example 4. Curve 1 in FIG. 2 is the activation amount vs. brightness curve when the firing temperature is 1100°C, and curve 2 is the It is an activation amount-luminance curve when the temperature is 1300°C. The same electron beam used in the calculation of the powder brightness increase rate was used for the brightness measurement. No.
As is clear from Figure 22, it was found that the brightness was high when the activation amount of cerium was in the range of 0.1 to 3% by weight of the entire phosphor, and that when it was out of this range, the brightness decreased.

(Xun) For the production of blue-emitting cathode ray tubes and their characteristics,
Blue-emitting cathode ray tubes for color projection video devices were manufactured using phosphors with different La/Gd ratios. That is, a phosphor suspension was prepared by suspending 0.8 f of the above phosphor powder in an aqueous solution containing pure water and water glass (K2O.3SiO2) with a concentration of 25. A 2% concentration barium nitrate solution and pure water were added to a Finch cathode ray tube so that the total amount was 4001 nl, and the mixture was left standing.The above-mentioned phosphor suspension was then poured into the tube, and the mixture was left undisturbed for 30 minutes. It was quiet. The phosphor precipitated and a fluorescent film was formed. Thereafter, the supernatant liquid was poured off. A fluorescent screen was formed on the inner face of the cathode ray tube. In each sedimentation solution, the amount of water glass with a concentration of 25 μm was used in an amount of 30 m, and the amount of barium nitrate with a concentration of 2% was used in a amount of 15 μm.

A lacquer film was applied to the obtained phosphor screen to form an organic film, and an aluminum film was further deposited on this film. After painting, an electron gun was attached to complete the cathode ray tube of the present invention.

The degree to which the brightness of the cathode ray tube obtained in this way is improved compared to the brightness of a cathode ray tube using cerium-activated rank oxybromide phosphor is expressed by the brightness improvement rate of the following specifications, and the brightness improvement rate and molar Composition ratio IJ/
The relationship with Gd is shown in Figure 3 (the horizontal axis in the figure is on a logarithmic scale).

Brightness improvement rate: The cathode ray tube of the present invention was used at an accelerating voltage of 28 kV.
, electron beam current 1200μA.

After stabilizing with a raster size of 130 x 100- for 3 hours in steady operation, the brightness (L2) of this cathode ray tube was measured, and a Bralan tube using cerium-activated lanthanum oxybromide phosphor was tested with the same specifications as above. After manufacturing and stabilizing in the same manner, the luminance (L6) L2=Lo' was measured and calculated using the following formula -r, X100 (a).

As shown in Figure 3, the brightness of the cathode ray tube of the present invention is improved by up to 150% compared to a cathode ray tube using cerium-activated lanthanum oxybromide phosphor, and the molar composition ratio is in the range of 0.3 to 25. It was found that the brightness was improved by more than 6 degrees.

Next, a blue-emitting cathode ray tube using the phosphor of Example 4,
A red-emitting cathode ray tube with Y2O3: Eu as the phosphor screen and a green-emitting cathode ray tube with La0C1: Tb as the phosphor screen were each operated under an accelerating voltage of 28 Kv (80 Kv).
The gamma characteristics were measured by emitting light at 10°C.

The results are shown in FIG. 4. In FIG. 4, the relative brightness is shown with the brightness when irradiated with an electron beam of 200 μA as 100. In the figure, curve a is that of Example 4, and curve b is La0
C1 is that of Tb, C is that of Y2O3:Eu, and d is that of ZnS:Ag shown for comparison.

As is clear from FIG. 4, the blue-emitting cathode ray tube of the present invention has significantly better gamma characteristics than the conventional one (ZnS:Ag), which is 1.8 to 1.9 times better at 1200 μA. In addition, blue, red, and green cathode ray tubes are
Their gamma characteristics center around blue, and this means that when these three cathode ray tubes are combined into a color projection device, extremely stable white images can be reproduced under operating conditions (80 degrees Celsius). This suggests that it can be obtained.

Note that since the gamma characteristics of each of the above-mentioned phosphors are relatively uniform, even if the acceleration voltage of each is reduced to some extent, there is almost no change in the emission color and only a slight decrease in brightness occurs. This means that by lowering the accelerating voltage, stability can be improved and the speed at which the electron beam impinges on the phosphor screen can be reduced, making it possible to extend its life by that amount.

Next, the operating conditions of the blue-emitting cathode ray tube of the present invention (80°C
), and the results are shown as curve A in FIG. 5. The end of the curve is the emission spectrum for zns:Ag shown for comparison. In the figure, the luminescence energy on the vertical axis is normalized with the peak of luminescence energy as 100.

As is clear from FIG. 5, in the case of ZnS:Ag, since the position of the emission spectrum is on the long wavelength side, there is a possibility that the color reproduction range will be narrowed when combined with red and green emitting cathode ray tubes. On the other hand, in a cathode ray tube using the phosphor according to the present invention, the position of the emission spectrum is shifted toward the short wavelength side, so that the color reproduction range is widened.

In order to confirm this, the color of the emitted light when the blue-emitting cathode ray tube using the phosphor of Example 4 was operated at 28 kV and 1200 μA was measured, and its chromaticity point is shown as B1 in FIG.

B2 is the chromaticity point of a conventional cathode ray tube whose fluorescent screen is ZnS:Ag. Bl (x=0.154, y
=0.062), B2 (X=0.147, y=0
．． As is clear from the 7° diagram, R and G in the figure represent the chromaticity points of the emitted light of the red and green luminescent plows/tubes using Y2O3:Eu and La0C1:Tb, respectively. In addition, since B1 is located closer to the edge of the CIE chromaticity diagram than B2, it can be seen that the purity of blue light emission is good and the color reproduction range is wide.

When the blue-emitting cathode ray tube of the present invention was installed in a projection type imaging device and the visibility was evaluated, the focus on the projection screen was good and the projected color image was bright even in the high electron beam current region. Furthermore, since there was little decrease in luminous efficiency due to the rise in temperature of the cathode ray tube, color images did not change over time.

〔Effect of the invention〕

As is clear from the above, the blue-emitting phosphor of the present invention is
Compared to conventional cerium-activated rare earth oxyfluoride phosphors that only contain either Shinken or Gadolinium, the brightness is significantly higher9, and the phosphor has low solubility and is chemically stable. Improves sex.

Furthermore, when the w-color emitting cathode ray tube of the present invention using the blue-emitting phosphor of the present invention is installed in a color projection video device, the temperature of the phosphor screen rises to the operating temperature (80°C). Also, the gamma characteristics are similar to those of red-emitting cathode ray tubes, green-emitting cathode ray tubes, etc., and there is no change over time, so the color reproducibility is excellent.
Furthermore, as is clear from the chromaticity diagram, the purity of the blue color is excellent and the color reproduction range is widened, which is of great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the composition ratio of lanthanum and gadolinium and the powder brightness increase rate of the phosphor of the present invention, FIG. 2 is a characteristic diagram showing the relationship between the activation amount of cerium and the brightness, and FIG. Fig. 3 is a characteristic diagram showing the relationship between the composition ratio of lanthanum and gadolinium and the brightness improvement rate of the cathode ray tube of the present invention, Fig. 4 is a characteristic diagram showing the gamma characteristics of the cathode ray tube, Fig. 5 is a diagram of the emission spectrum, and Fig. The figure is a CIK chromaticity characteristic diagram showing the emission chromaticity region of the emission color. Figure 4 Electron a t, r txsd, A) Figure 5 Slope t (nm)

Claims (1)

[Claims] 1. The molar composition ratio of lanthanum and gadolinium is 0.3 to 2.
5, a blue-emitting phosphor comprising cerium-activated lanthanum gadolinium oxybromide. 2. The blue-emitting phosphor according to claim 1, wherein the activation amount of cerium is 0.1 to 3% by weight. 3. A blue color projection type image device, characterized in that the phosphor screen is composed of a blue-emitting phosphor made of cerium-activated lanthanum-gadolinium oxybromide, with a molar composition ratio of lanthanum and gadolinium of 0.3 to 25. Luminescent cathode ray tube.