JP2002105450A - Electron beam-excitation display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam-excitation display which is capable of improving brightness and resolution. SOLUTION: The electron beam-excitation display has a fluorescent screen (2) which comprises a phosphor having a composition expressed by (Y1-aXa)2 SiO5: Ln (wherein, X is at least one kind selected from the group consisting of Gd, La and Lu, a is 0-0.5, and Ln is Tb or Ce) and having an average particle diameter of 4.0-5.5 μm and a ratio of a major axis to a minor axis of 1.0-1.2, and has the fluorescent screen (2) which has a coated phosphor weight of 2.4-3.0 mg/cm2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display, such as a cathode ray tube or a field emission display, in which a phosphor is excited by an electron beam to emit light, and is particularly suitably applied to a projection tube.

[0002]

2. Description of the Related Art Conventionally, as a large-screen television for general home use, a CRT type projection display which is superior in cost is widely used. Projection displays are
Red, green and blue monochrome CRT (projection tube) images
This is a display of a method of enlarging and projecting onto a screen via a lens system. The monochrome CRT used for this display is required to have high brightness, and the demand for high resolution is increasing in accordance with the recent demand for high-quality image display.

The following phosphors are typically used for the projection tube from the viewpoint of luminance and luminance saturation characteristics under high current density excitation. That is, europium-activated yttrium oxide (Y ₂ O ₃ : Eu) is used as the red phosphor, and terbium-activated yttrium silicate (Y) is used as the green phosphor.
₂ SiO ₅ : Tb) and silver activated zinc sulfide (ZnS: Ag) as the blue phosphor. The brightness of the projection tube is not determined solely by the type of phosphor, but is also affected by the configuration of the phosphor film forming the phosphor screen. From the viewpoint of luminance, the fluorescent film needs to have a certain thickness, and a film in which two to three layers of particles are stacked is considered to be preferable. In a cathode ray tube having a high accelerating voltage, such as a projection tube, it is preferable that the phosphor has a large particle size. On the other hand, in order to increase the resolution, it is preferable that the thickness of the fluorescent film is thin.

As described above, when trying to set the thickness of the fluorescent film of the projection tube, the requirement from the luminance and the requirement from the resolution are in opposite directions, and either one must be sacrificed, and the luminance must be sacrificed. There is a problem that it is difficult to achieve both resolution and resolution.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electron beam excited display capable of improving luminance and greatly improving resolution.

[0006]

The electron beam excitation display of the present invention has a phosphor film coated with a phosphor, and irradiates the phosphor film with an electron beam to excite the phosphor to emit light. In the excitation display, the phosphor constituting the phosphor film is (Y _1-a X _a ) ₂ SiO ₅ : Ln (where X
Has a composition represented by at least one selected from the group consisting of Gd, La and Lu, a is 0 to 0.5, and Ln is Tb or Ce), and has an average particle size of 4.0 to 4.0. 5.
5 μm, the ratio of the major axis to the minor axis is 1.0 to 1.2, and the phosphor coating amount of the phosphor film is 2.4 to 3.0 mg / cm ^2.
It is characterized by being.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The display according to the present invention is of a type in which a phosphor is excited by an electron beam to emit light, and includes a cathode ray tube (CRT), a field emission display, and the like. The present invention is particularly effective for a projection tube used for magnifying and projecting an image on a screen via a lens system, in which resolution tends to be a problem.

In the present invention, the phosphor constituting the phosphor film on the phosphor screen is represented by the following general formula (Y ₁ -aX _a ) ₂ SiO ₅ : Ln (where X is selected from the group consisting of Gd, La and Lu). At least one, a is 0 to 0.5, Ln is Tb
Or Ce). Ln is T
The terbium-activated yttrium silicate phosphor b emits green light. The cerium-activated yttrium silicate phosphor in which Ln is Ce emits blue light. In each phosphor, part of yttrium (Y) is converted to gadolinium (G).
d), at least one element X selected from the group consisting of lanthanum (La) and ruthenium (Lu), and the ratio of the element X to yttrium (Y) is in the range of 0 to 0.5. is there. Within this range, light emission of a desired color can be obtained.

The present inventors have proposed a phosphor film using the above-mentioned phosphor, making the particle shape spherical, controlling the average particle diameter in an optimum range, and controlling the coating amount of the phosphor in an optimum range. It has been found that the formation of (1) can provide an electron beam excitation display with improved luminance and resolution.

In order to obtain a spherical phosphor, Japanese Patent Application No. Hei 6-270
222 and Japanese Patent Application No. 9-213884,
A method of treating a normal non-spherical phosphor with high-temperature plasma (thermal plasma method) can be used.

In the present invention, a spherical phosphor is used to increase the packing density of the phosphor in the phosphor film. In the present invention, the ratio between the major axis and the minor axis of the phosphor is set to 1.0 to 1.
The reason why the ratio is limited to the range of 2 is that if the ratio is larger than 1.2, particles that can no longer be regarded as spherical are increased, and sufficient light emission characteristics cannot be obtained due to a decrease in the packing density of the fluorescent film. is there. The ratio between the major axis and the minor axis is determined by observing the phosphor particle image with a scanning electron microscope or the like, measuring the maximum diameter and the minimum diameter of each of a plurality of arbitrarily selected particles, and determining the ratio. The average of the ratios is used.

In the present invention, the range of the average particle size of the phosphor is set to 4.0 to 5.5 μm. As the average particle size, the particle size when the integrated distribution curve obtained from the particle size distribution takes a value of 50%, that is, the 50% size is adopted. Specifically, a 50% diameter measured by a particle size distribution analyzer (LA-910W type, manufactured by Horiba, Ltd.) by a laser diffraction method is used. If the average particle size of the phosphor is out of the above range, the effect of improving both luminance and resolution, particularly luminance, cannot be obtained.

In the present invention, the coating amount of the phosphor on the phosphor film is controlled to an optimum range of 2.4 to 3.0 mg / cm ² . As described above, in order to increase the resolution, it is preferable that the film thickness is thin, that is, the amount of the phosphor applied per unit area is small. When using an existing non-spherical phosphor or a phosphor outside the range specified above even if it is spherical, it is impossible to improve both the luminance and the resolution, and one or both of the resolution and the luminance are not possible. Cannot be improved. On the other hand, if the spherical phosphor defined above is used and a phosphor film whose phosphor coating amount is controlled in the above range is formed, both luminance and resolution can be improved.

[0014]

The present invention will be described below in detail based on examples and comparative examples. FIG. 1 is a front view showing a part of the projection tube cut away. In FIG. 1, a fluorescent film 2 and an aluminum film 3 serving as a reflection film are formed on the inner surface of a face plate 1. An electron gun 4 and an anode 5 are provided to irradiate the fluorescent film 2 with an electron beam.

Various projection tubes were manufactured as described in the following examples and comparative examples. These projection tubes were evaluated based on brightness and resolution as follows.

Using the manufactured projection tube, a voltage of 32 kV was applied, and an electron beam was raster-scanned with a beam current of 3.5 mA to measure the luminance. 1 based on the luminance of Comparative Example 1
As a value of 00, the luminance measured in the other Examples and Comparative Examples was expressed as relative luminance and evaluated. According to the evaluation guideline, when the luminance was improved by 5% or more with respect to Comparative Example 1 (when the relative luminance was 105 or more), it was determined that the luminance was clearly improved.

The brightness profile was measured by drawing a straight line with a beam current of 1 mA using the manufactured projection tube. Assuming that the luminance at the center of the straight line was 100%, the spread of the line up to the position where the luminance decreased to 5% was defined as the spot diameter. The smaller the spot diameter, the better the resolution. In Comparative Example 1, the spot diameter was 250 μm. Based on this spot diameter, it was evaluated whether or not the resolution of other examples and comparative examples was improved. The evaluation guideline was 15 points for a spot diameter of 250 μm (Comparative Example 1).
%, It was determined that the resolution was clearly improved when the value was smaller (212.5 μm or less).

Comparative Example 1 A commercially available Y ₂ SiO ₅ : Tb phosphor having a non-spherical particle shape and an average particle size of 8.7 μm was used, and 1 cm was obtained by a known sedimentation method using a barium salt aqueous solution and water glass. ^A phosphor film was formed with an application amount of 4.2 mg per ² (not calculated because non-spherical phosphors have various shapes and it is meaningless to determine the ratio of the major axis to the minor axis). An organic film was formed on the fluorescent film, and aluminum was further evaporated to form an aluminum film having a thickness of about 0.2 μm. Through a process of attaching an electron gun and the like, a projection tube having a diagonal of 7 inches was manufactured.

Comparative Example 2 A projection tube was manufactured in the same manner as in Comparative Example 1 except that the phosphor used in Comparative Example 1 was used and a fluorescent film was formed at a coating amount of 3.0 mg / cm ² . . In this projection tube, the relative luminance was 99, which was lower than that of Comparative Example 1, and the spot diameter was 242 μm, and only a slight improvement was observed.

(Comparative Example 3) Y produced by pulverizing a commercial product and having a non-spherical particle shape and an average particle size of 5.2 μm was manufactured.
Comparative Example 1 except that a phosphor film was formed using a ₂ SiO ₅ : Tb phosphor and an application amount per cm ² of 2.7 mg.
A projection tube was produced in the same manner as described above. With respect to this projection tube, the relative luminance was 103, which was slightly improved as compared with Comparative Example 1, but was within the range of the characteristic variation, and the spot diameter was 234 μm, but the improvement was recognized, but not sufficiently improved.

(Comparative Examples 4 to 10, Examples 1 to 5) Non-spherical Y ₂ S having various average particle diameters which are commercially available or experimentally produced
Using iO ₅ : Tb phosphor as a raw material,
According to the methods disclosed in Japanese Patent Application No. 0222 and Japanese Patent Application No. 9-213884, spheroidization using thermal plasma and subsequent heat treatment are performed to obtain Y ₂ SiO ₅ having various average particle sizes:
A Tb spherical phosphor was obtained. A secondary electron microscope image of each spherical phosphor sample was taken, the major axis and the minor axis were measured for arbitrarily selected 20 particles, the ratio was calculated, and the average value was obtained. The average value was defined as the ratio between the major axis and the minor axis of each spherical phosphor sample.

Using these phosphors, phosphor films were formed at various coating amounts, and a projection tube was produced in the same manner as in Comparative Example 1. The brightness and resolution of each of the manufactured projection tubes were evaluated. Comparative Examples 4 to 10 and Examples 1 to 5
Table 1 shows the average particle size of the phosphor, the ratio of the major axis to the minor axis, the coating amount of the phosphor, the relative luminance, and the spot diameter.

[0023]

[Table 1]

As is clear from Table 1, in Examples 1 to 5, the luminance was improved by 5% or more compared to Comparative Example 1, and the luminance was improved by 15%.
The above-described reduction in spot diameter, that is, improvement in resolution can be achieved. 5 caused by variations in the manufacturing conditions of the projection tube
It can be seen that both the luminance and the resolution are clearly improved in the projection tubes of Examples 1 to 5 as compared with those of Comparative Example 1 even when the characteristic fluctuation of about% is considered.

(Comparative Example 11) By reducing the power of thermal plasma during spheroidization using thermal plasma, Y ₂ having a ratio of major axis to minor axis of 1.35 and an average particle diameter of 5.0 μm was obtained.
An SiO ₅ : Tb phosphor was obtained. A projection tube was prepared in the same manner as in Comparative Example 1, except that the fluorescent film was formed at an application amount of 2.7 mg per 1 cm ² . About this projection tube,
Although the relative luminance was 109, which was an improvement over Comparative Example 1, the spot diameter was 216 μm, which is not sufficiently improved.

In the above description, the terbium-activated yttrium silicate phosphor emitting green light has been described. However, part of yttrium is replaced by gadolinium (Gd) and lanthanum (L
It is also possible to use a phosphor substituted by at least one selected from the group consisting of a) and ruthenium (Lu). Also, instead of terbium (Tb), cerium (C
A blue emitting cerium-activated yttrium silicate phosphor containing e) can also be used. Further, the present invention can be applied to not only a projection tube but also a display excited by an electron beam, such as a normal cathode ray tube (CRT) and a field emission display.

[0027]

As described above in detail, according to the present invention, it is possible to provide an electron beam excited display such as a projection tube which can improve luminance and greatly improve resolution.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view of a projection tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Face plate 2 ... Fluorescent film 3 ... Aluminum film 4 ... Electron gun 5 ... Anode

Continuing on the front page (72) Inventor Hironobu Hattori 1-9-2, Hara-cho, Fukaya-shi, Saitama Pref. Inside the Toshiba Fukaya Plant Co., Ltd. F-term (reference) in Shiba Research Consulting Co., Ltd. 4H001 CA02 CA04 CA06 XA08 XA14 XA57 XA64 XA71 YA58 YA65 5C036 EE01 EF01 EF06 EF07 EG36 EH12

Claims (1)

[Claims] 1. An electron beam excitation display having a phosphor film coated with a phosphor and irradiating the phosphor film with an electron beam to excite the phosphor to emit light, wherein the phosphor constituting the phosphor film is (Y _1-a X _a ) ₂ SiO ₅ : Ln (where X is at least one selected from the group consisting of Gd, La and Lu, a is 0 to 0.5, Ln is Tb
Or Ce), the average particle size is 4.0 to 5.5 μm, and the ratio of the major axis to the minor axis is 1.0 to 1.
2, and the phosphor coating amount of the phosphor film is 2.4 to 3.0.
mg / cm ² .