JPH0892553A - Fluorescent substance - Google Patents

Abstract

PURPOSE: To obtain a fluorescent substance having excellent luminescent characteristics such as luminescent spectrum and sight sensitivity, capable of forming a dense fluorescent face having high luminance in using the fluorescent substance for a cathode ray tube or a fluorescent lamp. CONSTITUTION: This fluorescent substance has 0.5-20μm average particle diameter and the ratio of the major axis to the minor axis of each particle of 1.0-1.5 and is represented by the composition formula MWO4 (Ma is at least one of Ca and Mg) or CaWO4 :Pb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphor having excellent light emitting properties and coating properties when used in a cathode ray tube or a fluorescent lamp.

[0002]

2. Description of the Related Art Phosphors used in cathode ray tubes and fluorescent lamps are required to have a particle size of several μm from the viewpoint of luminous efficiency when excited by electron beams or ultraviolet rays. In order to obtain crystal grains having such a grain size, the phosphor is usually synthesized by firing and washing. However, the phosphor synthesized in this manner has a large amount of aggregation and is not a perfect spherical shape, and has a shape close to a polyhedron reflecting the shape and crystal structure of the raw material, and therefore the fluidity of the particles is not good.

[0003] When such a phosphor is used to form a fluorescent screen of a cathode ray tube, for example, there is a drawback that the light emission generated by electron beam excitation is not always sufficiently utilized as the light output from the fluorescent screen. That is, if the shape of the phosphor particles is close to a polyhedron and the fluidity is poor, a dense phosphor film cannot be obtained and voids are formed, and the smoothness of the aluminum back as a light reflecting film is poor, resulting in unevenness. Therefore, diffuse reflection of the emitted light becomes large, which causes a loss of light. Further, if there is a large amount of aggregation, a so-called inhomogeneous fluorescent film containing a lot of foreign matter is formed, which causes image blurring. Further, in the case of a color cathode ray tube, usually, a suspension (slurry) consisting of a glass inner surface and a photosensitive resin is applied over the entire surface to form a fluorescent film, and after irradiating ultraviolet rays to polymerize only a desired region, Rinse away the fluorescent film in the areas not exposed to ultraviolet light. At this time, if the light scattering of the fluorescent film is large, ultraviolet rays do not penetrate into the inside of the fluorescent film, so that the inside is less likely to polymerize. Therefore, it is difficult to form a sufficiently thick film that maximizes the brightness of the fluorescent film. further,
If the light scattering is large, a region other than the desired region is exposed to light and polymerized, so that it becomes difficult to obtain a fluorescent film pattern as designed. Similarly, when the above fluorescent material is used in a fluorescent lamp, a dense fluorescent film cannot be obtained, so that the light emission due to the ultraviolet excitation is not effectively utilized sufficiently.

Here, MWO ₄ (where M is at least one of Ca and Mg) or CaWO ₄ : Pb
Any of the above phosphors has an emission spectrum having a peak wavelength in the range of 400 to 500 nm and emits light of a short wavelength, which is disadvantageous in terms of visibility. In addition, for example, CaWO ₄ : P
The peak of the excitation spectrum such as b is shifted to the longer wavelength side than 254 nm, and there is a problem that the excitation efficiency is lowered when excited by ultraviolet rays of 254 nm.

[0005]

DISCLOSURE OF THE INVENTION The present invention is capable of forming a phosphor screen which is excellent in light emission characteristics such as light emission spectrum and luminosity and which is dense and uniform and has high brightness when used in a cathode ray tube or a fluorescent lamp. It is intended to provide a phosphor.

[0006]

The phosphor of the present invention has an average particle size of 0.5 to 20 μm, and the ratio of the major axis to the minor axis of each particle is in the range of 1.0 to 1.5. , Particle size 0.2 μm
The composition formula MWO ₄ (provided that M is 0.001 to 5% by weight, preferably 0.01 to 1% by weight) contains the following ultrafine particles.
Is at least one of Ca and Mg) or CaW
It is characterized by being represented by O ₄ : Pb.

The present invention will be described in more detail below. In the present invention, the average particle diameter of the phosphor particles is 0.5 to 20 μm.
The reason why m is defined is that it is empirically known that the optimum particle size for use in a cathode ray tube or a fluorescent lamp is in this range. That is, the average particle size is 0.
When it is smaller than 5 μm or larger than 20 μm, the brightness of the phosphor screen becomes low.

In the phosphor of the present invention, the ratio of the major axis to the minor axis of each phosphor particle, that is, the ratio (aspect ratio) of the maximum diameter portion and the minimum diameter portion of each phosphor particle is 1.0.
It is in the range of ~ 15 and has a shape very close to a perfect sphere. The phosphor particles of the present invention contain 0.001 to 5% by weight, preferably 0.01% by weight of ultrafine particles having a particle size of 0.2 μm or less.
~ 1% by weight. If the ultrafine particles are contained in an amount of more than 5% by weight, light scattering increases, so that the light transmittance of the fluorescent film produced from this fluorescent material decreases, and the practicality becomes poor.
On the other hand, the inclusion of ultrafine particles within the above range improves the fluidity and dispersibility of the phosphor. For this reason, when the fluorescent film is formed by the sedimentation of the fluorescent material in the liquid or the application of the fluorescent material slurry, the fluorescent film becomes close to the closest packing. Therefore, diffused reflection in the fluorescent film is reduced, the transmittance of the film is improved, the ratio of light emission used as light output from the fluorescent screen is increased, and the brightness of the fluorescent screen is improved. On the other hand, during heat treatment of a color cathode ray tube or the like, the ultrafine particles act as a binder between spherical particles, and the adhesive force of the fluorescent film is strengthened.

Regarding the emission characteristics of the phosphor of the present invention, since the emission spectrum is shifted to the long wavelength side, the luminous efficiency becomes bright. On the other hand, the excitation spectrum is 254 nm
Since the deviation from is small, when excited by ultraviolet rays of 254 nm, the excitation light efficiency is improved and the brightness of the fluorescent film is improved.

The phosphor of the present invention can be produced by melting phosphor powder particles as a raw material in high frequency thermal plasma and then rapidly cooling it. The phosphor powder as a raw material is usually produced by preparing a precipitate by a wet method, followed by baking and washing, and it is preferable that the primary particle size is about 2 μm or more. This is because when the primary particle size is small and is, for example, 1 μm or less, the entire particles are melted and evaporated, and the particles obtained by quenching are often 0.2 μm or less. Further, even when the particle size is 2 μm or more, a part thereof is evaporated, so that ultrafine particles of 0.2 μm or less adhere to the surface of the obtained particles. The particle size of the obtained phosphor is substantially the same as the particle size of the raw phosphor when the dispersibility of the phosphor used as the raw material is good. Therefore, the particle size of the obtained phosphor can be controlled by the particle size of the phosphor as a raw material and the degree of aggregation.

In order to obtain a phosphor having a shape close to a perfect sphere, which is the object of the present invention, it is necessary that the raw material particles are not entirely evaporated and the surface of the particles is completely melted. However, this can be achieved by adjusting the power of the high frequency thermal plasma and the supply amount of the raw material phosphor into the plasma. A spherical fluorescent substance having a ratio of major axis to minor axis in the range of 1.0 to 1.5 by melting the particle surface under these conditions and rapidly solidifying while maintaining the spherical shape by the surface tension. Can be obtained. When this phosphor contains a large amount of ultrafine particles of 0.2 μm or less,
By ultrasonic cleaning and discarding the supernatant,
A phosphor of the present invention containing 0.001 to 5% by weight, preferably 0.01 to 1% by weight, of ultrafine particles of 0.2 μm or less is obtained.

[0012]

Embodiments of the present invention will be described below. (Comparative Example 1) CaWO ₄ was prepared by an ordinary wet precipitation / calcination method.
A phosphor (Comparative Example 1) was prepared. The average particle size of this phosphor measured by the Blaine method was 4.3 μm. When excited by ultraviolet rays or electron beams, the peak wavelength of the emission spectrum of this phosphor was 411 nm. The chromaticity value is x =
It was 0.165 and y = 0.120.

Example 1 Using the CaWO ₄ phosphor of Comparative Example 1 as a raw material, a mixed gas of argon and oxygen was supplied as a carrier gas into a high frequency thermal plasma, and the phosphor was melted and rapidly cooled (Example 1). ) Got. The average particle size of the obtained phosphor was measured by the Blaine method to be 3.9 μm.
It was m. An electron micrograph of the obtained phosphor is shown in FIG. The ratio of the major axis to the minor axis of each phosphor particle obtained from this electron micrograph was in the range of 1.00 to 1.08. The same phosphor of 0.2 μm or less generated by partial evaporation of the raw material particles adheres to the particle surface of the obtained phosphor, but after the ultrasonic cleaning, the supernatant liquid is discarded to 0.1% by weight of ultrafine particles of 2 μm or less
The contained phosphor was obtained. It was also confirmed that the X-ray diffraction pattern of this phosphor was that of CaWO ₄ .

When the emission spectrum of this phosphor was measured by ultraviolet or electron beam excitation, the peak wavelength was 433 nm, which was 20 nm or more longer than the spectrum of the phosphor of Comparative Example 1 on the long wavelength side. Therefore, the chromaticity values were x = 0.173 and y = 1.44. When this phosphor was excited by ultraviolet rays of 254 nm and the powder brightness was measured, it was 78% with respect to the phosphor of Comparative Example 1. Moreover, when the powder luminance was measured by exciting this phosphor with an electron beam having an accelerating voltage of 10 kV and a current density of 0.5 μA / cm ² , it was about 102% with respect to the phosphor of Comparative Example 1.

Next, a precipitation method is carried out using this phosphor.
When a fluorescent film having a coating amount of 10 mg / cm ² was formed and the transmittance was measured, a light transmittance 1.7 times that of the fluorescent film formed using the phosphor of Comparative Example 1 was obtained.

A phosphor screen having a coating amount of 6 mg / cm ² was formed by a sedimentation method using the obtained phosphor, and after applying an aluminum back, an electron gun was attached, exhausted and sealed, and a 7-inch cathode wire was attached. A tube was made. About this cathode ray tube, acceleration voltage 3
When the brightness was measured under the conditions of 0 kV and a beam current of 500 μA, it was 118% with respect to the cathode ray tube similarly manufactured using the phosphor of Comparative Example 1.

(Comparative Example 2) A CaWO ₄ : Pb phosphor (Comparative Example 2) was produced by a conventional wet precipitation / calcination method.
The average particle size of this phosphor measured by the Blaine method is 3.
It was 6 μm. The peak wavelength of the emission spectrum of this phosphor excited by ultraviolet rays or electrons was 435 nm. The chromaticity values were x = 0.172 and y = 1.169. The peak wavelength of the excitation spectrum was located at 270 nm.

Example 2 CaWO ₄ : Pb of Comparative Example 2
A phosphor (Example 2) was obtained by using a phosphor as a raw material, supplying a mixed gas of argon and oxygen as a carrier gas into high-frequency thermal plasma, and melting and quenching. When the average particle size of the obtained phosphor was measured by the Blaine method,
It was 3.1 μm. The ratio of the major axis to the minor axis of each phosphor particle obtained from the electron micrograph is 1.00 to 1.
It was in the range of 11. The obtained phosphor was ultrasonically washed and the supernatant was discarded to obtain a phosphor containing 0.05% by weight of ultrafine particles of 0.2 μm or less. Moreover, it was confirmed that the X-ray diffraction pattern of this phosphor was that of CaWO ₄ : Pb.

When the emission spectrum of this phosphor was measured by ultraviolet or electron beam excitation, the peak wavelength was 458 nm, and the chromaticity values were x = 0.180 and y =.
It was 0.186. The excitation spectrum is 259n
m, and the deviation from 254 nm was slight. When this phosphor was excited by ultraviolet rays of 254 nm and the powder brightness was measured, it was 105% with respect to the phosphor of Comparative Example 2. Further, when this phosphor was excited with an electron beam having an accelerating voltage of 10 kV and a current density of 0.5 μA / cm ² , the powder brightness was measured and found to be about 103% of that of the phosphor of Comparative Example 2.

Next, by using this phosphor by a sedimentation method,
When a fluorescent film having a coating amount of 9 mg / cm ² was formed and the transmittance was measured, a light transmittance 1.8 times that of the fluorescent film formed using the phosphor of Comparative Example 2 was obtained.

A phosphor screen having a coating amount of 6 mg / cm ² was formed by a precipitation method using the obtained phosphor, and after applying an aluminum back, an electron gun was attached, exhausted and sealed, and a 7-inch cathode ray was attached. A tube was made. About this cathode ray tube, acceleration voltage 3
When the luminance was measured under the conditions of 0 kV and a beam current of 500 μA, it was 121% with respect to the cathode ray tube similarly produced using the phosphor of Comparative Example 2.

(Comparative Example 3) A MgWO ₄ phosphor (Comparative Example 3) was manufactured by a conventional wet precipitation / calcination method. The average particle size of this phosphor measured by the Blaine method was 4.2 μm. The peak wavelength of the emission spectrum of this phosphor excited by ultraviolet rays or electron beams was 498 nm. The chromaticity values were x = 0.225 and y = 0.418.

Example 3 Using the MgWO ₄ phosphor of Comparative Example 3 as a raw material, a mixed gas of argon and oxygen was supplied as a carrier gas into high frequency thermal plasma, and the phosphor was melted and rapidly cooled (Example 3). ) Got. When the average particle size of the obtained phosphor was measured by the Blaine method, it was 4.0.
was μm. The ratio of the major axis to the minor axis of each phosphor particle obtained from the electron micrograph was in the range of 1.00 to 1.07. The obtained phosphor was ultrasonically washed and the supernatant was discarded to obtain a phosphor containing 0.2% by weight of ultrafine particles of 0.2 μm or less. It was also confirmed that the X-ray diffraction pattern of this phosphor was that of MgWO ₄ .

When the emission spectrum of this phosphor by ultraviolet or electron beam excitation was measured, the peak wavelength was 512 nm, and the chromaticity value was x = 0.233, y =
It was 0.441. The excitation spectrum is 254n
It was deviated to the shorter wavelength side than m. 254n this phosphor
When the powder brightness was measured by exciting with ultraviolet light of m, it was 114% with respect to the phosphor of Comparative Example 3. In addition, this phosphor was used with an acceleration voltage of 10 kV and a current density of 0.5 μA / cm ^2.
When the powder luminance was measured by exciting with the electron beam of No. 3, it was about 109% with respect to the phosphor of Comparative Example 3. in this way,
Compared with the phosphor of Comparative Example 3, the phosphor of Example 3 has a larger excitation spectrum when it is excited by ultraviolet light and has a higher emission efficiency than the phosphor of Comparative Example 3.

Next, by using this phosphor, a sedimentation method is carried out.
When a fluorescent film having a coating amount of 12 mg / cm ² was formed and the transmittance was measured, a light transmittance 1.5 times that of the fluorescent film formed using the phosphor of Comparative Example 3 was obtained.

A phosphor screen having a coating amount of 6 mg / cm ² was formed by using the obtained phosphor by a precipitation method, and after applying an aluminum back, an electron gun was attached, exhausted and sealed, and a 7-inch cathode wire was attached. A tube was made. About this cathode ray tube, acceleration voltage 3
When the luminance was measured under the conditions of 0 kV and a beam current of 500 μA, it was 115% with respect to the cathode ray tube similarly produced using the phosphor of Comparative Example 3.

[0027]

As described above in detail, according to the present invention, it is possible to provide a fluorescent substance which is bright in terms of visual sensitivity and has high emission luminance upon excitation by ultraviolet rays of 254 nm. Further, when used in a cathode ray tube or a fluorescent lamp, a fluorescent screen having a high transmittance and excellent in compactness and homogeneity can be formed, so that a cathode ray tube or a fluorescent lamp having high brightness can be obtained. Even when this phosphor is used in a circular or compact type fluorescent lamp, a large improvement in brightness can be achieved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a particle structure of a phosphor of Example 1 of the present invention.

Front page continuation (72) Inventor Miwa Okumura 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (2)

[Claims] 1. Ultrafine particles having an average particle size of 0.5 to 20 μm, a ratio of major axis to minor axis of individual particles in the range of 1.0 to 1.5, and having a particle size of 0.2 μm or less. Compositional formula MWO ₄ containing 0.001 to 5% by weight (where M is Ca and M
and at least one of g) or CaWO ₄ : Pb. 2. An ultrafine particle having a particle diameter of 0.2 μm or less is 0.0
The phosphor according to claim 1, comprising 1 to 1% by weight.