JPH10251635A - Production of fluorescent substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a spherical particulate BaFX-base fluorescent substance having high luminous efficiency and good dispersibility by treating a specified fluorescent substance powder in a nonoxidizing high-temperature gas stream. SOLUTION: A raw material phosphor powder having a constitution of the formula BaFX:R (wherein X is at least one halogen element selected from F, Cl, Br and I; and R is at least one element selected from lanthanide group elements) is fed into a high-frequency hot-plasma treatment device, where it is subjected to heat treatment in a nonoxidizing high-temperature gas stream under conditions under which at least 5% of the fluorescent substance powder serving as war material is vaporized. Fluorescent substance particles melted in the high-temperature gas stream and solidified, with particle diameters close to those of raw material particles are collected by a cyclone, while the particulate phosphor vaporized from raw material particles in the high-temperature gas stream and solidified is collected by a filter. The fine particles collected by a filter are recovered to give spherical fine phosphor particles having a mean diameter of 0.05-1μm, preferably 0.1-0.2μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a BaFX-based fine particle phosphor.

[0002]

[Prior art]

BaFX: R (X is at least one halogen element selected from the group consisting of F, Cl, Br and I, and R is at least one element selected from the group consisting of lanthanide groups). Phosphors are known to be useful as X-ray intensifying screens, X-ray imaging plates or hole burning recording materials.

For example, US Pat. No. 4,080,306 discloses that
The phosphor obtained by substituting a small amount of divalent europium for barium of BaFX shows efficient light emission in the ultraviolet to blue region by X-ray irradiation. When the phosphor screen coated with this phosphor is combined with a regular type photographic film, X It describes that a line image can be suitably sensitized and recorded. Japanese Patent Application Laid-Open No. 6-9956 discloses that when the halogen element of a BaFX-based phosphor is made smaller than the stoichiometric composition, a color center is formed by X-ray irradiation, and when this is irradiated with red light, blue light emission (so-called bright light) is obtained. (Emitted light emission) occurs efficiently. Therefore, an X-ray image is recorded as a latent image using the phosphor screen formed by applying the phosphor, and a blue light emission image can be reproduced by irradiating the latent image with a red laser beam.

Further, in Solid State Communication Magazine Vol. 99, No. 10, pp. 759-762, a phosphor in which barium of BaFX is replaced by a small amount of divalent samarium, and holes are formed in an absorption spectrum band by laser light irradiation. It is shown that the memory can be reproduced by optically storing the data and observing a change in the fluorescence intensity caused by the optical storage. Further, the BaFX-based phosphor has high luminous efficiency by electron beam irradiation, and can be applied to a light emitting device using an electron beam.

In any of the above-mentioned applications, a BaFX-based phosphor powder is applied to a substrate to form a phosphor screen, and the phosphor used at this time has a particle size of several μm or more. This means that in general industrial applications, the particle size is 2 to 10
This corresponds to the use of a μm inorganic phosphor. The reason why the particle size of the phosphor is set in the above range for general industrial use is as follows. That is, when the phosphor is manufactured by the flux method, the luminous efficiency can be optimized when the particle diameter is in the above range. On the other hand, if the particle size is smaller than the above range,
It is said that luminous efficiency decreases. It is considered that this is because when the particle diameter decreases, the surface of each particle is covered with the non-light-emitting layer, and the proportion of the non-light-emitting layer increases. For example, the technical report of the Institute of Television Engineers of Japan ED-754, 2
One page, FIG. 6, shows that the ZnS phosphor produced by the flux method has a particle diameter of 1 μm compared to a particle having a particle diameter of 7 μm.
It is shown that luminous efficiency is reduced to about 10 to 50% in the case of about. By extrapolating this, light emission is at a level that cannot be expected with a particle diameter of 100 nm or less.

However, when a BaFX-based phosphor is used for, for example, an X-ray intensifying screen, it is necessary to reduce the particle size of the phosphor to obtain higher resolution. In addition, two layers, a phosphor screen containing a phosphor having a small particle diameter and a phosphor screen containing a phosphor having a large particle diameter, are sequentially formed on the substrate, and light emitted from the large particles is reflected by the small particles so that the direction opposite to the substrate is reflected. It is effective to improve the luminous efficiency of the phosphor screen by increasing the amount of light traveling to the fluorescent screen. Further, a BaFX-based phosphor having a small particle diameter may be mixed with another X-ray phosphor such as CaWO ₄ for use. For these purposes, it is desirable to use a BaFX-based phosphor which has a high luminous efficiency despite having a particle diameter of less than 1 μm, has good dispersibility, and has excellent granularity.

Usually, a BaFX phosphor is prepared by mixing a base material (barium halide) and an activator source (eg, europium halide) with a flux (eg, an alkali halide) in an inert atmosphere at 600 to 800 ° C. It is manufactured by a method of firing and solid-phase reaction. However, according to this method, agglomeration due to adhesion of particles is large, and dispersibility deteriorates. Further, BaFX has a crystal structure belonging to the PbFX type, so that the particle shape tends to be flat. The light emission from the phosphor having such a flat particle shape is not isotropic, and the light emission from the phosphor screen emits more components in the horizontal direction than in the vertical direction. For this reason, when photographing light from the phosphor screen, background noise is large, that is, graininess is deteriorated.

Various methods can be considered for producing the BaFX-based phosphor in the form of fine particles, but a suitable method is not known. For example, when fine particles are formed by a mechanical method such as ball milling, the luminous efficiency is reduced. The above-mentioned US Pat. No. 4,080,306 describes a method in which BaF ₂ and BaX ₂ are stirred and reacted in water, and then the aggregated particles are fired together with a flux.
The following particles have not been obtained. JP-A-6-99 mentioned above
No. 56 proposes a method in which BaFX flat primary particles are granulated by a spray-drying method, and the granulated particles are fired to be spherical. However, the phosphor obtained by this method is not perfectly spherical because the shape of flat primary particles remains, and the phosphor is not perfectly spherical.
No fine particles of μm or less were obtained.

On the other hand, the present inventors have proposed a method of cooling an oxide-based or sulfide-based phosphor by melting it in thermal plasma (Japanese Patent Application No. 5-227008). However, it has been found that the luminous efficiency of a phosphor having a particle diameter of about 0.1 μm obtained by this method is 50% or less as compared with a phosphor having a particle diameter of several μm. This can be explained by the reason that as the particle diameter decreases, the ratio of the non-light emitting layer on the particle surface increases, and the luminous efficiency decreases. From these results, it was expected that the luminous efficiency would be reduced when the BaFX-based phosphor was also made into fine particles.

[0010]

An object of the present invention is to provide a method for producing a spherical BaFX-based fine particle phosphor having high luminous efficiency and good dispersibility.

[0011]

According to the present invention, there is provided a method for producing a phosphor, comprising the following general formula: BaFX: R (X is at least one halogen element selected from the group consisting of F, Cl, Br and I; Is at least one element selected from the group consisting of lanthanides.) A phosphor powder having a composition represented by the following formula:
Treated in a non-oxidizing high-temperature air stream, average particle size 0.05 to
It is characterized in that fine particles of 1 μm are obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS To manufacture the phosphor of the present invention,
General formula BaFX: R (X is at least one halogen element selected from the group consisting of F, Cl, Br and I,
R is at least one element selected from the group consisting of lanthanides. The phosphor powder having the composition represented by the formula (1) is used as a raw material and is treated in a non-oxidizing high-temperature gas stream.

In the method of the present invention, a phosphor powder having a particle diameter of several μm produced by a usual flux method is used as a raw material. As a processing apparatus, for example, Japanese Patent Application Laid-Open No. 8-109
375 can be used. In the present invention, the phosphor powder as a raw material is made to have a non-oxidizing atmosphere because europium or samarium, which is an activator that partially replaces barium when the phosphor is oxidized, changes from divalent to trivalent. This is because the emission color changes significantly.

In the method of the present invention, by adjusting the power of the high-frequency thermal plasma and the supply amount of the raw material phosphor into the plasma, the treatment is performed under the condition that the raw material phosphor is not only melted but also evaporated. In general, the evaporation rate can be increased as the power of the plasma is stronger and the supply amount of the raw material phosphor is smaller. Then, a cyclone and a filter are further provided downstream of the reaction vessel, and the fluorescent particles having a particle diameter close to the raw material particles that have been melted and solidified in the high-temperature airflow are collected by the cyclone. The fine particle phosphor evaporated and solidified is collected by a filter. Thus, the fine particles collected by the filter are collected.

In the present invention, it is preferable to set a condition under which at least 5% or more of the phosphor powder as a raw material evaporates. This is because when the evaporation rate of the raw material phosphor is less than 5%, changes in the lattice constant and emission spectrum between the particles collected by the cyclone and the particles collected by the filter are recognized. This suggests that the phosphor composition changes somewhat.

In the case where the phosphor fine particles recovered from the filter contain phosphor particles having a particle diameter exceeding 1 μm close to the raw phosphor, the particles are irradiated with ultrasonic waves in a liquid. The phosphor particles having a large particle diameter may be settled and removed.

The BaFX-based phosphor fine particles recovered by the filter according to the method of the present invention can have a particle size of 0.05 to 1 μm by adjusting the conditions of the thermal plasma treatment, and can be used even if the particle size is small. Regardless, the luminous efficiency is high, and the sphere can be formed into a spherical shape with good dispersibility. Previous studies by the present inventors have shown that oxides or oxysulfides have a particle size of 10 to 10 when vaporized and solidified in a thermal plasma.
It is known that fine particles of about 0 nm can be obtained,
As described above, such a fine particle phosphor has poor luminous efficiency. On the other hand, it is known that when zinc oxide or zinc sulfide is vaporized and solidified in thermal plasma, needle-like or flat fine particles are obtained. On the other hand, BaFX
In the case of a system phosphor, the luminous efficiency of fine particles having a particle diameter of 0.05 to 1 μm obtained by evaporating and quenching in thermal plasma is 80% or more of the luminous efficiency of the raw phosphor, and in some cases, higher than that of the raw phosphor. The luminous efficiency also increases. BaFX like this
In the case of the system phosphor, unexpected results exceeding the range inferred from other phosphors can be obtained. However, the reasons for these results are unclear at present. According to the results of X-ray diffraction, it was confirmed that the crystal structure of the raw material phosphor and the fine particle phosphor solidified by evaporation did not change, and that the lattice constant did not change under the above-described plasma conditions. Was done.

The BaFX-based fine particle phosphor obtained by the method of the present invention can be suitably used for, for example, an X-ray intensifying screen. For example, in an X-ray intensifying screen having a structure in which a phosphor screen containing a phosphor having a small particle diameter and a phosphor screen containing a phosphor having a large particle diameter are sequentially formed on a substrate, BaFX is used as a phosphor having a small particle diameter. Based fine particle phosphor can be used. Also, another X-ray phosphor such as CaWO ₄ and a BaFX-based fine particle phosphor can be mixed and used.

The phosphor of the present invention has an average particle diameter of 0.05 to
The reason why the thickness is set to 1 μm is as follows. That is, if the thickness is less than 0.05 μm, the luminous efficiency is reduced, and
When used as a phosphor screen (reflection layer) or a phosphor mixture containing a phosphor having a small particle size in the use of an X-ray intensifying screen, the light scattering is too small to be suitable. If the particle diameter is too small, it becomes difficult to handle the powder. On the other hand, if it exceeds 1 μm, high resolution cannot be obtained. Also, X
The particle size is too large to be used for the reflective layer in line intensifying screen applications, and uniform mixing becomes difficult when used as a mixed phosphor. For these purposes, it is more preferable to make the particle diameter smaller than 0.5 μm.

The phosphor of the present invention emits light efficiently even by electron beam irradiation. This can be used to label biological reactions such as antigen-antibody reactions. That is, the fluorescent substance of the present invention is attached to a living tissue or an antigen or an antibody, and the position of the living tissue or the antigen or the antibody can be known by observing a cathodoluminescence image. In this case, it is preferable that the particle diameter of the phosphor does not exceed 0.1 μm. Conversely, when a fluorescent material is used as a label by attaching a living tissue or an antigen or an antibody around the fluorescent material particles, the particle size is desirably 0.1 to 1 μm.

The phosphor of the present invention can be applied to a fluorescent ink. That is, since the particle diameter is small and the dispersibility is excellent, the rate of settling in the liquid is small. Therefore,
Clogging does not easily occur during printing, and a printed matter with high luminous efficiency can be produced by electron beam or X-ray irradiation. For example, the present invention can be applied to a fluorescent ink or the like for authenticating securities. In this case, the average particle size is 0.1 to 0.2 μ
m is more desirable.

[0022]

Embodiments of the present invention will be described below. Example 1 In this example, BaFCl: Eu phosphor fine particles were manufactured. First, was suspended BaF ₂ particles in an excess of BaCl ₂ aqueous solution than the stoichiometric composition of BaFCl, BaF ₂ is Ba
Stir well until FCl. Then, to remove BaCl ₂ of water and excess filtering the suspension. The obtained BaFCl is suspended again in water, and an appropriate amount of EuF is added thereto.
₂ and EuCl ₃ were added and mixed well. This suspension was filtered again, and the obtained powder was dried. This powder was fired at 700 ° C. in a nitrogen atmosphere. After cooling, the powder was washed with water to obtain a BaFCl: Eu phosphor. The average particle diameter of the phosphor determined by the Blaine method was 4 μm.

The phosphor was supplied into a high-frequency thermal plasma having a frequency of 4 MHz and an output of 10 kW using argon gas as a carrier. A part of the phosphor was melted, escaped from the thermal plasma, rapidly cooled, and collected by a cyclone provided downstream of the thermal plasma device. Part of the phosphor was evaporated and quenched into fine particles, which were collected by a filter provided further downstream of the cyclone.

The ratio of the fine particles recovered by the filter was 15% by weight as compared with the raw material phosphor charged into the apparatus. The particle size of the fine particles was measured by transmission electron microscopy. As a result, the average particle diameter was 0.2 μm, and the proportion of particles having a particle diameter of 1 μm or more was 1% or less. Particles having a particle diameter of 0.05 μm or less included those having a non-spherical particle shape, but those having a particle diameter of 0.1 μm or more were almost spherical.

FIG. 1 shows an X-ray diffraction diagram of the fine particles. From the width and position of the diffraction line, it can be seen that the obtained fine particles are BaFCl having good crystallinity. FIG. 2 shows an emission spectrum when the obtained phosphor is excited by an electron beam of 10 kV and 0.5 μA / cm ² . The emission peak position was at 380 to 385 nm, which is the same as that of the phosphor before the thermal plasma treatment. The half width of the emission band was slightly reduced. The height of the emission peak was 17% higher than that of the phosphor before the thermal plasma treatment.

For comparison, the phosphor before thermal plasma treatment was pulverized with a ball mill to obtain a powder having an average particle diameter of 0.5 μm (Comparative Example 1). Using the phosphors of Example 1 and Comparative Example 1, a phosphor film having a thickness of 5 mm was formed, and a X-ray of 80 kV was formed.
Irradiates X-rays from the X-ray tube and changes the emission output to KL made by Toshiba Glass
Measured through a 39 interference filter. As a result, in Example 1, a light emission output five times that of Comparative Example 1 was obtained.

Example 2 A BaFBr: Eu phosphor was prepared in the same manner as in Example 1. The average particle size of the phosphor obtained by the Blaine method is 4.7.
μm. Next, this phosphor was subjected to thermal plasma treatment under the same conditions as in Example 1, and fine particles were collected with a filter.
The recovery rate of the fine particles was 20%. X-ray diffraction showed that the obtained fine particles were BaFBr having good crystallinity.

FIG. 3 shows an emission spectrum when the obtained phosphor is excited by an electron beam under the same conditions as in Example 1. The emission peak position was at 385 to 390 nm similarly to the phosphor before the thermal plasma treatment, and the shape of the spectral band was almost the same. The emission peak height was 16% higher than that of the phosphor before the thermal plasma treatment.

On the other hand, the phosphor before the thermal plasma treatment was pulverized to obtain a powder having an average particle diameter of 0.4 μm (Comparative Example 2). A phosphor film having a thickness of 5 mm was formed using the phosphors of Example 2 and Comparative Example 2, and the luminescence output was measured by X-ray excitation under the same conditions as described above. As a result, in Example 2, a light emission output six times or more that of Comparative Example 2 was obtained.

[0030]

As described in detail above, according to the present invention, a spherical BaFX-based fine particle phosphor having high luminous efficiency and good dispersibility can be manufactured.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a phosphor of Example 1.

FIG. 2 is an emission spectrum diagram of the phosphor of Example 1.

FIG. 3 is an emission spectrum diagram of the phosphor of Example 2.

Continuing from the front page (72) Naoto Matsuda, Inventor 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Miwa Okumura 1 Kosuka-Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Inside the Toshiba R & D Center (72) Inventor Yoshiaki Inoue 5983 Tamura, Hikarizuka-shi, Kanagawa Prefecture High-frequency refining stock company (72) Inventor Seiji Yokota 5983, Tamura, Hiratsuka-shi, Kanagawa Prefecture High-frequency heat refining stock company (72) Inventor Kazuhiro Kawasaki 5893 Tamura, Hiratsuka-shi, Kanagawa Pref. Inside the company (72) Inventor Akira Terashima 5983 Tamura, Hiratsuka-shi, Kanagawa Pref. Heat-melting stock company

Claims (2)

[Claims] 1. The following general formula: BaFX: R (X is at least one halogen element selected from the group consisting of F, Cl, Br and I, and R is at least one halogen element selected from the group consisting of lanthanide group) A phosphor powder having a composition represented by the following formula:
Treated in a non-oxidizing high-temperature air stream, average particle size 0.05 to
A method for producing a phosphor, wherein fine particles of 1 μm are obtained. 2. The method for producing a phosphor according to claim 1, wherein fine particles having an average particle diameter of 0.05 to 1 μm which have been evaporated and solidified from the phosphor powder as a raw material are recovered.