Chemistry of inorganic compounds – Halogen or compound thereof – Plural diverse halogens containing
Reexamination Certificate
2002-02-11
2004-12-07
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Plural diverse halogens containing
C423S497000, C250S484400, C252S30140H
Reexamination Certificate
active
06827920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preparing barium fluorohalide-based crystal, and particularly to a method for preparing a barium fluorohalide-based crystal useful as a phosphor material.
2. Description of the Related Art
It is desired that a crystal for use in oscillation of a laser or the like should have lattice defects reduced as much as possible. However, there are cases in which it is important to positively introduce a lattice defect into a crystal or glass and also to control the defect for the purpose of expressing a new optical functionality. A phenomenon of stimulated emission which has been remarked on in recent years is exhibited, principally by a combination of a crystal and a glass each having a large number of defects. Conventionally, there has been known a crystal represented by BaFX:Eu
2+
(wherein X=Br or I) having a defect such as a color center which emits light (instantaneous emission of light) in ranges from a near-ultraviolet region to a blue beam region by excitation thereof with radiation such as an X-ray, electron beam or ultraviolet ray. The crystal is used as a phosphor for a radiosensitive screen employed in radiography or the like.
Further, it has recently been found that, when the phosphor is irradiated with radiation such as an X-ray, electron beam or ultraviolet ray, and thereafter excited with an electromagnetic wave (excitation light) in ranges from a visible region to an infrared region, the phosphor emits light (stimulated emission) in ranges from a near-ultraviolet region to a blue beam region (hereinafter referred to as “stimulable characteristics”). Thus, the above-described phosphor has been noted especially useful as a phosphor for radiation image conversion panels which are used by radiation image recording and reproducing methods.
The above-described radiation image recording and reproducing method is organized in such a manner that radiation energy transmitted through a subject or emitted from an object to be examined is absorbed into a stimulable phosphor of a radiation image conversion panel. Thereafter, the stimulable phosphor is excited by an electromagnetic wave in a time sequential manner to thereby allow the radiation energy accumulated in the stimulable phosphor to emit as fluorescence. An electric signal is obtained by photoelectrically reading the fluorescence, and thereafter, based on the obtained electric signal, a visual image is produced on a recording material such as a photosensitive film, or on a display device such as a CRT.
The above-described phosphor is generally prepared by the following method. First, a mixture of phosphor raw materials is prepared by homogeneously mixing the phosphor raw materials in a dried state (a dry process) or by homogeneously mixing the phosphor raw materials in a slurry state and then drying (a wet process). Subsequently, the mixture of the phosphor raw materials is calcined, ordinarily at a temperature near a melting point of a host crystal (Ba, FX or the like) in a reducing atmosphere or the like substantially close to atmospheric pressure for several hours. Due to the calcining, the host crystal of the phosphor grows and, at the same time, activator elements are diffused in the host crystal. As a result, a color center which serves as a central source of stimulable emission is also generated.
A method for preparing barium fluorohalide-based crystal (hereinafter referred to as “BaFX-based crystal”) which serves as the host crystal in a phosphor material is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 7-233369 and 10-195431. However, in these conventional preparing methods, the BaFX-based crystal is obtained based on the following reaction formula (1). In this case, excessive halide ions (principally bromide ions) remain as a residue. As a result, there is a problem that raw materials may be substantially consumed wastefully or liquid stability may deteriorate.
NH
4
X+BaX
2
+AF→BaFX+NH
4
+
+A
+
+2X (1)
(in the above reaction formula (1), X represents a halogen atom and A
+
represents a positive ion such as NH
4
+
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for preparing barium fluorohalide-based crystal under conditions in which various raw materials such as halide ions in a preparing process are efficiently used, a residual portion of the raw materials is suppressed, and there is little variation in the amount of halide ions existing in a reactant mother liquor during preparation.
The above-described object can be achieved by the method for preparing barium fluorohalide-based crystal according to the present invention, which is described below. That is, the first aspect of the present invention is a method for preparing barium fluorohalide-based crystal, the method comprising the steps of: preparing a halide aqueous solution (A); preparing a halide aqueous solution (B) which includes a halogen the same as a halogen included in the halide aqueous solution (A); preparing a fluoride aqueous solution; preparing a barium salt aqueous solution; and thereafter mixing the halide aqueous solution (B), the fluoride aqueous solution and the barium salt aqueous solution into the halide aqueous solution (A) for generating a precipitate of BaFX-based crystals, in which X represents any of Br, Cl and I.
In accordance with a second aspect of the present invention, there is provided a method for preparing barium fluorohalide-based crystal, the method comprising steps of: providing a halide aqueous solution (A); providing a halide aqueous solution (B) which includes a halogen the same as a halogen included in the halide aqueous solution (A); and substantially simultaneously mixing each of at least the halide aqueous solution (B), a fluoride aqueous solution and a barium salt aqueous solution into the halide aqueous solution (A).
In accordance with a third aspect of the present invention, there is provided a method for preparing barium fluorohalide-based crystal, the method comprising the steps of: providing a halide aqueous solution (A); preparing a mixed solution of a fluoride aqueous solution and a halide aqueous solution (B) which includes a halogen the same as a halogen included in the halide aqueous solution (A); and substantially simultaneously mixing each of the mixed solution and a barium salt aqueous solution into the halide aqueous solution (A).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A barium fluorohalide-based crystal obtained by a method for preparing a barium fluorohalide-based crystal according to the present invention can be used not only for a phosphor material, but also in any field in which barium fluorohalide-based crystals are employed.
The method for preparing barium fluorohalide-based crystal according to the present invention includes at least a precipitate generating process in which a halide aqueous solution (B), a fluoride aqueous solution and a barium salt aqueous solution are mixed with a halide aqueous solution (A). The halide aqueous solution (B) contains the same halogen as that contained in the halide aqueous solution (A). A precipitate of BaFX-based crystal (X represents any of Br, Cl and I) is generated in a reactant mother liquor.
Further, as a process subsequent to the precipitate generating process, preferably, at least a separating process for separating the precipitate from the reactant mother liquor is provided. Moreover, as a process subsequent to the separating process, preferably, at least a calcination process for calcining the separated precipitate is provided. These processes will be described hereinafter.
[Precipitate Generating Process]
The precipitate generating process is a process in which the fluoride aqueous solution, the halide aqueous solution (B) and the barium salt aqueous solution are mixed into the halide aqueous solution (A), and a precipitate of BaFX-based crystal is generated.
Examples of the halogen contained in th
Fuji Photo Film Co. , Ltd.
Nguyen Ngoc-Yen
Sughrue & Mion, PLLC
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