Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
2000-12-11
2003-03-11
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
Reexamination Certificate
active
06531073
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rare earth activated alkaline earth metal fluorohalide stimulable phosphor, a method for preparing the stimulable phosphor and a radiation image conversion panel by the use of the stimulable phosphor.
BACKGROUND OF THE INVENTION
As an effective means for replacing conventional radiography is known a recording and reproducing method of radiation images using stimulable phosphors described in JP-A No. 55-12148 (hereinafter, the term, JP-A refers to an unexamined and published Japanese Patent Application).
In the method, a radiation image conversion panel (hereinafter, also simply denoted as panel) comprising a stimulable phosphor is employed, and the method comprises the steps of causing the stimulable phosphor of the panel to absorb radiation having passed through an object or having radiated from an object, sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as “stimulating rays”) to release the radiation energy stored in the phosphor as light emission (stimulated emission), photoelectrically detecting the emitted light to obtain electrical signals, and reproducing the radiation image of the object as a visible image from the electrical signals. The panel having been read out is subjected to image-erasing and prepared for the next photographing cycle. Thus, the radiation image conversion panel can be used repeatedly.
In the radiation image recording and reproducing methods described above, a radiation image is advantageously obtained with a sufficient amount of information by applying radiation to an object at a considerably smaller dose, as compared to conventional radiography employing a combination of a radiographic film and a radiographic intensifying screen. Further, in the conventional radiography, the radiographic film is consumed for every photographing; on the other hand, in this radiation image converting method, in which the radiation image conversion panel is employed repeatedly, is also advantageous in terms of conservation of resources and economic efficiency.
The radiation image conversion panel employed in the radiation image recording and reproducing method basically comprises a support and provided thereon a phosphor layer (stimulable phosphor layer), provided that, in cases where the phosphor layer is self-supporting, the support is not necessarily required. The stimulable phosphor layer comprises a stimulable phosphor dispersed in a binder. There is also known a stimulable phosphor layer, which is formed by vacuum evaporation or a sintering process, free from a binder, and which comprises an aggregated stimulable phosphor. There is further known a radiation image conversion panel in which a polymeric material is contained in the openings among the aggregated stimulable phosphor. On the surface of the stimulable phosphor layer (i.e., the surface which is not in contact with the support) is conventionally provided a protective layer comprising a polymeric film or an evaporated inorganic membrane to protect the phosphor layer from chemical deterioration and physical shock.
The stimulable phosphor, after being exposed to radiation, produces stimulated emission upon exposure to the stimulating ray. In practical use, phosphors are employed, which exhibit an emission within a wavelength region of 300 to 500 nm stimulated by stimulating light of wavelengths of 400 to 900 nm. Examples of such stimulable phosphors include rare earth activated alkaline earth metal fluorohalide phosphors described in JP-A Nos. 55-12145, 55-160078, 56-74175, 56-116777, 57-23673, 57-23675, 58-206678, 59-27289, 59-27980, 59-56479 and 59-56480; bivalent europium activated alkaline earth metal fluorohalide phosphors described in JP-A Nos. 59-75200, 6-84381, 60-106752, 60-166379, 60-221483, 60-228592, 60-228593, 61-23679, 61-120882, 61-120883, 61-120885, 61-235486 and 61-235487; rare earth element activated oxyhalide phosphors described in JP-A 59-12144; cerium activated trivalent metal oxyhalide phosphors described in JP-A No. 55-69281; bismuth activated alkaline metal halide phosphors described in JP-A No. 60-70484; bivalent europium activated alkaline earth metal halophosphate phosphors described in JP-A Nos. 60-141783 and 60-157100; bivalent europium activated alkaline earth metal haloborate phosphors described in JP-A No. 60-157099; bivalent europium activated alkaline earth metal hydrogenated halide phosphors described in JP-A 60-217354; cerium activated rare earth complex halide phosphors described in JP-A Nos. 61-21173 and 61-21182; cerium activated rare earth halophosphate phosphors described in JP-A No. 61-40390; bivalent europium activated cesium rubidium halide phosphors described in JP-A No. 60-78151; bivalent europium activated cerium halide rubidium phosphors described in JP-A No. 60-78151; bivalent europium activated composite halide phosphors described in JP-A No. 60-78153. Specifically, iodide-containing bivalent europium activated alkaline earth metal fluorohalide phosphors, iodide containing rare earth metal activated oxyhalide phosphors and iodide containing bismuth activated alkaline earth metal halide phosphors exhibited stimulated emission of high luminance.
Along with the spread of radiation image conversion panels employing stimulable phosphors is further desired an enhancement of radiation image quality, such as enhancements of sharpness and graininess.
The foregoing preparation methods of stimulable phosphors are called a solid phase process or calcination method, in which pulverization after calcination is indispensable and there were problems such that it was difficult to control the particle form affecting sensitivity and image performance.
Of means for enhancing image quality of radiation images are valid preparation of fine particles of a stimulable phosphor and enhancing particle size uniformity of the fine stimulable phosphor particles, i.e., narrowing the particle size distribution.
Preparation of stimulable phosphors in the liquid phase described in JP-A 9-291278 and 7-233369 is a method of obtaining a stimulable phosphor precursor in the form of fine particles by adjusting the concentration of a phosphor raw material solution, which is valid as a method of preparing stimulable phosphor powder having narrow particle size distribution. From the thus obtained phosphor precursor, a stimulable phosphor was obtained by subjecting the precursor to calcination at high temperature to provide stimulated light-emissive ability but its stimulated emission intensity was not sufficient. The radiation image conversion plate employing such a stimulable phosphor exhibiting a relatively low stimulated emission intensity leads to one having a low sensitivity, so that more dose is required to obtain radiation images having image quality of the same level.
SUMMARY OF THE INVENTION
An object of the present invention is to obtain a rare earth activated alkaline earth metal fluorohalide stimulable phosphor exhibiting high luminance, to obtain enhanced stimulated emission intensity in a rare earth activated alkaline earth metal fluorohalide stimulable phosphor comprised of fine particles with high homogeneity of the particle size distribution, and to provide a radiation image conversion panel employing the rare earth activated alkaline earth metal fluorohalide stimulable phosphor and exhibiting high sensitivity and high image quality.
An object of the present invention is to enhance the stimulated light emission intensity, i.e., sensitivity of a stimulable phosphor and to provide a rare earth activated alkaline earth metal fluoroiodide stimulable phosphor exhibiting superior sharpness and graininess, a preparation method thereof and a radiation image conversion panel by the use thereof.
An object of the present invention is to provide a method for preparing a impurity-free stimulable phosphor, in which the preparation process is shortened.
The above object of the invention can be accomplished by the following embodiments:
1. A method f
Itoh Hiroto
Kobayashi Isao
Maezawa Akihiro
Masutomi Haruhiko
Nakano Yasushi
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
Koslow C. Melissa
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