Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Utility Patent
1999-04-14
2001-01-02
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C252S30140R
Utility Patent
active
06168730
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a stimulable phosphor, a method for preparing the stimulable phosphor and a radiation image conversion panel comprising the stimulable phosphor.
BACKGROUND OF THE INVENTION
As a method replacing a conventional radiography, there is known a radiation image recording and reproducing method utilizing stimulable phosphor, as described in JP-A No. 55-12145 (herein, the term “JP-A” means an unexamined and published Japanese Patent Application). In the method, a radiation image converting panel (in other words, an image storage phosphor sheet) 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 electric signals, and reproducing the radiation image of the object as a visible image from the electric signals. The panel having been read out is subjected to image-erasing and prepared for the next photographing cycle. Thus, the radiation image converting panel can be used repeatedly.
In the radiation image recording and reproducing methods described above, 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 converting panel is employed repeatedly, is also advantageous in terms of conservation of resources and economic efficiency.
The radiation image converting 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 comprises an aggregated stimulable phosphor. There is further known a radiation image converting 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, exhibits 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 with wavelengths of 400 to 900 nm. Examples of the 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 55-12144; 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; and bivalent europium activated complex halide phosphors described in JP-A No. 60-78151. Of these stimulable phosphors described above, iodide containing europium activated alkaline earth metal fluorohalide phosphors, iodide containing rare earth element activated oxyhalide phosphors and iodide containing bismuth activated alkaline metal halide phosphors exhibit stimulated emission with high luminance.
Along with advancement of utilization of the radiation image conversion method employing a stimulable phosphor, there have been desired further enhancements of radiation image quality such as enhanced sharpness and enhanced graininess. Effective as means for enhancing radiation image quality are making the stimulable phosphor grains finer and further homogenizing the grain size of the fine-grained phosphor, i.e., enhancing homogeneity of the grain size distribution of the fine-grained phosphor.
JP-A Nos. 9-291278 and 7-233369 disclose a method for preparing a stimulable phosphor in a liquid phase, in which a fine-grained stimulable phosphor precursor is obtained by adjusting the concentration of a phosphor raw material solution, providing an effective technique of preparing a homogeneous fine-grained phosphor powder. A stimulable phosphor can be prepared by further subjecting the thus prepared phosphor precursor to calcination at high temperature to obtain stimulated emission capability. However, it has been proved that the stimulated emission intensity achieved by conventionally known calcining methods was insufficient. The use of a stimulable phosphor with low emission intensity to prepare a radiation image conversion plate leads to reduced sensitivity of the radiation image conversion plate, producing a disadvantage such as increasing the dose necessary to obtain a radiation image having the same image quality.
Conventional Calcining Method of Precursor
A rare earth activated alkaline earth metal fluorohalide stimulable phosphor precursor, which has conventionally been prepared by the known liquid phase method, is subjected to calcination according to the following procedure. As is disclosed in JP-A 9-291278, dried precursor crystals are weighed and thereto is added fine-grained oxide powder as an anti-sintering agent, such super-fine alumina powder or super-fine silica powder. Subsequently, the resulting mixture is introduced into a refractory vessel such as a silica boat, an alumina crucible or a silica crucible and subjected to calcining in the core portion of an electric furnace, wherein the calcining temperature is optimally within the range of 400 to 1300° C. and the calcining time is 0.5 to 12 hrs. Calcining is conducted in a neutral atmosphere such as a nitrogen gas or argon gas atmosphere, or in a weakly reductive atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas, or further in an atmosphere containing a small amount of oxygen.
The calcining method described above (so-called liquid phase process) is substantially the same as the method, in which a precursor comprised of raw material powder is directly subjected to calcining to obtain a stimulable phosphor, being so-called solid phase process. Preparation of the stimulable phosphor by the solid phase method is detailed in JP-B Nos. 1-26640, 63-55555 and 63-28955. The solid phase process is different from the method
Kawabata Kanae
Masutomi Haruhiko
Nabeta Hiroyuki
Wakamatsu Hideaki
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
Koslow C. Melissa
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