Fluorescent substance, method for production thereof, radiation detector using the fluorescent substance, and X-ray CT apparatus using the radiation detector

Claim 1

A fluorescent substance comprising a rare earth oxysulfide represented by the chemical formula R 2 (1-x) Pr 2x O 2 S, wherein R stands for at least one member selected from the group consisting of Y, Gd, La, and Lu and x for a numerical value satisfying the expression, 5×10 -5 ≦x≦1×10 -2 , and containing a measurable amount of PO 4 not exceeding 15 ppm.

Claim 7

A method for the production of a fluorescent substance characterized by the steps of: mixing a powder of a rare earth oxide represented by the chemical formula, R 2 O 3 , and containing Pr in an amount in the range of from 5×10 -5 to 1×10 -2 mol with sulfur (S), a phosphate represented by the chemical formula, A 3 PO 4 , and a carbonate represented by the formula, A 2 CO 3 , so as to form a mixture containing a rare earth oxysulfide composition represented by the chemical formula, R 2 (1-x) Pr 2x O 2 S, firing said mixture at a temperature in the range of from 1100° C. to 1300° C. thereby mainly forming a fired substance of a rare earth oxysulfide represented by the chemical formula, R 2 (1-x) Pr 2x O 2 S, washing said fired substance with an acid and water, and subjecting said washed material to hot isostatic pressing at a temperature of not less than 1400° C. under a pressure of not less than 100 MPa thereby forming a rare earth oxysulfide ceramic containing PO 4 in an amount not more than 15 ppm, wherein R stands for at least one member selected from the group consisting of Y, Gd, La and Lu and A for at least one member selected from the group consisting of Li, Na, K, Rb, and Cs, and x satisfies the expression, 1×10 -5 ≦x≦5×10 -2 .

Claim 8

A method for the production of a fluorescent substance characterized by the steps of: mixing a powder of a rare earth oxide represented by the chemical formula, R 2 O 3 , and containing Pr in an amount in the range of from 5×10 -5 to 1×10 -2 mol with sulfur (S), a phosphate represented by the chemical formula, A 3 PO 4 , and a carbonate represented by the formula, A 2 CO 3 , so as to form a mixture containing a rare earth oxysulfide composition represented by the chemical formula, R 2 (1-x) Pr 2x O 2 S, firing said mixture at a temperature in the range of from 1100° C. to 1300° C. thereby mainly forming a fired substance of a rare earth oxysulfide represented by the chemical formula, R 2 (1-x) Pr 2x O 2 S, washing said fired substance with an acid and water, and subjecting said washed material to hot isostatic pressing at a temperature of not less than 1400° C. under a pressure of not less than 100 MPa thereby forming a rare earth oxysulfide ceramic containing PO 4 in an amount not more than 15 ppm, wherein R stands for at least one member selected from the group consisting of Y, Gd, La and Lu and A for at least one member selected from the group consisting of Li, Na, K, Rb, and Cs, and x satisfies the expression, 1×10 -5 ≦x≦5×10 -2 .