Patent ID: 7138074

Claim:
A process for preparation of a stimulable phosphor represented by the formula (I): Lu x Y y Gd z SiO p :a A, b L (I) in which A is at least one element selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb; L is at one element selected from the group consisting of Zr, Nb, Hf, Ta, Sn, Sm, Tm and Yb, provided that L differs from A; x, y and z are numbers satisfying the conditions of 0≦x, 0≦y, 0≦z and 1.5≦x+y+Z≦2.2; p is a number to neutralize the phosphor in regard to electric charge thereof, a is a number satisfying the condition of 2×10 −5 <a<6×10 −2 , and b is a number satisfying the condition of 0≦b<1×10 −2 , in which the stimulable phosphor absorbs and stores a portion of energy of radiation or ultraviolet rays when it is exposed to the radiation or ultraviolet rays, and emits stimulated light in a visible wavelength region when exposed to electromagnetic waves; which comprises the steps of: (1) heating a rare earth carboxylate represented by the formula (II) (R 1 —COO) 3 M.mH 2 O (II) in which M is at least one rare earth element selected from the group consisting of Lu, Y and Gd; R 1 is an aliphatic hydrocarbon group having 1 to 4 carbon atoms which has a substituent or no substituent; and m is a number satisfying the condition of 0≦m≦4; with an alkoxyalcohol represented by the formula (III), to obtain a solution: R 2 —O—(CH 2 ) n OH (III) in which R 2 is an aliphatic hydrocarbon group having 1 to 4 carbon atoms or a substituted aliphatic hydrocarbon group having 3 to 6 carbon atoms; and n is 2 or 3; (2) adding to the obtained solution a silicon alkoxide represented by the formula (IV): Si(OR 3 ) 4 (IV) in which R 3 is an aliphatic hydrocarbon group having 1 to 4 carbon atoms and a compound containing the element represented by A, and if required a compound containing the element represented by L, to prepare a mixture; (3) bringing water into contact with the prepared mixture to give a gel; and (4) subjecting the given gel to thermal decomposition under slightly reductive atmosphere.