X-ray intensifying screen based on rare earth tantalate

Claim 1

Process for preparing the phosphor having the monoclinic M' structure and selected from the group consisting of: (a) YNb x Ta 1-x O 4 , where x is 0 to about 0.15; (b) LuNb x Ta 1-x O 4 , where x is 0 to about 0.2; (c) Y 1-y Tm y TaO 4 , where y is 0 to about 0.03; (d) a solid solution of (a) and (b); (e) a solid solution of (a) and (c); (f) Y 1-y Tb y TaO 4 , where y is about 0.001 to about 0.15; (g) Lu 1-y Tb y TaO 4 , where y is about 0.001 to about 0.15; (h) Gd 1-y Tb y TaO 4 , where y is about 0.001 to about 0.15; (i) a solid solution of at least two of (f), (g) and (h); (j) any of (a) to (i) wherein up to 45 mole percent of the yttrium, lutetium or gadolinium is replaced by lanthanum; (k) any of (a) to (i) wherein up to 15 mole percent of the yttrium, lutetium or gadolinium is replaced by ytterbium; and (l) any of (a), (b), (c), (d) and (e) wherein up to 15 mole percent of the yttrium or lutetium is replaced by gadolinium, which process comprises the steps: (a) intimately mixing stoichiometric quantities of appropriate precursor oxides; (b) prefiring the resultant mixture in air in an inert container at about 1000° C. to about 1200° C. for about 10 to about 14 hours; (c) mixing the resultant prefired mixture with a flux selected from the group consisting of Li 2 SO 4 , LiCl and a BaCl 2 /LiCl eutectic mixture, the weight of the flux being 1/5 to 1/2 of the total weight of the mixture; (d) firing the flux-containing mixture in an inert container at about 1100° C. to less than about 1450° C. for at least about 3 hours; and (e) recovering the phosphor. (e) recovering the phosphor.