X-ray intensifying screen based on rare earth tantalate

Process for preparing the phosphor having the monoclinic M' structure and selected from the group consisting of:

• (a) YNb.sub.x Ta.sub.1-x O.sub.4, where x is 0 to about 0.15;
• (b) LuNb.sub.x Ta.sub.1-x O.sub.4, where x is 0 to about 0.2;
• (c) Y.sub.1-y Tm.sub.y TaO.sub.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.sub.1-y Tb.sub.y TaO.sub.4, where y is about 0.001 to about 0.15;
• (g) Lu.sub.1-y Tb.sub.y TaO.sub.4, where y is about 0.001 to about 0.15;
• (h) Gd.sub.1-y Tb.sub.y TaO.sub.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 and a flux selected from the group consisting of Li.sub.2 SO.sub.4, LiCl and a BaCl.sub.2 /LiCl eutectic mixture, the weight of the flux being 1/5 to 1/2 of the total weight of the mixture;
• (b) firing the resultant mixture in an inert container at about 1100.degree. C. to less than about 1450.degree. C. for at least about 4 hours;
• and
• (c) recovering the phosphor.

An X-ray intensifying screen comprising a phosphor-binder coating upon a flexible support wherein the phosphor is comprised of colorless single-phase particles having a surface area of about 0.075 to 0.300 m.sup.2 /g, a particle size of about 3 to 10 .mu.m, the monoclinic M' structure and selected from the group consisting of:

• (a) YNb.sub.x Ta.sub.1-x O.sub.4, where x is 0 to about 0.15;
• (b) LuNb.sub.x Ta.sub.1-x O.sub.4, where x is 0 to about 0.2;
• (c) Y.sub.1-y Tm.sub.y TaO.sub.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.sub.1-y Tb.sub.y TaO.sub.4, where y is about 0.001 to about 0.15;
• (g) Lu.sub.1-y Tb.sub.y TaO.sub.4, where y is about 0.001 to about 0.15;
• (h) Gd.sub.1-y Tb.sub.y TaO.sub.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.