X-ray phosphors and X-ray intensifying screen using the phosphor

An X-ray intensifying screen comprising:

• a support;
• and
• a phosphor layer supported on said support, said phosphor layer comprising a phosphor which emits light by the excitation of X-rays, having a composition represented by the formula:
• Ln.sub.1-x-(2/3)y-(1/3)z M".sub.y M'.sub.z DO.sub.4 :xR.sup.3+
• where:
• M" is at least one element selected from the group consisting of Ca, Sr and Cd,
• M' is at least one alkali metal selected from the group consisting of Li, Na and K,
• Ln is at least one rare earth element selected from the group consisting of Y, La and Lu,
• D is Ta, or Ta and Nb,
• R is at least one activator metal selected from the group consisting of Tm, Ce, Pr, Sm, Eu, Tb, Dy and Yb,
• y is a value in the range of 1.times.10.sup.-5 to 1,
• z is a value in the range of 1.times.10.sup.-4 to 0.1, and
• x is a value in the range of 0 to 0.05,
• said phosphor being obtained by admixing an oxide of Ln in an amount corresponding to 1-x-(2/3)y-(1/3)z parts by mol of Ln, an oxide of D in an amount corresponding to one part by mol of D, an oxide of R in an amount corresponding to x parts by mol of R, a chloride of M' in an amount sufficient to provide z parts by mol of M' and a carbonate of M" in an amount corresponding by y parts by mol of M", the amount of chloride of M' being larger than z parts by mole of M' in said phosphor and
• firing the admixture at a temperature and for a time sufficient to provide said phosphor having said composition and
• wherein said phosphor exhibits a smaller afterglow and a greater brightness intensity than the same phosphor absent M" and M'.