Phosphors and methods of preparing the same

An infrared stimulable phosphor consisting essentially of:

• (a) an alkaline earth sulfur selenium crystalline matrix the alkaline-earth metal selected from the group consisting of strontium, calcium and combinations thereof, wherein the molar ratio of S to Se is between about 1:10 and 10:1;
• (b) Eu as a first activator in an amount of about 5 to about 500 ppm by weight based on the weight of the matrix;
• and
• (c) Bi, Sm or combinations thereof, as a second activator each in an amount of about 5 to about 500 ppm by weight based on the weight of the matrix,
• said activators being dispersed within said matrix, said matrix and said activators cooperatively defining active sites adapted to store energy upon exposure of the phosphor to visible or ultraviolet light, said active sites being adapted to emit said stored energy as visible light upon exposure of the phosphor to infrared light, said phosphor including at least about 5.times.10.sup.17 of said active sites per cm.sup.3 and having a stimulation quantum efficiency of at least 5 percent.