Patent ID: 8529859

Claim:
A method of preparing a crystalline form of a compound of formula I: (A 1−n Y n ) 5 (PO 4 ) 3 X (I) wherein A is selected from the group consisting of Ca, Sr and Ba, Y is a dopant selected from the group consisting of Yb, Nd, Ce, Cr, Tm, Ho, Er, and Sm, subscript n is from 0 to about 0.1, and X is selected from the group consisting of F, Cl and OH, the method comprising: dissolving the compound of formula I in an aqueous solution comprising an acid, wherein the solution is at a temperature of from about 0 to about 100° C.; and forming a supersaturated solution of the compound of formula I, thereby preparing the crystalline form of the compound of formula I.