Novel rare-earth doped fluorides compositions

A process comprising combining an aqueous solution of an ammonium fluoride or hydrogen fluoride, or mixtures thereof, with one or more aqueous solutions of the salts of at least two alkaline earth metals, and an aqueous solution of a salt comprising a 3-valent rare earth metal cation, the amount of the rare-earth metal cation being in the range of 0.5 to 20 mol-% of the molar concentration of the total alkaline earth metal cation content, thereby forming a reaction mixture from which is formed a precipitate of a rare-earth doped solid state solution of alkaline earth fluorides represented by the formula

• REx(CaaSrbBac)1−xF2+x−2yOy
• wherein RE represents a three-valent rare-earth element, 0.005≦×≦0.20, and 0≦y≦0.2, a+b+c=1, with the proviso at least two of a, b, and c are not equal to zero;
• the rare-earth doped multi-valent metal fluoride being characterized by an aqueous solubility of less than 0.1 g/100 g of water.

A process comprising heating in the presence of oxygen a composition comprising a rare-earth-doped solid-state solution of alkaline earth fluorides represented by the chemical formula

• REx(CaaSrbBac)1−xF2+x−2yOy
• wherein RE represents a three-valent rare-earth element, 0.005≦×≦0.20, and 0≦y≦0.2, a+b+c=1, with the proviso at least two of a, b, and c are not equal to zero;
• to a maximum temperature in the range of 200° C. to 1000° C., followed by cooling, with the proviso that the composition so heated has not previously been exposed to the maximum temperature.