SYNTHESIS OF YAGCR PHOSPHORS BY PRECIPITATION FROM ALUMINUM AND YTTRIUM SULFATE-SOLUTIONS

Luminescent chromium doped yttrium aluminum garnet (YAG:Cr) powders we re prepared using yttrium and aluminum (hydrous) oxide precursor parti cles produced by precipitation from aqueous sulfate solutions in urea. The rate of precipitation of yttrium hydrous oxide particles was obse rved to be slower than that of the aluminum hydrous oxide particles in the two component solution (yttrium plus aluminum sulfate). However, as single components the yttrium hydroxide nucleation occurred at a fa ster rate. The pH of the single aluminum and yttrium sulfate solution must be greater-than-or-equal-to 2.9 and greater-than-or-equal-to 5.5, respectively for precipitation to occur. Precipitation in a two compo nent mixture is controlled by the acidic aluminum sulfate solution and homogeneous co-precipitation was not achieved. We have sped up the re action by seeding a yttrium sulfate solution with aluminum hydroxide p articles to promote rapid heterogenous nucleation of yttrium hydrous o xide. Heat treatment of the resulting precursor powders to 1200-degree s-C yielded YAG powders with some unreacted alumina and yttria.