Optical spectroscopy and optimal crystal growth of some Cr4+-doped garnets

This paper describes the growth of single crystals of Cr4+-doped Y3Ga5O12 ( YGG) and Y3Al5O12 (YAG). Control of melt composition and post-growth anneal ing yields material that contains optimal concentrations of Cr4+ ions in di storted tetrahedral sites normally occupied by Ga3+ ions in YGG and Al3+ io ns in YAG. Both Cr4+-doped garnets exhibit strong visible and near-infrared absorption bands with peak cross sections of order 10(-18)-10(-19) cm(2) a nd emit into vibronically broadened but weakly allowed B-3(2) (T-3(2)) --> B-3(1) ((3)A(2)) transitions. Nonradiative decay is more efficient in YGG t han in YAG as a consequence of the slightly reduced energy gap against radi ative decay in the Ga-based garnet.