Interstitial Li$^+$ Controls the UV Transmission and the Radiation Hardness in YAG

Optical absorption spectra measured in as-grown and gamma-ray irradiatedun-doped YAG, Li-doped YAG, and Ca-doped YAG single crystals arecompared for characterization of effects introduced by impurities. The studiesare conducted on single crystals grown by the vertical Bridgman method.Basing on the Li$^+$ incorporation mechanism, clarification is done regardingthe optimal amounts of Li$^+$ for preparation of YAG:Li crystals with lowconcentration of anion vacancies and related defects giving rise to absorptionin the UV range. Differences in behavior are recorded in variously dopedcrystals subjected to gamma-ray irradiation; in comparison to un-doped YAG,the induced absorption coefficient in Li-doped YAG of optimal composition islower more than six times. High transmission in the UV and high radiationtolerance are important for most applications of YAG, especially whenoperated in high radiation fields.