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

Optical absorption spectra measured in as‐grown and gamma‐ray irradiated un‐doped YAG, Li‐doped YAG, and Ca‐doped YAG single crystals are compared for characterization of effects introduced by impurities. The studies are conducted on single crystals grown by the vertical Bridgman method. Basing on the Li+ incorporation mechanism, clarification is done regarding the optimal amounts of Li+ for preparation of YAG:Li crystals with low concentration of anion vacancies and related defects giving rise to absorption in the UV range. Differences in behavior are recorded in variously doped crystals subjected to gamma‐ray irradiation; in comparison to un‐doped YAG, the induced absorption coefficient in Li‐doped YAG of optimal composition is lower more than six times. High transmission in the UV and high radiation tolerance are important for most applications of YAG, especially when operated in high radiation fields. High transmission and high radiation hardness are the most demanding parameters for YAG single crystals, when operating in high radiation fields. Li+ dopant is efficient for the preparation of crystals with low concentration of anion vacancies and related F‐type centers, and of O− centers. In comparison to un‐doped YAG, the radiation induced absorption in the UV range in Li‐doped YAG is significantly lower.