Influence of Carbon Doping on Stability of Intrinsic Defects in Y₃Al₅O₁₂ and Lu₃Al₅O₁₂

Methods of crystal growth of rare earth garnets without precious metal crucibles are extensively developed nowadays. This work addresses defects forming in carbon‐containing Lu3Al5O12 crystals grown in Ar + CO atmosphere in W crucibles. The influence of carbon admixture on formation energies and oxidation states of intrinsic defects has been studied by ab initio calculations and optical spectroscopy. 21 types of isolated and complex defects have been considered in oxygen‐poor conditions of crystal growth in Ar + CO reducing atmosphere and oxygen‐rich conditions of postgrowth annealing of crystals in air. Despite the same type of crystalline structure and similar chemical compositions of Y3Al5O12 and Lu3Al5O12, the remarkable differences in formation mechanisms of color centers have been found in these materials. The conducted modeling suggests a reduced likelihood of the formation of positively charged carbon‐related defects responsible for color center formation, such as carbon occupying the oxygen site (CO) and interstitial carbon (Ci), in LuAG:C when compared to YAG:C. Regarding optical properties, fewer types of color centers are observed in LuAG:C absorption spectra, indicating a good agreement between simulation and experimental data. This study provides fresh insights into the mechanisms behind color center formation in rare earth garnets.