gems, corundum, treatments.6, irradiation, α-Al2O3, anion Frenkel defects, diffusion-controlled reactions, fast neutrons, optical absorption, thermal annealing

Corundum (α-Al₂O₃) is a technologically important material and, in particular, is widely used in optical applications such as luminescent radiation dosimeters and cryogenic scintillators, and is being considered as a promising candidate for windows in future fusion reactors. Its optical and mechanical properties are controlled by the presence of radiation-induced defects, particularly those produced by fast neutrons. Herein, the thermal stability and recombination kinetics of primary anion Frenkel defects—the F and F⁺ electronic centers and oxygen interstitials—in fast-neutron-irradiated α-Al₂O₃ single crystals are analyzed. Theory is developed considering the formation of both neutral and charged oxygen Frenkel defect pairs, as well as defect migration, interaction, and recombination. Based on ab initio calculations and a new theoretical kinetics analysis, the coexistence is demonstrated for the first time, in comparable concentrations, of two interstitial types—neutral O atoms and negatively charged O⁻ ions (with attributed optical absorption band maxima at 6.5 eV and 5.6 eV, respectively)—and their diffusion parameters, necessary for the prediction of secondary defect-induced reactions and defect/material thermal stability, are obtained.