Effects of Fe-ion irradiation and annealing on the optical absorption in sapphire

We have studied the optical absorption in sapphire after Fe-ion irradiation and subsequent vacuum heat treatment. The absorption parameters and the nature of the transitions between localized states and allowed bands have been shown to be influenced by substitutional defects, intrinsic radiation-induced defects, and their complexes. We have evaluated the contributions of individual substitutional defects, their clusters, and complexes of substitutional defects with native vacancies and the effect of the iron oxides forming during annealing on the absorption in sapphire. The nature of the substitutional defect clusters and impurity-native defect complexes has been analyzed in detail.