Electronic excitations, luminescence and lattice defect formation in α-al₂O₃ crystals

Abstract

We review studies of the effects of electronic excitation in α-Al₂O₃ crystals, paying special attention to the problem of the existence of self-trapped excitons and self-trapped holes in the material. After a brief review on the crystallographic and electronic structures, information on thermal and radiation-induced defects is summarized. The concept of self-trapping of holes is critically reviewed and the possible contribution of the native acceptor impurities in the processes which have been attributed to the self-trapped holes is discussed. Experimental observations on the so-called intrinsic luminescence in α-Al₂O₃ crystals is surveyed and again the possible contribution of native impurities is discussed. The relaxation processes of electronic excitation in α-Al₂O₃ crystals are compared with those in MgO and SiO₂ having similar physical and chemical properties but differeing in the crystallographic and electronic structures. The properties of metastable defects induced by electronic excitation are discussed in connection with the recently discovered transient volume expansion effect under the excitation by short electron pulses.

Key Words:

• Al₂O₃
• luminescence
• electronic excitations
• lattice defect formation
• self-trapping