It was pointed out that the photo-induced and photo-transferred thermoluminescence of sapphire crystals suggested the existence of deep traps for charge carriers. These traps, which filled up under the influence of ionizing radiation, were not emptied by heating to up to 700K. Traps of both signs were present, and their concentrations were estimated to be of the order of 1017 to 1018/cm3. They were very stable, persisted for years, and annealed out at 1000K. It was proposed that, during the ionizing irradiation of sapphire crystals, a lattice defect of a new type might be created. It was suggested that this could be a quasi-atom, which had a self-trapped electron as its core; with an associated delocalized hole.

V.Flerov, A.Flerov: Materials Science Forum, 1997, 239-241, 757-60