Experimental investigation of point defects and motion of charge in Al2O3, MgO, and SrO

This study investigates the electronic structure, motion of charge, and trapping mechanisms in Al2O3, MgO, and SrO. Thermochemically colored, electron irradiated, neutron irradiated, and gamma irradiated single crystals are studied from 6 to 3000K. A wide range of experimental techniques are used. For Al2O3, the excited state in F centers autoionizes at 6 K showing this state is in or very close to the conduction band. The Stoke's shift obtained from a photoluminescence band shape analysis does not predict the experimental emission peak energy of 3.0 eV but predicts 4.8 eV. This implies the emission occurs from a different state than the one excited into. In MgO, the sample dependent 2.3 eV phosphorescence near room temperature is directly related to the concentration of H- ions trapped in oxygen vacancies and is not related to the F center concentration. The H- ion is most likely responsible for the low temperature phosphorescence also. The F center interacts with the low-temperature electron trap at 100K showing the excited state is very near to the conduction band. A 0900K thermoluminescence peak in SrO produces F+ center emission which implies a bare oxygen vacancy may exist