A Experimental Investigation of Point Defects and Motion of Charge in Aluminum Oxide, Magnesium Oxide, and Strontium Oxide
Scope of Study. The object of this study is to investigate the electronic structure, motion of charge, and trapping mechanisms in aluminum oxide, MgO, and SrO. Thermochemically colored, electron irradiated, neutron irradiated, and gamma irradiated single crystals are studied from 6 K to 300 K. A wide range of experimental techniques are used. Findings and Conclusions. For aluminum oxide, 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. Analysis shows a strong electron-lattice interaction. Interconversion between the 6.1 and the 4.8 and 5.4 eV absorption bands occurs at 6 K. A thermoluminescence peak at 260 K is responsible for this. It is believed a H- ion is the responsible electron trap. 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 concentation. The H- ion is most likely responsible for the low temperature phosphorescence also. The F center interacts with the low temperature electron trap at 10 K showing the excited state is very near to the conduction band. It appears photoconductivity associated with the F+ center is seen starting at 80 K. A 90 K thermoluminescence peak in SrO produces F+ center emission which implies a bare oxygen vacancy may exist.
- Pub Date:
- COLOR CENTER;
- F CENTER;
- Physics: Condensed Matter