Photoconversion and dynamic hole recycling process in anion vacancies in neutron-irradiated MgO crystals

Abstract

Optical spectroscopy and theory demonstrate that photon excitation of the positively charged anion vacancies (F{sup +} centers) at 5.0 eV in neutron-irradiated MgO crystals releases holes that are subsequently trapped at {ital V}-type centers, which are cation vacancies charge compensated by impurities, such as Al{sup 3+}, F{sup {minus}}, and OH{sup {minus}} ions. The concentration of trapped-hole centers was found to exceed that of available anion vacancies. The disproportionately large amount of holes produced is attributed to a dynamic recycling process, by which the F{sup +} center serves to release a hole to the {ital V}-type centers and subsequently trap a hole from an Fe{sup 3+} ion. The net effect was the increase of {ital V}-type centers mostly at the expense of Fe{sup 3+} ions. It was also shown that concurrently there was a component which distributed holes directly from Fe{sup 3+} to the {ital V}-type centers. {copyright} {ital 1999} {ital The American Physical Society}