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

Optical spectroscopy and theory demonstrate that photon excitation of the positively charged anion vacancies (F⁺ centers) at 5.0 eV in neutron-irradiated MgO crystals releases holes that are subsequently trapped at V-type centers, which are cation vacancies charge compensated by impurities, such as Al³⁺, F^-, and OH^- 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⁺ center serves to release a hole to the V-type centers and subsequently trap a hole from an Fe³⁺ ion. The net effect was the increase of V-type centers mostly at the expense of Fe³⁺ ions. It was also shown that concurrently there was a component which distributed holes directly from Fe³⁺ to the V-type centers.