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 ${(F}^{+}$ 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 ${\mathrm{Al}}^{3+},$ ${\mathrm{F}}^{\ensuremath{-}},$ and ${\mathrm{OH}}^{\ensuremath{-}}$ 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 ${\mathrm{Fe}}^{3+}$ ion. The net effect was the increase of V-type centers mostly at the expense of ${\mathrm{Fe}}^{3+}$ ions. It was also shown that concurrently there was a component which distributed holes directly from ${\mathrm{Fe}}^{3+}$ to the V-type centers.