Photoconversion of<i>F</i>-type centers in thermochemically reduced MgO single crystals

Abstract

Optical absorption and luminescence experiments were used to study the photoconversion of neutral oxygen vacancies (F centers) in MgO single crystals thermochemically reduced at elevated temperatures. In crystals with an undetectable concentration of hydride ions and a moderate concentration of F centers $(\ensuremath{\approx}{10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}),$ excitation with UV-light produces positively charged anion vacancies ${(F}^{+}$ centers) and electrons which are subsequently trapped at impurities. Under continuous excitation, the ${F}^{+}$ centers release holes which are trapped at cation vacancies charge compensated by impurities. In crystals with high concentrations of both hydride ions and F centers $(\ensuremath{\approx}{10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}),$ the electrons from the F to ${F}^{+}$ photoconversion are trapped mainly at the hydride ions to form ${\mathrm{H}}^{2\ensuremath{-}}$ ions, which are metastable at room temperature.