Photoconversion of F+ centers in neutron-irradiated MgO

In neutron-irradiated MgO crystals, experiments and theory demonstrate that photon excitation of the positively charged anion vacancies (F+ centers) a t 5.0 eV releases holes that are subsequently trapped at V-type centers, wh ich are cation vacancies charge-compensated by impurities, such as Al3+, F, and OH ions. A photoconversion mechanism occurs very likely via electron t ransfer to F+ centers from the quasi-local states which are induced in the valence band. INDO quantum chemical simulations of Fi centers confirmed the appearance of two induced quasi-local states located at 1.2 and 2.0 eV bel ow the top of the valence band. (C) 2000 Elsevier Science B.V. All rights r eserved.