Optical spectroscopy and theory indicated that photon-excitation of positively charged anion vacancies (F+ centers) at 5eV, in neutron-irradiated crystals, should release holes that were then trapped at V-type centers. The latter were cation vacancies that were 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 disproportionate number of holes which was produced was attributed to a dynamic recycling process in which the F+ center released a hole to the V-type centers and then trapped a hole from an Fe3+ ion. The net effect was an increase in V-type centers; mainly at the expense of Fe3+ ions. It was also shown that there was a simultaneous component which distributed holes directly from Fe3+ to V-type centers.

Photoconversion and Dynamic Hole Recycling Process in Anion Vacancies in Neutron-Irradiated MgO Crystals. M.A.Monge, R.González, J.E.Muñoz Santiuste, R.Pareja, Y.Chen, E.A.Kotomin, A.I.Popov: Physical Review B, 1999, 60[6], 3787-91