Colour centres in electron irradiated mgo

Abstract

Oxygen ion vacancies, which absorb light at 250 nm, are observed in 'pure' mgo after irradiation with 0.23-29 mev electrons. The threshold energy for anion vacancy formation is observed to occur at 0.33 mev; this corresponds to a displacement energy t_d=60 ev. Energy independent damage is observed below the threshold energy. Zero phonon lines are observed at wavelengths of 361.5, 1044.5 and 1342.5 nm in crystals irradiated at electron energies greater than 1.6 mev. Optical bleaching experiments suggest that these lines are associated with trapped electron centres. The energy dependence of the growth rate of the 1044.5 nm line confirms that intrinsic defect aggregates are involved, anion divacancies being the most probable.