Optical absorption and electrical conduction in KBr crystals containing diffused magnesium

The conductivity of KBr crystals containing diffused magnesium is smaller in the free vacancy conduction region II (where the conductivity is due to the cation vacancies present in the crystal as a result of the presence of divalent cation impurities, and all the vacancies are in the free state) than in a pure crystal. These crystals shown an optical absorption band peaking at 228 nm. It is suggested that the decrease in the conductivity and the 228 nm band are associated with the reduction of background divalent cations like Pb2+ to mono- or zero-valent form and formation of U centres, respectively.