Optical and electrical properties of some sulphates doped with cobalt

Doubly ionized cobalt ion which has a 4F ground state exhibits several optical bands in orthorhombic sulphates. In view of the low symmetry, many degenerate states split and at low temperature (77°K) well resolved bands have been observed which enable the detailed calculation of the crystal field parameters in orthorhombic symmetry. Electrical conductivity measurements in pure potassium and ammonium sulphates show only the extrinsic unassociated region while in cobalt doped crystals, extrinsic as well as association regions are observed. Three distinct regions with slopes 0·86, 1·2 and 0·5 eV are obtained in cobalt doped K2SO4. X-irradiated pure crystals give two prominent bands at 2200 and 3300 Å which are attributed to SO3- and SO2-. Divalent cobalt doped crystals give additional bands at 2100 and 3100 Å. These bands are attributed to Co+ in different surroundings. Three ESR lines with 'g' values 2·042, 2·02 and 2·004 are obtained in support of the assignments. © 1973.