OPTICAL-PROPERTIES OF UNDOPED AND CO-DOPED HGIN2SE4 CRYSTALS

We have investigated the optical properties of undoped and Go-doped KgIn(2)Se(4) crystals. It has been found that the compound HgIn2Se4 has a direct band gap of 1.16 eV at 298 K and a defect chalcopyrite structure with the tetragonal distortion c/a = 2.02. It has been observed that the doping of the HgIn2Se4 with cobalt introduces a red shift of the absorption edge by about 60 meV due to the formation of a solid solution between the cobalt compounds with a smaller band gap and the host compound. It has also been identified that cobalt-transition ions in the HgIn2Se4 occupy the cubic T-d symmetry sites of the host lattice as Co2+. We have observed weak and broad absorption bands in the near-infrared regions corresponding to the transition (4)A(2)(F-4)-->T-4(1)(F-4) of Co2+. The observed absorption bands have been analyzed in terms of the crystal-field theory along with the spin-orbit coupling interaction.