Single crystals of Zn& "Cd"Ga2Se4 and Zn& "Cd"Ga2Se4. Co'+ were grown by a chemical-transport reaction method using the ingots synthesized with 3 at. % excess of selenium as starting materials. It has been found that these single crystals have a defect chalcopyrite structure, and the tetragonal distortion factor {2c/a) decreases due to the introduction of an excess of selenium. It has also been shown that these compounds have a direct optical-energy gap, and the direct optical-energy gap decreases when a composition X increases and when a cobalt impurity is introduced. The temperature dependence of the optical-energy gap is well given by the Varshni equation.Impurity optical absorption of the Zn& "Cd Ga&Se4.Co + single crystals has been investigated in the temperatures 289 and 80 K and in the wavelength region 250-2500 nm. It is concluded that a cobalt atom in the Zn& "Cd"Ga2Se4. Co'+ single crystals with a small tetragonal distortion occupies nearly a cubic Td symmetry site of the host lattice as a Co + ion; then the observed impurity optical-absorption peaks are attributed to the electronic transition between the energy levels of a Co + ion in a crystal field of a cubic Td symmetry.
BiSeI and BiSe1:Co single crystals were grown by the vertical Bridgman technique using the ingots synthesized from the mixtures with the excess iodine of 8.6 mol%. The grown single crystals crystallized in the orthorhombic structure. The optical energy gap with the indirect band structure was 1.28 eV and 1.25 eV at 293 K for BiSeI and BiSeI:Co (2 1110196) single crystal. The impurity optical absorption peaks by the cobalt doped in the BiSeI single crystal were observed. These peaks are identified to the electron transitions between the energy levels of Co" ion or Co" ion sited at the T, symmetry point.
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