Composition dependence of the structural and the optical properties of Cd1-xMnxGa2S4 mixed crystals

The composition dependence of the structural and the optical properties of Cd1-xMnxGa2S4 mixed crystals prepared by using the melt technique was investigated in the region of 0.00 less than or equal to x less than or equal to 1.00 by using X-ray powder diffraction and optical absorption measurements. An analysis of the X-ray powder diffraction spectra showed that the crystals in the region of 0.00 less than or equal to x less than or equal to 0.67 crystallized into a defect chalcopyrite structure and in the region of 0.90 less than or equal to x less than or equal to 1.00 crystallized into an orthorhombic structure. In the region of 0.67 < x < 0.90, a miscibility gap existed. The lattice constants showed a linear variation with composition x in the corresponding regions. We observed two absorption bands, 2.52 and 2.68 eV, near the fundamental absorption edge of the optical absorption spectra at 300 K. These absorption bands were assigned to the transitions (6)A(1) (S-6) --> T-4(2) ((4)G) and (6)A(1) (S-6) --> E-4((4)G) of Mn2+ ions. We also observed the composition dependence of the optical energy gaps,with an abrupt and downward bowing for the region of 0.00 less than or equal to x less than or equal to 0.67 and a linear variation for the region of 0.90 less than or equal to x less than or equal to 1.00. This anomalous dependence was related to a peculiar behavior of the manganese transition metals in the Cd1-xMnxGa2S4 system.