Structural and Optical Properties of Cd1-xCoxGa2Se4 (0.0 ≤ x ≤ 1.0) Mixed Crystals

The structural and optical properties of Cd1-xCoxGa2Se4 mixed crystals were investigated in the range 0.0 ≤ x ≤ 1.0 by measuring the X-ray diffraction and optical absorption. The X-ray diffraction analysis demonstrated that Cd1-xCoxGa2Se4 crystalized into a tetragonal structure for 0.0 ≤ x ≤ 1.0. The tetragonal lattice constants were a = 5.744 Å and c = 10.784 Å for CdGa2Se4 (x = 0.0), and a = 5.611 Å and c = 10.913 Å for CoGa2Se4 (x = 1.0), which are the end members of the Cd1-xCoxGa2Se4 system, exhibiting a composition dependence that varied linearly with composition x. The tetragonal structural properties of Cd1-xCoxGa2Se4 were investigated by taking into account the compositional dependence of the tetragonal distortion, 2-(c/a), and bonding distances RCd(Co)-Se and RGa-Se. The optical absorption spectra exhibited triplet absorption bands in the range 650 900 nm corresponding to the A2(F) → 4 T1(P) transition of the Co ions with Td symmetry sites, and a broad band in the range 1100 2200 nm corresponding to the A2(F) → T1(F) transition, for all investigated compositions. The composition dependencies of the crystal-field parameter, Dq, and Racah parameter, B, are discussed on the basis of a tetrahedral crystal-field approximation and composition dependent tetragonal structure.