Structural and Optical Properties of alpha-CoGa2S4 Crystals

다국어 초록 (Multilingual Abstract)

The structural and the optical properties of
$\alpha$-CoGa$_{2}$S$_{4}$ crystals, which were prepared by using
the melt technique, were investigated by using X-ray powder
diffraction and optical absorption. The crystal structure was a
tetragonal $\alpha$-phase with a tetragonal distortion of {\it
c}/{\it a} = 1.998 and an atomic coordinate of {\it u} = 0.2504.
The optical energy gap was found to be 1.89 eV at 300 K. We also
observed several absorption bands in the visible and the infrared
regions due to Co$^{2+}$ ions in the sublattice of
$\alpha$-CoGa$_{2}$S$_{4}$. The absorption bands were assigned to
electronic transitions between the energy levels of Co$^{2+}$ ions
with the T$_{d}$ symmetry of the host lattice along with
spin-orbit coupling. The crystal-field and the spin-orbit coupling
parameters were given by Dq = 404 cm$^{-1}$ and $\lambda$ = $-$308
cm$^{-1}$, respectively.