ZnIn$_2$S$_4$ and ZnIn$_2$S$_4$ : Co single crystals crystallized in
rhombohedral forms with lattice constants a = 3.852 {|AA}, c =
37.215 {\AA} for ZnIn2S4 and a = 3.823 {\AA} and c = 36.975 {\AA}
for ZnIn$_2$S$_4$ : Co. The direct and indirect band ...
ZnIn$_2$S$_4$ and ZnIn$_2$S$_4$ : Co single crystals crystallized in
rhombohedral forms with lattice constants a = 3.852 {|AA}, c =
37.215 {\AA} for ZnIn2S4 and a = 3.823 {\AA} and c = 36.975 {\AA}
for ZnIn$_2$S$_4$ : Co. The direct and indirect band gaps were to be
2.895 and 2.741 eV for ZnIn$_2$S$_4$ and 2.392 and 2.268 eV for
ZnIn$_2$S$_4$ : Co at 4 K. The temperature dependence of the optical
energy gap was well represented by the Varshni equation. The values
of $\alpha$ for the direct and the indirect energy gaps were found
to be 4.504 $\times$ 10$^{-4}$ eV/K and 2.392 $\times$ 10$^{-4}$
eV/K, respectively, the ZnIn$_2$S$_4$, and the values of $\beta$
were found to be 35 K and 14 K. For ZnIn$_2$S$_4$ : Co, the values
of $\alpha$ for the direct and tje indirect energy gaps were given
by 2.741 $\times$ 10$^{-4}$ eV/K and 4.121 $\times$ 10$^{-4}$ eV/K
respectively, and the values of $\beta$ by 23 K and 31 K.