Polycrystals of ${\mathrm{ZnGa}}_2$${\mathrm{S}}_4$ and ${\mathrm{ZnGa}}_2$${\mathrm{S}}_4$:${\mathrm{Co}}^{2+}$ were prepared from high-purity elements at 1270 °C. The optical-absorption spectra of these polycrystalline powders were measured in the wavelength region 300–3000 nm with use of an integrating sphere and photoacoustic spectrophotometer at 298 K. The optical energy gap is found to be 3.18 eV for the ${\mathrm{ZnGa}}_2$${\mathrm{S}}_4$ crystal and 2.60 eV for the ${\mathrm{ZnGa}}_2$${\mathrm{S}}_4$:${\mathrm{Co}}^{2+}$ crystal. The optical-absorption peaks in the measurement of ${\mathrm{ZnGa}}_2$${\mathrm{S}}_4$:${\mathrm{Co}}^{2+}$ crystal absorption spectrum at 3790, 6049, 13 725, 20 704, and 22 779 ${\mathrm{cm}}^{\mathrm{-}1}$ are found to be the electron transition of the ${\mathrm{Co}}^{2+}$ ion with ${\mathit{T}}_{\mathit{d}}$ symmetry from the ground state ${}_{}{}^4{}_{}{}^{}$${\mathit{A}}_2$${(}^4$F) to the excited states ${}_{}{}^4{}_{}{}^{}$${\mathit{T}}_2$${(}^4$F), ${}_{}{}^4{}_{}{}^{}$${\mathit{T}}_1$${(}^4$F), ${}_{}{}^4{}_{}{}^{}$${\mathit{T}}_1$${(}^4$P), ${}_{}{}^2{}_{}{}^{}$${\mathit{T}}_2$${(}^2$G), and ${}_{}{}^2{}_{}{}^{}$E${(}^2$G). The crystal-field parameter and the Racah parameter, which were obtained from the optical-absorption peaks, are found to be Dq=379 ${\mathrm{cm}}^{\mathrm{-}1}$ and B=560 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively. The ${}_{}{}^4{}_{}{}^{}$${\mathit{T}}_1$${(}^4$P) state of the ${\mathrm{Co}}^{2+}$ ion splits into three state of ${\mathrm{\Gamma }}_6$, ${\mathrm{\Gamma }}_8$, and ${\mathrm{\Gamma }}_8$+${\mathrm{\Gamma }}_7$ by first-order spin-orbit coupling effects at 298 K. The value of the spin-orbit coupling parameter was λ=-436 ${\mathrm{cm}}^{\mathrm{-}1}$.

• Received 10 October 1989

DOI:https://doi.org/10.1103/PhysRevB.41.8541