Spin-orbit coupling effects in ${\mathrm{CdGa}}_2$${\mathrm{Se}}_4$:${\mathrm{Co}}^{2+}$ single crystals

Single crystals of ${\mathrm{CdGa}}_2$${\mathrm{Se}}_4$:${\mathrm{Co}}^{2+}$ were grown by the chemical transport reaction method using iodine as a transporting medium. The optical absorption peaks observed at 4132, 4332, 5970, 6329, 12 903, and 13 793 ${\mathrm{cm}}^{\mathrm{-}1}$ at 292 K can be explained in terms of the electronic transitions of ${\mathrm{Co}}^{2+}$ ion in $S_4$ symmetry. The crystal-field parameter Dq and the Racah parameter B were found to be 413 and 455 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively. Also the absorption spectrum of ${\mathrm{CdGa}}_2$${\mathrm{Se}}_4$:${\mathrm{Co}}^{2+}$ single crystals obtained at 77 K in the 700–800-nm region was analyzed using $S_4$ symmetry along with spin-orbit coupling effects.