Optical Properties of $Zn_2AgGaSe_4$ and $Zn_2AgGaSe_4 : Co^{2+}$ Crystals

Abstract

Optical properties of Zn2AgGaSe4 and Zn2AgGaSe4: Co crystals are investigated in the visible and near-infrared regions at 298 K. The direct band gap at 298 K is 1.630 eV for the Zn2AgGaSe4 and 1.567 eV for the Zn2AgGaSe4: Co crystals, respectively. In the optical absorption and photoacoustic (PA) spectra of the Zn2AgGaSe4: Co, we observed five impurity absorption peaks at 4220, 5952, 12 422, 12 987 and 14 184 cm-1. These impurity absorption peaks are attributed to the electronic transitions between the split energy levels of Co2+ ions with T(d) symmetry of Zn2AgGaSe4 host lattice. The crystal field parameter Dq, the Racah parameter B, and the spin-orbit coupling parameter-lambda are given by 422, 425 and -440 cm-1, respectively.