Abstract
Optical properties of Zn 2AgGaSe 4 and Zn 2AgGaSe 4: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 Zn 2AgGaSe 4 and 1.567 eV for the Zn 2AgGaSe 4:Co crystals, respectively. In the optical absorption and photoacoustic (PA) spectra of the Zn 2AgGaSe 4: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 Co 2+ ions with T d symmetry of Zn 2AgGaSe 4 host lattice. The crystal field parameter Dq, the Racah parameter B, and the spin-orbit coupling parameter λ are given by 422, 425 and −440 cm −1, respectively.
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