Optical properties of Ga 2Se 3:Co 2+ single crystals

Abstract

Optical absorption of Ga 2Se 3:CO 2+ single crystals grown by the Bridgman technique has been investigated in the region of the fundamental absorption edge and the near-infrared over the temperature range 20–300 K. The direct band gap of the undoped Ga 2Se 3 single crystals is 1.92 eV at room temperature. The direct band gap of the Co-doped Ga 2Se 3 is decreased with a increasing concentration of Co-dopant, and then that of the 3.5 mole % Co-doped Ga 2Se 3 is given by 1.40 eV. The temperature dependence of the optical energy gaps is well explained by the Varshni equation. We observed three impurity absorption peaks at 4032, 6184, and 13831 cm −1 in the absorption spectrum of the Ga 2Se 3:Co 2+ (0.1 mole %) single crystals. We can see that these impurity absorption peaks are assigned to the allowed electron transitions from the ground state 4 A 2( 4 F) to the excited states 4 T 2( 4 F), 4 T 1( 4 F), and 4 T 1( 4 P) of Co 2+ ions in T d symmetry of Ga 2Se 3 host lattice. The crystal field parameter Dq and the Racah parameter B are given by 403 and 503 cm −1, respectively.