Optical absorption of MgGa 2Se 4:Ni 2+ single crystals

Abstract

Optical absorption of MgGa 2Se 4:Ni 2+ single crystals have been investigated in the visible and near-infrared region. We observed optical absorption peaks at 4597, 5807, 8779, 10416, 11876 and 11936 cm −1 due to nickel impurity and at 9088 cm −1 due to phonon of MgGa 2Se 4. The three absorption bands at 4597, 8779 and 11876 cm −1 among them are attributed to the crystal field transitions between the ground state 3 T 1( F) and the excited states 3 T 2( F), 3 A 2( F) and 3 T 1( P) of Ni 2+ ion with T d symmetry of MgGa 2Se 4 host. On the other hand, the two absorption bands at 5807 and 10416 cm −1 are assigned to the charge-transfer transitions of Ni 3+ + hv → Ni 2+( 3T 1(F)) + hole and Ni 3+ + hv → Ni 2+ ( 3T 2(F)) + hole , respectively. The shoulder structure at 11936 cm −1 is also ascribed to the charge-transfer transition of Ni 2+ ( 3T 1(F)) + hv → Ni 3+ + electron. From the optical absorption results, the energy levels of Ni 2+ ion are deduced and illustrated schematically relative to the band edges of MgGa 2Se 4.