An optical and MCD-ODMR study of the Co2+ ion in LiGa5O8

Optical and magnetic-circular-dichroism-optically-detected-magnetic-resonance studies have been carried out on Co-doped LiGa5O8. The Co ions are found to be predominantly in the 2+ charge state and to substitute for tetrahedrally coordinated Ga3+ in the LiGa5O8 lattice, in sites which are shown to have C3 point-group symmetry. The strong absorption bands from the ground state 4A2(4F) to the excited states 4T1(4P) and 4T1(4F) are each split by the low-symmetry C3 field. A combination of the low-symmetry field and spin-orbit coupling is responsible for the ground-state splitting of 19.5 + - 0.5 cm-1 observed by fluorescence line narrowing. Strong broadband luminescence is observed from the 4T1(4P) level to three lower levels, 4A2(4F), 4T2(4F), and 4T1(4F), with a lifetime that is constant at 200 ns from 10 K up to room temperature. The optically-detected magnetic-resonance studies show that the Co2+ ions are in sites which have axial symmetry along -type axes of the unit cell, indicative of the C3 symmetry present in these substitutional sites. We give a detailed crystal-field model for the Co2+ ion in the C3 site in LiGa5O8 and deduce the crystal-field parameters from our experimental data.