ESR study of Ce3+ ions in a CaGa2S4 single crystal

ESR measurements have been carried out to determine the local environment and the ground state of Ce3+ ions in the orthorhombic CaGa2S4 at 4.2 K. More than 30 ESR lines are observed with almost the same angular dependence. The local symmetry and the anisotropic g-tensor for the four strongest ESR signals indicate that Ce3+ ions substitute the three independent Ca sites. A part of Ce3+ ions at the Ca2+ sites and a neighbouring sulphur vacancy are expected to form complex centers in view of the other weak ESR lines observed. The ground state of Ce3+ in the host lattice is shown to consist of mostly phi (1/2) by fitting the ESR spectra using the spin Hamiltonian. The upper F-2(7/2) state is thought to be slightly mixed into the ground state F-2(5/2) judging from a small difference in the fitting.