Optical spectroscopy of Ce3+ in BaLiF3

The optical absorption spectrum of Ce3+ in BaLiF3 crystals consists of seve ral overlapping broad bands. The Ce3+ luminescence shows broad bands due to moderate electron-phonon interaction in the 5d excited state. Three distin ct Ce3+ sites in the crystal were assigned from the optical spectra. The lu minescence spectrum from the dominant Ce3+ site has a large Stokes shift (s imilar to 8300 cm(-1)), whereas that from one of the two minor Ce3+ sites h as a Stokes shift of half that magnitude (similar to 4400 cm(-1)), assuming that the excitation spectrum is almost the same as for the dominant site. The peaks of the lowest-energy absorption and luminescence bands for the ot her minor Ce3+ site are shifted to lower energy, and the Stokes shift energ y (similar to 7800 cm(-1)) is close to that for the dominant site. These th ree Ce3+ sites are assigned to configurations of Ce3+ accompanied by differ ent charge compensators. This assignment is consistent with preliminary ele ctron spin-resonance results indicating that there exist two tetragonal and two orthorhombic Ce3+ centres in the absence of the cubic centre.