Optical spectroscopy of Ce3+ in BaLiF3

The optical absorption spectrum of Ce3+ in BaLiF3 crystals consists of several overlapping broad bands. The Ce3+ luminescence shows broad bands due to moderate electron-phonon interaction in the 5d excited state. Three distinct Ce3+ sites in the crystal were assigned from the optical spectra. The luminescence spectrum from the dominant Ce3+ site has a large Stokes shift (~8300 cm-1 ), whereas that from one of the two minor Ce3+ sites has a Stokes shift of half that magnitude (~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 other minor Ce3+ site are shifted to lower energy, and the Stokes shift energy (~7800 cm-1 ) is close to that for the dominant site. These three Ce3+ sites are assigned to configurations of Ce3+ accompanied by different charge compensators. This assignment is consistent with preliminary electron spin-resonance results indicating that there exist two tetragonal and two orthorhombic Ce3+ centres in the absence of the cubic centre.