Polarized laser selective excitation studies were made of material that was doped with Er3+. It was concluded that it had a C3v symmetry which was of a similar nature to the trigonally symmetrical J-center that had been reported for SrF2 crystals doped with Er3+. Deviations from the expected polarization ratios for exact C3v symmetry indicated the presence of static low-symmetry distortions of the rare-earth ion environment. This was confirmed by Zeeman infra-red absorption measurements. A crystal-field analysis, which assumed an exact C3v symmetry for both the BaF2:Er3+ and SrF2:Er3+ centers furnished good predictions of the experimental energy levels and magnetic splitting factors.

Site Selective Spectroscopy of the C3v Symmetry Center in Er3+ Doped BaF2. J.P.R.Wells, T.Dean, R.J.Reeves: Journal of Luminescence, 2002, 96[2-4], 239-48