Crystal field effects in REOBr:Eu3+

Crystal field parameters (Bkq) were obtained for the REOBr:Eu3+ series (RE = Y, La, Gd) and LaOI:Eu3+ from the analysis of fluorescence spectra. The sets of five nonzero Bkq parameters for the C4v symmetry reproduce the experimental 7FJ Stark level schemes within a few cm−1. The Racah (E0–3) and spin–orbit (ζ) parameters were determined for the REOBr:Eu3+ series with the aid of excitation spectra. Only insignificant shifts were observed in the parameter values along the series. A simulation of the Stark level sequences of excited levels was carried out on a strongly reduced basis set of 2S+LLJM levels. A poor simulation was obtained unless the free-ion wave functions were well defined. A comparison of the crystal field parameters for the whole REOX:Eu3+ series (RE = Y,La,Gd; X = Cl, Br,I) shows an increase in the strength of the crystal field with increasing ionic radius of the RE3+ host cation. A similar pattern prevails in the oxyhalide series from the oxychloride to the oxybromide host. The crystal field effect in LaOI:Eu3+ is practically equal to that in LaOBr:Eu3+.