EPR of Gd³⁺and Eu²⁺in fluorozirconate glasses

EPR spectra at 9.1 and 30 GHz are reported for the iso-electronic ions Gd 3+ and Eu 2+ in glasses of composition 0.50 ZrF 4 , 0.20 BaF 2 , 0.055 AlF 3 , 0.045 LaF 3 and 0.10 NaF or LiF. The spectra are similar to the 'U' spectra familiar in many oxide glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. For europium the mean crystal-field parameter, b 2 0 approximately=0.075 cm -1 , is 30% larger than that for gadolinium, b 2 0 approximately=0.058 cm -1 , suggesting that the two ions occupy significantly different sites. Whereas the trivalent gadolinium will substitute readily into La 3+ sites, it is likely that divalent europium ions replace Ba 2+ in sites where they are more weakly bound and have a higher fluorine coordination.