EPR of Eu2+ in BaBr2 crystals and fluorobromozirconate glass ceramics

The x-ray storage phosphor properties of fluorozirconate glasses doped with Eu2+ and Br- were interpreted previously to be due to BaBr2:Eu2+ crystalline precipitates. In order to compare their behaviour with BaBr2:Eu2+ single crystals, we grew such single crystals and investigated them with electron paramagnetic resonance (EPR), The Eu2+ EPR spectra show local Ca symmetry, with an isotropic g value 1.990 and an isotropic hyperfine constant (152)A = -31.0 x 10(-4). The principal axes of the zero field splitting tensor in the mirror plane are rotated by an angle of 18 degrees with respect to the crystallographic axes, as expected for the Ba2+ site. A powder EPR spectrum was also recorded and successfully simulated using the single-crystal EPR data. Its close similarity with the EPR spectra in fluorobromozirconate glass ceramics doped with EU2+ shows that indeed crystalline BaBr2:Eu2+ precipitates are present in such glass ceramics.