The x-ray storage phosphor properties of fluorozirconate glasses doped with Eu 2+ and Br - were interpreted previously to be due to BaBr 2 :Eu 2+ crystalline precipitates. In order to compare their behaviour with BaBr 2 :Eu 2+ single crystals, we grew such single crystals and investigated them with electron paramagnetic resonance (EPR). The Eu 2+ EPR spectra show local C S symmetry, with an isotropic g value 1.990 and an isotropic hyperfine constant 151 A = -31.0×10 -4 . The principal axes of the zero field splitting tensor in the mirror plane are rotated by an angle of 18° with respect to the crystallographic axes, as expected for the Ba 2+ 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 Eu 2+ shows that indeed crystalline BaBr 2 :Eu 2+ precipitates are present in such glass ceramics.
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Schweizer et al. (2001) studied this question.
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