Structural phase changes in barium bromide nano-crystals in a fluorobromozirconate glass-ceramic x-ray storage phosphor

The structural changes in a fluorobromozirconate glass ceramic containing a ratio of 5% bromine to fluorine ions, following thermal annealing in the range 240-300 degreesC, are reported. The changes were monitored through xray diffraction, and the photoluminescence (PL) and electron paramagnetic resonance of EU2+ dopant ions. In the range of 240-275 degreesC, the barium and bromine ions in the glass precipitate to form the metastable hexagonal phase of barium bromide. The Eu2+ PL spectrum comprises a narrow band at 410 mn, and a weaker broad band centred at 485 nm. The 410 nm band is assigned to two unresolved 4f(6) 5d(1) --> 4f(7) emissions from Eu2+ ions at the two Ba2+ sites in this phase, whilst the 485 nm band is assigned to an impurity associated site or cluster. On annealing at 290 degreesC, the hexagonal phase transforms to the stable orthorhombic phase, and the PL spectrum comprises a single narrow band centred at 404 run, assigned to a 4f(6) 5d(1 -->) 4f(7) emission from Eu2+ ions at the single Ba2+ site in the orthorhombic phase.