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 r ange 240-300 degreesC, are reported. The changes were monitored through xra y diffraction, and the photoluminescence (PL) and electron paramagnetic res onance of EU2+ dopant ions. In the range of 240-275 degreesC, the barium an d bromine ions in the glass precipitate to form the metastable hexagonal ph ase 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 impurit y associated site or cluster. On annealing at 290 degreesC, the hexagonal p hase transforms to the stable orthorhombic phase, and the PL spectrum compr ises 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.