Photoluminescence and crystallization in europium-doped fluorobromozirconate glass-ceramics

We have investigated barium bromide crystallization in glasses which have an overall composition of 53% ZrF4, 20% BaF2, 5% NaF, 15% NaBr, 1% LaF3, 3% AlF3, 2% YF3, and 1% EuF2. The glasses were prepared by melting at 850°C in an inert atmosphere and quenching into a brass mold. Subsequent thermal treatment of the glass yields a transparent or translucent fluorozirconate glass containing BaBr2 crystals; this glass-ceramic material has potential applications as an X-ray storage phosphor. The glasses and glass-ceramics were investigated using photoluminescence, optical density, X-ray diffraction, and differential scanning calorimetry methods. Glasses which have been quenched to temperatures below 260°C are transparent and show no photoluminescence from the europium ions. When the glasses are subsequently heated above about 263°C, crystals of BaBr2 in the hexagonal phase start to precipitate and photoluminescence from Eu2+ ions is observed. It is possible to prepare the resulting glass-ceramic in transparent form by heating to temperatures just below the temperature of most rapid crystallization, Tx=280 C. The photoluminescence is attributed to Eu2+ ions replacing Ba2+ ions in the BaBr2 crystals.