Structural and spectroscopic study of oxyfluoride glasses and glass-ceramics using europium ion as a structural probe

Transparent oxyfluoride glasses and β-PbF2 nanocrystals containing glass-ceramics were prepared with varying Eu3+ content (0.3, 0.4, 0.5 and 0.6%). The effect of Eu3+ content on the preparation of glass-ceramics was investigated. From differential scanning calorimetry, the Tx-Tg (Tx-temperature of the onset of crystallization; Tg-glass transition temperature) parameter for glasses has shown slight variation, and an exothermic peak near Tg called the ceramization temperature (Tc) has been observed. Heat treatments were performed at this temperature to obtain transparent glass-ceramics containing β-PbF2 nanocrystals, identified by x-ray diffraction. Heat treatments for different periods of time were performed and were observed to be very important in the control of the crystal size and of the crystallization rate. Based upon the absorption spectra, the scattering level due to the presence of β-PbF2 nanocrystals in the glass-ceramics was observed to be similar to that for the mother glasses. Detailed analysis of emission spectra and decay time measurements led to the identification of Eu3+ ions as the β-PbF2 crystalline phase. Excitation spectra at 70 K show the interaction of Eu3+ ions with the fluorogermanate network