Preparation and analysis of Eu3+- and Eu2+-doped ZBLAN and ZBLALi fluorozirconate glasses

Fluorozirconate glasses in the ZBLAN and ZBLALi families with varying [Eu2+] and [Eu3+] concentrations were prepared and characterized. The reversible electroactivity of Eu2+/3+ was verified by cyclic voltammetry in the molten salt precursor phase, showing that Eu2+ would not reduce the other glass components. Eu2+-containing glasses were prepared by various strategies including inclusion of EuF2 as a starting material and chemical reduction during melt processing. Glass samples were characterized by differential scanning calorimetry, UV–Visible and IR spectroscopy and temperature-dependent conductivity. Glasses in the range of 0–6% [Eu3+] and ‘mixed valent’ ones with 0–3% [Eu2+] and 4–2% [Eu3+] were successfully prepared, but greater Eu concentrations spoiled the glass optical properties. The temperature-dependent bulk conductivities of numerous glasses were carefully measured using a Fourier analysis that resolves bulk and substantial interfacial contributions to glass conductivity. No systematic changes in glass conductivity were observed for glasses as a function of the [Eu2+][Eu3+] concentration product as would be expected were there a substantial rate of electron transfer between Eu sites, implying substantial and static structural differences between these sites.