Abstract and subjects
The fluorozirconate glass ZBLAN:1%Yb3+ was synthesized, for the first time, from fluoride precursors that were individually purified by solvent extraction and hydrofluoric (HF) gas treatment. The synthesis used aqueous solutions of high-purity commercial precursors that were subjected to ultra-filtration followed by solvent extraction using ammonium pyrrolidine dithiocarbamate (APDC) and methyl-isobutyl-ketone (MIBK). The purified metal fluorides were precipitated and treated in hot HF gas to remove water, hydroxyl (OH-), and oxide impurities. ZBLAN: 1%Yb3+ was fabricated from these precursors by melting under inert atmosphere, yielding glasses with excellent mechanical properties and having a clear, bubble-free, and crystallite-free matrix. The effect of adding 0.5 mol% of In3+ as an oxidizer to suppress the reduction of Zr4+ and the accompanying formation of black precipitates was studied. We found evidence for an oxidizer concentration threshold of similar to 0.8 mol%. Glasses made from purified fluorides formed black precipitates even with the addition of 0.5 mol% In3+, while glasses made from commercial fluorides did not. In the latter, additional oxidizers were likely present in the form of transition-metal impurities. An In3+ oxidizer concentration of >0.8 mol% is expected to eliminate the black precipitates in purified glasses and to yield ZBLAN:Yb3+ glass for efficient laser cooling.