11 February 2008 Synthesis of ultrapure ZBLAN glass for laser refrigeration
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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 ~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.
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Markus P. Hehlen, Markus P. Hehlen, Richard I Epstein, Richard I Epstein, Wendy M. Patterson, Wendy M. Patterson, "Synthesis of ultrapure ZBLAN glass for laser refrigeration", Proc. SPIE 6907, Laser Refrigeration of Solids, 69070A (11 February 2008); doi: 10.1117/12.762146; https://doi.org/10.1117/12.762146

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