Preparation and Characterization of High‐Purity Metal Fluorides for Photonic Applications

Abstract

We combine chelate‐assisted solvent extraction (CASE) and hot hydrogen fluoride gas treatment to enable a general method for the preparation of high‐purity binary metal fluorides. The fluorozirconate glass ZBLANI:Yb3+ (ZrF4–BaF2–LaF3–AlF3–NaF–InF3–YbF3), a solid‐state laser‐cooling material, is used as a test case to quantitatively assess the effectiveness of the purification method. The reduction of transition‐metal and oxygen‐based impurities is quantified directly by inductively coupled plasma mass spectrometry (ICP‐MS) and indirectly by laser‐induced cooling, respectively. The concentrations of Cu, Fe, Co, Ni, V, Cr, Mn, and Zn impurities in the ZrCl2O precursor solution were measured individually by ICP‐MS at various stages of the purification process. CASE was found to reduce the total transition‐metal concentration from 72500 to ~100 ppb. Laser cooling was most efficient in ZBLANI:Yb3+ glass fabricated from CASE‐purified metal fluoride precursors, confirming the results of the ICP‐MS analysis and demonstrating the effectiveness of the purification methods in a finished optical material. High‐purity metal fluorides prepared by the methods presented herein will enable new high‐performance optical materials for solid‐state optical refrigerators, crystals for vacuum ultraviolet (VUV) spectroscopy of the Thorium‐229 nucleus, VUV optics, fibers, and thin‐film coatings.