Network Structure and Rare-Earth Ion Local Environments in Fluoride Phosphate Photonic Glasses Studied by Solid-State NMR and Electron Paramagnetic Resonance Spectroscopies

A detailed structural investigation of a series of fluoride phosphate laser glasses with nominal composition 25BaF2–25SrF2–(30 – x)Al(PO3)3–xAlF3–(20 – z)YF3:zREF3 with x = 25, 20, 15 and 10, RE = Yb and Eu, and 0 ≤ z ≤ 1.0 has been conducted using Raman, solid-state nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) spectroscopies. The network structure is dominated by the preferred formation of aluminum-to-phosphorus linkages, which have been quantified by means of 27Al/31P NMR double-resonance techniques. The fluoride ions are found in mixed Al/Y/Ba/Sr environments accommodating the luminescent dopant species as well. The local environments of the rare-earth species have been studied by pulsed EPR spectroscopy of the Yb3+ spin probe (S = 1/2), revealing composition-dependent echo-detected lineshapes and strong hyperfine coupling with 19F nuclei in hyperfine sublevel correlation (HYSCORE) spectra consistent with the formation of Yb3+–F bonds. In addition, photoluminescence spect...