A detailed structural investigation of a series of fluoride phosphate laser glasses with nominal composition 25BaF 2 -25SrF 2 -(30-x)Al(PO 3 ) 3 -xAlF 3 -(20-z)YF 3 :zREF 3 with x = 25, 20, 15 and 10, RE = Yb and Eu and 0 ≤ z ≤ 1.0 has been conducted, using Raman, solidstate 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 27 Al/ 31 P 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 Yb 3+ spin probe (S = ½), revealing composition dependent echo-detected lineshapes, and strong hyperfine coupling with 19 F nuclei in hyperfine sublevel correlation (HYSCORE) spectra consistent with the formation of Yb 3+ -F bonds. In addition, photoluminescence spectra of Eu 3+ -doped samples reveal that the 7 F 2 -> 5 D 0 / 7 F 1 -> 5 D 0 transition intensity ratio, the normalized phonon sideband intensities in the excitation spectra as well as excited state lifetimes are systematically dependent on fluoride content.Altogether, these results indicate that the rare-earth ions are found in a mixed fluoride/phosphate environment, to which the fluoride ions make the dominant contribution. Nevertheless, even at the highest fluoride levels (x = 25) the data suggest residual rare-earth-phosphate coordination.

A detailed structural investigation of a series of fluoride phosphate glasses with nominal compositions 25BaF2-25SrF2–(30–x)­Al­(PO3)3–xAlF3–(20–z)­ScF3:zREF3 with x = 25, 20, and 15, RE = Yb and Eu, and 0 ≤ z ≤ 1.0, and of a Sc-free set of glasses with compositions w[80­(Ba/Sr)­F2–20AlF3]–(1–w)­[80Ba­(PO3)2–20Al­(PO3)3] (w = 25, 50, 75), doped with 0.2 mol % Yb3+ or Eu3+, has been conducted. As indicated by Raman scattering and solid state NMR, the network structure is dominated by aluminum–oxygen-phosphorus linkages, which can be quantified by means of 27Al/31P NMR double resonance techniques. The ligand environment of the rare-earth ions is studied by (1) 45Sc NMR of the diamagnetic mimic Sc3+, (2) pulsed X-band EPR spectroscopy of Yb3+ spin probes, and (3) excitation and emission spectroscopy of Eu3+ dopants. The rare-earth ions are found in a mixed environment of fluoride and phosphate ions, which changes systematically as a function of glass composition. In the Sc-containing glasses the quantitative makeup of this ligand environment has been determined by 45Sc­{19F} and 45Sc­{31P} rotational echo double resonance (REDOR). Comparison of the P- to F-ligand ratio with the batch composition indicates that the Sc3+ ions show a clear preference for phosphate over fluoride ion ligation. These REDOR results were correlated with Yb3+ EPR data, the intensity ratio of Eu3+ transitions 5D0 → 7F2 to 5D0 → 7F1, and the lifetime values of the Eu3+ emitting level 5D0. As a result, it was possible to obtain a global interpretation in terms of the associated quantitative ligand distribution (fluoride versus phosphate) in the first coordination sphere of the rare earth ions. The calibration of EPR and luminescence spectra on the basis of such solid state NMR data defines a new spectroscopic strategy for characterizing the rare-earth local environments in promising laser glasses.

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