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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The structure of laser glasses in the system (B 2 O 3 ) 0.6 {(Al 2 O 3 ) 0.4-x (Y 2 O 3 ) x } (0.1 e x e 0.25) has been investigated by means of 11 B, 27 Al, and 89 Y solid state NMR as well as Y-3d core-level X-ray photoelectron spectroscopy. 11B magic-angle spinning (MAS) NMR spectra reveal that the majority of the boron atoms are three-coordinated, and a slight increase of four-coordinated boron content with increasing x can be noticed. 27 Al MAS NMR spectra show that the alumina species are present in the coordination states four, five and six. All of them are in intimate contact with both the three-and the four-coordinate boron species and vice versa, as indicated by 11 B/ 27 Al rotational echo double resonance (REDOR) data. These results are consistent with the formation of a homogeneous, nonsegregated glass structure. For the first time, 89 Y solid state NMR has been used to probe the local environment of Y 3+ ions in a glass-forming system. The intrinsic sensitivity problem associated with 89 Y NMR has been overcome by combining the benefits of paramagnetic doping with those of signal accumulation via Carr-Purcell spin echo trains. Both the 89 Y chemical shifts and the Y-3d core level binding energies are found to be rather sensitive to the yttrium bonding state and reveal that the bonding properties of the yttrium atoms in these glasses are similar to those found in the model compounds YBO 3 and YAl 3 (BO 3 ) 4 . Based on charge balance considerations as well as 11 B NMR line shape analyses, the dominant borate species are concluded to be meta-and pyroborate anions.