Structure–Property Relations in Fluorophosphate Glasses: An Integrated Spectroscopic Strategy

Abstract

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.

Structural elucidation of NASICON (Na3Al2P3O12) based glass electrolyte materials: effective influence of boron and gallium

“…The B and Ga cations were substituted to observe the changes in the structure of the NCAP glass and thereby to utilise them for further improvement in the conductivity of NCAP glass. The 27 Al, 11 B, 71 Ga, 23 Na, and 31 P MAS-NMR and microRaman techniques were utilised to elucidate the structure of the newly designed glasses. The modied glass materials were also characterised, using impedance measurements, to check their applicability as an electrolyte material for batteries.…”

“…23 Among the various techniques, magic angle spinning-nuclear magnetic resonance (MAS-NMR) and micro-Raman confocal spectroscopies are reliable techniques for structural characterization of glass materials. Solid-state NMR is particularly applicable for probing the coordination numbers of spin active nuclei such as 23 Na, 31 P and 27 Al, network connectivity and, in favourable cases, next-nearest neighbour (NNN) connectivity, whilst Raman and infrared spectroscopy can be utilised to probe the nature of the bond between the metal cation and its surrounding oxygen anion.…”

“…The present study demonstrates the changes in the Na + ion conductivity of NCAP bulk glass with the substitution of boron (NCABP: Na 2. 27 Al, 23 Na, 11 B and 71 Ga nuclei) were used. The Raman spectrum revealed that the NCAP glass structure is more analogous to the AlPO 4 mesoporous glass structure.…”

“…The 31 P MAS-NMR spectrum illustrated that the NCAP glass structure consists of a high concentration of Q 0 (3Al) units, followed by Q 0 (2Al) units. The 27 Al MAS-NMR spectrum indicates that alumina exists at five different sites, which include AlO 4 units surrounded by AlO 6 units, Al(OP) 4 , Al(OP) 5 , Al(OAl) 6 and Al(OP) 6 , in the NCAP glass structure. The Ga MAS-NMR spectrum suggests that gallium cations in the NCAGP glass compete with the alumina cations and occupy four (GaO 4 ), five (GaO 5 ) and six (GaO 6 ) coordinated sites.…”

“…Fig. 3 shows the 27 Al MAS-NMR spectra for all the glasses. Each spectrum shows three resonance peaks including the peak at the higher chemical shi side that can be assigned to the AlO 4 units.…”