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

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• 作者：Marcos de Oliveira Jr. ; Tássia S. Gonçalves ; Cynthia Ferrari ; Claudio José Magon ; Paulo S. Pizani ; Andrea S. S. de Camargo ; Hellmut Eckert
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 9, 2017
• 年：2017
• 卷：121
• 期：5
• 页码：2968-2986
• 全文大小：1018K
• ISSN：1932-7455

文摘

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.