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

Abstract

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.

Spying with spins on messy materials: 60 Years of glass structure elucidation byNMRspectroscopy

“…The above pulsed EPR methods present a new approach to rare‐earth‐doped luminescent glasses . Figure shows results for a series of 25BaF 2 –25SrF 2 –(30− x )Al(PO 3 ) 3 – x AlF 3 −19.75YF 3 −0.25YbF 3 glasses.…”

“…[79][80][81][82][83][84][85][86] The above pulsed EPR methods present a new approach to rare-earth-doped luminescent glasses. 73,87,88 Figure 15 shows results for a series of 25BaF 2 -25SrF 2 -(30Àx)Al (PO 3 ) 3 -xAlF 3 À19.75YF 3 À0.25YbF 3 glasses. Here, the electron spins associated with the paramagnetic Yb 3+ ions serve as the spies of their electronic and nuclear environments.…”

“Gene” modeling approach to new glass design

“…The C‐S‐P methodology offers: Identification of a set of influential genes that have specific roles in controlling a variety of glass properties; Transformation of one dimension compositional effect to multidimension structural effects on the very same set of glass properties, which especially attractive to address problems that arise from single‐component studies, in which nonlinear glass property responses occur; Building potentially better models by introducing interactions of specific pairs of genes (for example, the published NMR results indicated the dominance of P‐O‐Al rather than P‐O‐RE (RE = rare earth) in fluorophosphate glass system under investigation, the finding enables a structural‐based justification in the S‐P model to include a cross/interaction term between P 2 O 5 and Al 2 O 3 . (cf.…”

“…Measured (black symbol) and simulated (red line) spectra of the BL glass and individual bands (blue lines and dotted line) with plausible band assignments according to literature and difference between the simulated and measured spectrum (δ—bending mode, υ s —symmetric stretching mode, υ as —asymmetric stretching mode, Q n —number of bridging oxygen per PO 4 unit, P = O double oxygen bond or terminal oxygen).…”

“…Focusing on the glass‐network‐related structural bands, Figure shows the measured and simulated IR spectrum of the BL glass along with individual bands derived from the curve‐fitting over the frequency range from 400 cm −1 and 1650 cm −1 ; plausible network structural units are assigned according to literature . The difference between the simulated and measured has a random distribution and generally significantly smaller than ± 0.5 abs/cm unit.…”