Short- and Medium-Range Order in Photothermal Refractive Glass Revealed by Solid-State NMR Techniques

Abstract

Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive Na 2 O−ZnO−Al 2 O 3 − SiO 2 glass, containing NaF and KBr additives, along with cerium, silver, tin, and antimony oxide dopants. After heating above 500 °C, UV-exposed regions of this glass produce permanent refractive index changes, resulting from precipitation of NaF nanocrystals. Short-and medium-range order of this glass system is studied via multinuclear single-and double-resonance solid-state nuclear magnetic resonance (NMR) spectroscopy in regular PTR glass and in model glasses with simplified compositions. The results, when combined with data from energy-dispersive X-ray spectroscopy, indicate that the NaF component modifies the standard aluminosilicate framework, producing small amounts of F-bonded fiveand six-coordinated aluminum species. The fluoride speciation is obtained from 19 F magic-angle spinning NMR spectra, supported by 19 F{ 27 Al} and 19 F{ 23 Na} dipolar recoupling experiments. The majority of fluoride within the PTR glass is found within Na-dominated local environments, which also interact strongly with the aluminum. 23 Na{ 19 F} rotational echo double resonance reveals that about 1/3 of the Na + ions have fluoride ions in their first coordination spheres.

Transparent Aluminosilicate Oxyfluoride Glass Ceramics Containing Upconversion Luminescent CaF2 Nanocrystals: Glass-to-Crystal Structural Evolution Studied by the Advanced Solid-State NMR Spectroscopy

“…Part b summarizes the curves of the site-resolved relative attenuated amplitude ( S 0 – S )/ S versus mixing time ( NT r ). The ( S 0 – S )/ S 0 values are obtained by integrating the narrow regions covering the signals of Al­(IV), Al­(V), and Al­(VI), respectively . It is clear that the signals of Al­(V) and Al­(VI) show much stronger attenuation than that of Al­(IV), confirming that these species are in close proximity to F, while Al­(IV) species are remote from F. From these REDOR curves, experimental second moment values M 2 Al‑F are derived and summarized in Table .…”

Steady-State Free Precession and Solid-State NMR: How, When, and Why

“…Prof. Helmut Eckert’s career has demonstrated that solid-state NMR is one of the best methods available for extracting site-resolved chemical insight, about otherwise hopelessly complex, disordered, seemingly intractable materials. − These include many technologically relevant systems such as glasses, ceramics, ion conductors, catalysts, and bioactive materials. − Whereas solid-state NMR information is uniquely rich, the method faces well-known sensitivity limitations, which translate in turn into constraints on the kind of systems it can study. This weakness affects unreceptive low-γ or low-abundance nuclides, in general, and many half-integer quadrupolar nuclei in solids, in particular, where sensitivity may be further compromised by broad lines spreading signals even further into the noise. , Methods to boost the sensitivity of unreceptive nuclei have thus been the focus of intensive research. − One widely used approach in the resulting toolbox is the Carr-Purcell Meiboom-Gill (CPMG) sequence, , which, although originally introduced for T 2 measurements, was found useful to increase the sensitivity of solids NMR spectra affected by significant inhomogeneous broadenings. − The approach is commonly used for enhancing the sensitivity of quadrupolar nuclei NMR spectra, − particularly in static cases where T 2 * ≪ T 2 .…”

Fluorophosphate Upconversion-Luminescent Glass-Ceramics Containing Ba2LaF7:Er3+ Nanocrystals: An Advanced Solid-State Nuclear Magnetic Resonance Study

“…Upconversion-luminescent materials can achieve the conversion of infrared light into visible light. They exhibit promising applications in various fields such as solid-state lasers, information storage and processing, sensing and biological imaging, lighting sources, and three-dimensional (3D) displays. − Transparent fluorophosphate glass-ceramics containing fluoride nanocrystals are excellent upconversion-luminescent materials that possess the advantages of good chemical stability and mechanical properties of oxide glass, low phonon energy of fluoride crystal, and high solubility of rare-earth ions of phosphate glass. , Glass-ceramics can be prepared by heating a precursor glass at the desired temperature; they can be easily processed into optical fibers, large blocks, and so forth.…”

“…1−12 Transparent fluorophosphate glass-ceramics containing fluoride nanocrystals are excellent upconversionluminescent materials that possess the advantages of good chemical stability and mechanical properties of oxide glass, low phonon energy of fluoride crystal, and high solubility of rareearth ions of phosphate glass. 13,14 Glass-ceramics can be prepared by heating a precursor glass at the desired temperature; they can be easily processed into optical fibers, large blocks, and so forth.…”

“…13 They applied a 31 P/ 23 Na and 31 P/ 19 F double-resonance nuclear magnetic resonance (NMR) strategy to glasses in the system (BiF 3 ) y (50NaPO 3 −20Ba(PO 3 ) 2 −20NaF−10BaF 2 ) 100−y 12 and found that the successive reduction of the dipolar second moment M 2 (Na−P) with increasing BiF 3 content reflected increasing competition of fluoride ions for ligation with Na + ions. They also applied 19 F/ 23 Na double-resonance NMR in Na 2 O−ZnO−Al 2 O 3 −SiO 2 −KBr glasses 14 and revealed that about 1/3 of the Na + ions have fluoride ions in their first coordination spheres. Moreover, in NaPO 3 −AlF 3 glasses, 34 19 F/ 23 Na and 19 F/ 27 Al double-resonance NMR experiments indicate that the Al-bound terminal F atoms interact significantly more strongly with sodium ions than the Pbonded terminal F atoms, which is consistent with local charge considerations.…”