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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Electron Paramagnetic Resonance (EPR) studies on the photo-thermo ionization process of photo-thermo-refractive glasses

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Author(s):
Magon, Claudio Jose ; Donoso Gonzalez, Jose Pedro ; Lima, Jose Fernando ; Eckert, Hellmut ; Zanotto, Edgar D. ; Lumeau, Julien ; Glebova, Larissa ; Glebov, Leonid
Total Authors: 8
Document type: Journal article
Source: Journal of Non-Crystalline Solids; v. 452, p. 320-324, NOV 15 2016.
Web of Science Citations: 5
Abstract

Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive sodium alumino silicate glass, containing NaF and KBr additives, along with cerium, silver, tin and antimony oxide dopants. UV-exposed regions of this glass produce NaF nanocrystals upon heating, giving rise to a permanent localized refractive index change. In this article we examine the initial stages of this crystallization process by continuous-wave and pulsed X-band electron paramagnetic resonance (EPR) spectroscopy. UV exposure of PTR glass produces unpaired electrons whose EPR spectrum is characterized by pronounced peak splitting arising from nuclear magnetic hyperfine interactions with spin-5/2 and spin-7/2 nuclei suggesting close proximity of the unpaired electrons with Sb-121 and Sb-123 nuclei. These results indicate that the Sb2O3 dopant plays a key role in the initial stages of the crystallization mechanism. Upon thermal annealing, leading to the crystallization of NaF, these species disappear, indicating their transient nature. A number of other unpaired electron species identified in the dopant free matrix appear to be unrelated to the crystallization process. These results clearly challenge the classical mechanism proposed decades ago to explain the complex crystallization process of PTR glass. Together with more recent results from optical spectroscopy they support the Nikonorov model involving (1) photoionization of Ce3+, (2) transfer of this electron to Sb5+ species to create a Sb4+ species, (3) upon annealing electron transfer from Sb4+ to Ag+ ions, producing silver atoms, (4) coalescence of these species into Ag dusters, which (5) serve as nucleation catalysts for NaF nanocrystals. (C) 2016 Elsevier B.V. All rights reserved. (AU)

FAPESP's process: 13/07793-6 - CEPIV - Center for Teaching, Research and Innovation in Glass
Grantee:Edgar Dutra Zanotto
Support type: Research Grants - Research, Innovation and Dissemination Centers - RIDC