25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

Photo-thermo refractive Glasses: NMR and EPR Mechanistic Studies

Not scheduled
4h
Harnack House and Henry Ford Building

Harnack House and Henry Ford Building

Board: 135
Poster Posters

Speaker

Ms Lena Marie Funke (University of Münster, Institute of Physical Chemistry)

Description

Photo-thermo refractive (PTR) glasses are photosensitive glasses of composition 70SiO$_2$•15Na$_2$O•5NaF•5ZnO•4Al$_2$O$_3$•1KBr that are doped with small quantities of CeO$_2$, Ag$_2$O, Sb$_2$O$_3$, and SnO$_2$ (0.01 mol %). Their refractive index can be modified with high spatial resolution using focused UV irradiation and subsequent annealing close to the glass transition temperature. This enables manufacturing of various important optical components and devices (e.g. Bragg gratings, holograms and components to control the length of laser pulses).$^1$ However, the structure of the glass, the origin of the refractive index change, and the role of Sb$_2$O$_3$, SnO$_2$ and KBr are not yet fully understood.
Here, the short- and medium-range order of the glass system is studied for the first time by multinuclear single- and double-resonance solid-state nuclear magnetic resonance (NMR) spectroscopy.$^2$ $^{23}$Na{$^{19}$F} REDOR experiments are useful for measuring the fraction of F-bonded Na$^+$ ions, giving insights into their spatial distribution.
By means of CW and pulsed EPR spectroscopy, the paramagnetic species, formed by UV irradiation, are identified.$^3$ The vicinity of photosensitive and photoactivated centers (Ce$^{3+}$ and ”Sb$^{4+}$”) is further studied by Electron Spin Echo Envelope Modulation (ESEEM) and HYperfine Sub-level Correlation (HYSCORE) Spectroscopies. Based on the electron’s hyperfine interactions with nearby nuclear spins, we obtain new insights on the role of the dopants in the initial steps of photoexcitation. Finally, combining $^{19}$F MAS NMR and CW EPR spectroscopy the formation of silver clusters (nucleation upon thermal annealing) can be monitored.

The authors are grateful for the support by FAPESP grant 2013/07793-6 and thank Professor Leonid Glebov (University of Central Florida) for providing the samples. LMF thanks the Stiftung der Deutschen Wirtschaft for a doctoral stipend.

(1) L. Glebov, Proc. SPIE 2007, 6545, 654507.
(2) L. M. Funke et al., Phys. Chem. C 2019, 123, 12411.
(3) C. J. Magon et al., J. Non.-Cryst. Solids 2016, 452, 320.

Primary authors

Ms Lena Marie Funke (University of Münster, Institute of Physical Chemistry) Prof. Hellmut Eckert (University of Münster, Institute of Physical Chemistry; University of São Paulo, Institute of Physics) Prof. Michael Ryan Hansen (University of Münster, Institute of Physical Chemistry)

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