Conformational disorder in vitreous systems probed by photoluminescence activity inSiO2

Abstract

The emission bands ␣ E ͑4.2 eV͒ and ␤ ͑3.1 eV͒ have been investigated in a variety of as-grown natural silica types. We report experimental results on the stationary photoluminescence spectra and their relationship with the absorption band B 2␤ ͑5.15 eV͒, on the temperature dependence of their competition, on their excitation pathway and their kinetic decay ensuing a pulse excitation. We use our results to characterize the electronic transitions involved and the intersystem crossing process linking the two excited states. Our results evidence the role played by the conformational disorder. In particular, we make use of a model in which the interconversion processes between conformational substates are effective at high temperature (TϾ200 K) and become frozen at low temperature (TϽ120 K). Finally we discuss our results on the basis of a structural model ascribing these optical activities to an oxygen deficient center related to a Ge impurity.

Bleaching of optical activity induced by UV laser exposure in natural silica

“…This is in contrast with recent works on X-irradiated Ge-doped silica [8] and UV irradiated Ge-doped optical fiber preforms [9], both showing a lack of correlation among these optical bands. We point out that the linear correlation between OA and PL bands involves a constant luminescence quantum yield, while that between the two emissions is based on a constant intersystem crossing rate linking the excited singlet and triplet states from which 4.28 eV and 3.14 eV emissions take place, respectively [17][18][19]. Hence, a departure from correlation can arise from a variation of these parameters induced by a selective conversion of centers whose features are inhomogeneously distributed [19][20][21].…”

“…We point out that the linear correlation between OA and PL bands involves a constant luminescence quantum yield, while that between the two emissions is based on a constant intersystem crossing rate linking the excited singlet and triplet states from which 4.28 eV and 3.14 eV emissions take place, respectively [17][18][19]. Hence, a departure from correlation can arise from a variation of these parameters induced by a selective conversion of centers whose features are inhomogeneously distributed [19][20][21]. This is consistent with the observed change of the ratio between the emission intensities at 3.14 eV and 4.28 eV evidenced in our results.…”

Deciphering metal-induced oxidative damages on glycated albumin structure and function

“…For each fluorescence spectrum, the zeroth (M 0 ) and the first (M 1 ) moments of the spectral distribution A (E) were calculated from the experimental data, after subtracting the tangent to the minima of each band, according to the following formula [39]:…”

Synthesis and characterization of CdS nanoparticles embedded in a polymethylmethacrylate matrix

“…5, respectively), we note a significant dependence on excitation wavelength, as evidenced by the inversion of the intensity ratio of the two emissions. As reported in the literature for other systems, this suggests the presence of a conformational distribution of particles having slightly different spectral properties that can be selectively excited at different wavelengths [26][27][28].…”