Generation mechanism of photoinduced paramagnetic centers from preexisting precursors in high-purity silicas

Nishikawa, Hiroyuki; Nakamura, Ryuta; Tohmon, Ryoichi; Ohki, Yoshimichi; Sakurai, Yuryo; Nagasawa, Kaya; Hama, Yoshimasa

doi:10.1103/physrevb.41.7828

Cited by 94 publications

(43 citation statements)

References 19 publications

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“…The "wet" OHC, which consists of a hole trapped on a single nonbridging oxygen, [71] is also called nonbridging oxygen hole center (NBOHC, SiOC). [72][73][74] The signal shape of the resonance near g = 2.04 is more in agreement with "dry" OHC ( SiOOC). Furthermore, the NBOHC signal ( SiOC) is usually associated with an optical absorption at 2 eV, although with a weak oscillator strength [75] , and we did not measure any significant coloration in the visible by diffuse reflectance spectroscopy.…”

Section: Epr Measurements Of Dried and Hydrated Glassessupporting

confidence: 58%

“…Furthermore, the NBOHC signal ( SiOC) is usually associated with an optical absorption at 2 eV, although with a weak oscillator strength [75] , and we did not measure any significant coloration in the visible by diffuse reflectance spectroscopy. Such defects have been proposed to arise from pre-existing defects in bulk silica [73,76] or from radiationless decays of excitons. [74,77,78] Moreover, we did not observe E' center ( SiC) type of defects.…”

Section: Epr Measurements Of Dried and Hydrated Glassesmentioning

confidence: 99%

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Radiolysis of Confined Water: Hydrogen Production at a High Dose Rate

Caër¹,

Rotureau²,

Brunet³

et al. 2005

ChemPhysChem

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The production of molecular hydrogen in the radiolysis of dried or hydrated nanoporous controlled-pore glasses (CPG) has been carefully studied using 10 MeV electron irradiation at high dose rate. In all cases, the H2 yield increases when the pore size decreases. Moreover, the yields measured in dried materials are two orders of magnitude smaller than those obtained in hydrated glasses. This proves that the part of the H2 coming from the surface of the material is negligible in the hydrated case. Thus, the measured yields correspond to those of nanoconfined water. Moreover, these yields are not modified by the presence of potassium bromide, which is a hydroxyl radical scavenger. This experimental observation shows that the back reaction between H2 and HO* does not take place in such confined environments. These porous materials have been characterized before and after irradiation by means of Fourier-transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) techniques, which helps to understand the elementary processes taking place in this type of environment, especially the protective effect of water on the surface in the case of hydrated glasses.

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Section: Epr Measurements Of Dried and Hydrated Glassessupporting

confidence: 58%

Section: Epr Measurements Of Dried and Hydrated Glassesmentioning

confidence: 99%

Radiolysis of Confined Water: Hydrogen Production at a High Dose Rate

Caër¹,

Rotureau²,

Brunet³

et al. 2005

ChemPhysChem

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show abstract

“…The generation of defects by UV photons occurs by bond cleavage at a site of the vitreous lattice via two main mechanisms [2][3][4]: (i) one-photon process giving rise to the transformation of native precursor centers whose radiolysis needs energy less than the energy gap (Eg $ 9 eV); (ii) multi-photon process able to promote valence to conduction band transitions originating holeelectron pairs whose dissociation at a site induces the bond cleavage.…”

Section: Introductionmentioning

confidence: 99%

Post UV irradiation annealing of E′ centers in silica controlled by H2 diffusion

Cannas

Costa

Boscaino

et al. 2004

Journal of Non-Crystalline Solids

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“…As a result, PL bands at about 3.02 eV, 2.73 eV, 2.37 eV,1.99 eV, and 1.55 eV, were identified, which are respectively related to: weak-oxygen bond (WOB) [44], Neutral Oxygen Vacancy (NOV) [45], E' δ center [46], non-bridging oxygen hole center (NBOHC) [18,47,48] and dangling bonds (DB) [49]. It was found that NBOHC and E' δ centers are the dominant radiative defects for each of the coated films.…”

Section: Photoluminescence Propertiesmentioning

confidence: 99%

Luminescent Properties of Silicon Nanocrystals:Spin on Glass Hybrid Materials

et al. 2017

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Abstract:The photoluminescence characteristics of films consisting of Si nanocrystals either coated with or embedded into Spin on Glass (SOG) were studied. Si nanocrystals showing red or blue luminescence when suspended in alcohol solution were obtained from porous silicon films. These were then either deposited in Si substrates and coated with SOG, or mixed in an SOG solution that was later spun on Si substrates. Both types of films were thermally annealed at 1100 • C for three hours in N 2 atmosphere. Transmission electron microscopy measurements showed a mean diameter of 2.5 nm for the Si nanocrystals, as well as the presence of polycrystalline Si nanoagglomerates. These results were confirmed by X-ray diffraction studies, which revealed the (111), (220) and (311) Bragg peaks in Si nanocrystals. Fourier transform infrared spectroscopy studies showed that the coated films present higher chemical reactivity, promoting the formation of non-stoichiometric SiO 2 , while the embedded films behave as a stoichiometric SiO 2 after the thermal annealing. The PL (photoluminescence) characterization showed that both embedded and coated films present emission dominated by the Quantum Confinement Effect before undergoing any thermal treatment. After annealing, the spectra were found to be modified only in the case of the coated films, due to the formation of defects in the nanocrystals/SiO 2 interface.

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Generation mechanism of photoinduced paramagnetic centers from preexisting precursors in high-purity silicas

Cited by 94 publications

References 19 publications

Radiolysis of Confined Water: Hydrogen Production at a High Dose Rate

Radiolysis of Confined Water: Hydrogen Production at a High Dose Rate

Post UV irradiation annealing of E′ centers in silica controlled by H2 diffusion

Luminescent Properties of Silicon Nanocrystals:Spin on Glass Hybrid Materials

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