Search results for "Paramagnetic"
showing 10 items of 600 documents
Spectroscopy of an optical excited Ga doped SiO2 surface
2007
Abstract We present the first spectroscopical analysis of the Ga/SiO2 surface interaction in hot environment. This interaction gives rise to inclusions of Ga atoms inside the silica matrix that produce structural changes and modify the SiO2 optical characteristics. This paper discusses both the time- and the frequency-resolved spectra of the fluorescence emission following UV pulsed laser excitation of the so “doped” silica in the range 15,000–28,000 cm−1. The investigation is completed by the electron paramagnetic resonance (EPR) spectra of two high-purity synthetic silica samples of commercial origin after thermal treatment in presence and in absence of a Ga atmosphere.
Neutron-induced defects in optical fibers
2014
We present a study on 0.8 MeV neutron-induced defects up to fluences of 1017 n/cm2 in fluorine doped optical fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E', H(I), POR and NBOH Centers.
centers induced by γ irradiation in sol–gel synthesized oxygen deficient amorphous silicon dioxide
2007
The effects of room temperature γ-ray irradiation up to a dose of ∼1300 kGy are investigated by Electron paramagnetic resonance (EPR) measurements in amorphous silicon dioxide (a-SiO2) produced by a sol-gel synthesis method that introduces O{triple bond, long}Si{single bond}Si{triple bond, long}O oxygen deficiency. We have found that exposure to radiation generates the Eγ′ center with the same spectral features found in high purity commercial a-SiO2. The maximum concentration of defects induced in this sol-gel material indicates that its resistance to radiation is comparable to that of synthetic fused a-SiO2. The concentration of Eγ′ center increases with irradiation, featuring a sublinear …
Structure sensitive investigations on luminescence centres in Mn-activated LiBaF3 dosimeters
2008
Abstract Prior to x-irradiation the photoluminescence (PL) of Mn-activated LiBaF3 shows a Mn 2 + emission band at 710 nm; the corresponding excitation bands are between 210 and 620 nm. After x-irradiation the PL emission spectrum shows a band peaking at about 610 nm which is tentatively assigned to a perturbed Mn 2 + emission; the intensity of all PL emission bands is increased. Structure sensitive investigations on the radiation-induced emission band were done by detecting electron paramagnetic resonance (EPR) induced changes in the integral PL emission at a temperature of 1.5 K. The analysis of the angular dependent PL-EPR spectra, recorded for different orientations of the magnetic field…
RbBr and CsBr doped with Eu2+ as new competitive X-ray storage phosphors
2001
Abstract After X-irradiation of the alkali halides RbBr and CsBr doped with divalent Eu a significant photostimulated luminescence (PSL) effect was found. In both systems the electron trap centre is an F centre, the hole trap centre is still unknown. The Eu 2+ aggregation with cation vacancies plays an important role. Although all of the different Eu 2+ aggregates seem to show PSL effects, they have different PSL efficiencies, decay times and spectral characteristics. In the case of RbBr:Eu 2+ it was possible to investigate the different Eu 2+ -cation vacancy aggregate states by magnetic circular dichroism of the optical absorption (MCDA) and MCDA-detected electron paramagnetic resonance. I…
Optical and magnetic resonance spectroscopy of stimulated recombination processes in defect studies
2004
Optical and magnetic resonance spectroscopy is widely used in the investigation of radiation-induced processes in wide-gap solids. This paper discusses the present understanding of applications of the experimental methods of optical and thermoactivation spectroscopy in the research of new materials, for applications in radiation dosimetry and digital imaging and in the basic research into the fundamental physics and chemistry of radiation. The advantages of the simultaneous use of optical and magnetic resonance techniques for the investigation of stimulated processes are considered.
Activity of laccase on unbleached and bleached thermomechanical pulp
2003
The introduction of value-added properties to pulp fibres is an attractive proposition. One interesting option is targeted modification of fibre surfaces by enzymatic activation. In this work, the activity of laccase on pulp and pulp fractions from thermomechanical pulp (TMP) and peroxide bleached TMP was studied on the basis of consumption of the co-substrate oxygen in the reaction and by studying the formation of radicals in the pulp material as analysed by electron paramagnetic resonance spectroscopy (EPR). Laccases obtained from Trametes hirsuta and Myceliophthora thermophila were used in the study. Laccases were found to be active on pulp material of unbleached TMP, whereas only fines …
Rotation of methyl radicals in molecular solids.
2010
Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH(3)) in solid carbon monoxide, carbon dioxide, and nitrogen matrices. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm ArF excimer laser radiation during the gas condensation on the substrate. The ESR spectra exhibit anisotropic features that persist over the temperature range examined, and in most cases this indicates a restriction of rotation about the C(2) symmetry axis. A nonrotating CH(3) was also observed in a CO(2) matrix. The intensity ratio between the symmetric (A) and antisymmetric (E) nuclear spin states was recorded as a functi…
Unexpected Reaction of the Unsaturated Cluster Host and Catalyst [Pd3(3-CO)(dppm)3]2+ with the Hydroxide Ion: Spectroscopic and Kinetic Evidence of a…
2006
The title cluster, [Pd(3)(mu(3)-CO)(dppm)(3)](2+) (dppm=bis(diphenylphosphino)methane), reacts with one equivalent of hydroxide anions (OH(-)), from tetrabutylammonium hydroxide (Bu(4)NOH), to give the paramagnetic [Pd(3)(mu(3)-CO)(dppm)(3)](+) species. Reaction with another equivalent of OH(-) leads to the zero-valent compound [Pd(3)(mu(3)-CO)(dppm)(3)](0). From electron paramagnetic resonance analysis of the reaction medium using the spin-trap agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the 2-tetrahydrofuryl or methyl radicals, deriving from the tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) solvent, respectively, were detected. For both [Pd(3)(mu(3)-CO)(dppm)(3)](2+) and [Pd(3)(mu…
EPR, ENDOR and TRIPLE resonance of amino-substituted 9,10-anthraquinone radicals and the rotation of the amino groups in the solution phase
1996
EPR, ENDOR and TRIPLE resonance spectra were recorded for 1-amino-9,10-anthraquinone (1-aminoAQ), 2-aminoAQ, 1,2-diaminoAQ, 1.4-diaminoAQ, 1,5-diaminoAQ and 2,6-diaminoAQ anion radicals in the solution phase. The rotation of the amino groups is discussed with reference to the experimental data. Rotation barrier calculations were carried out using B3PW91/3-21G* density functional method. The amino groups at positions 1, 4, 5, 8 were found not to be in rotational movement up to the EPR time-scale.