Search results for "Absorption band"
showing 10 items of 143 documents
Optical absorption and Raman studies of neutron-irradiated Gd3Ga5O12 single crystals
2018
Abstract In this work we have performed a comparative analysis of optical absorption and micro-Raman spectra for series of Gd3Ga5O12 (GGG) single crystals irradiated by fast neutrons with fluences from 1016 n/cm2 to 1018 n/cm2. It was found that the optical absorption spectra of non-irradiated Czochralski grown GGG consist of the relatively narrow lines in the UV spectral range related to the 4f–4f transitions in Gd3+. Transitions from the 6S7/2 ground state to the 6P, 6J and 6D states in a Gd3+ cation are clearly detected. For a GGG crystal containing Ca impurity ions, additional absorption band at 350 nm is observed, and it is tentatively ascribed to oxygen vacancies associated with Ca im…
ESR and PL centers induced by gamma rays in silica
1996
We have studied the point defects created by γ irradiation in various types of commercial silica glasses, including both natural and synthetic samples, with different OH content, in the low dose regime (0.05–100 Mrad). We found that the growth rate of E′ centers depends strongly on the silica type, ranging from 2 × 1015 cm−3 Mrad−1 to 6 × 1017 cm−3 Mrad−1. Samples of natural silica are rather susceptible to γ ray exposure, as E′ concentration saturates (typically 5 × 1017 cm−3) for doses as low as a few Mrads. For both synthetic and natural samples, the radiation hardness is higher in wet than in dry silica. Moreover, we found a strict correlation between the concentration of E′ centers and…
The nature of the 4.8 eV optical absorption band induced by vacuum-ultraviolet irradiation of glassy SiO2
2000
Abstract The controversial optical absorption band centered at 4.8 eV, which is present in nearly all irradiated silicas, was investigated. It is caused by at least two different defects: non-bridging oxygen hole center (NBOHC) and interstitial ozone (O3). Both species have absorption bands at 4.8 eV, the O3-related band is identified by its susceptibility to bleaching by 4 to 5 eV photons, by a smaller halfwidth and by its independence from the NBOHC-associated 1.9 eV photoluminescence (PL) band. The contribution of NBOHC to the 4.8 eV band is dominant in most cases, while O3 is important in F2 excimer laser-irradiated samples of oxygen-rich glassy SiO2.
The behavior of interstitial oxygen atoms induced by F2 laser irradiation of oxygen-rich glassy SiO2
2002
Abstract Interstitial oxygen atoms in glassy silicon dioxide were created by photolysis of pre-existing interstitial oxygen molecules O 2 with a fluorine excimer laser (7.9 eV). The concentration of atomic oxygen interstitials was indirectly monitored by the disappearance and subsequent recovery of interstitial molecules which were monitored by their 1272 nm photoluminescence band. Most of the oxygen interstitials (>95%) are immobile at room temperature. The onset of their mobility occurs between 200 and 400 °C where around 95% of them recombine to form O 2 molecules. The high stability of interstitial oxygen atoms is consistent with the theoretical prediction that they are incorporated int…
Relaxation of electronic excitations in strontium titanate
2002
The transient absorption spectra and kinetics were studied for undoped, lead doped and high purity SrTiO 3 single crystals. The pulsed electron beam induced transient absorption is studied in all crystals. The strong absorption at 0.8 v eV was observed only in high purity SrTiO 3 . This absorption is suggested to arise from intrinsic electron polaron. The bound electron polarons are likely responsible for absorption band at 1.4 v eV. The main luminescence band under excitation pulse is observed at 2.75 v eV. The luminescence decay is faster than that of transient absorption.
The experimental observation of the potential barrier for self-trapped exciton decay into F-H pair in KCl-Na crystals
1995
Abstract The optical absorption induced by the electron pulse irradiation of Na+ doped KCl has been measured. Transient optical absorption band of FA centers was observed at 80 K (LNT). The temperature dependence of FA center formation was studied. It is proposed that the obtained activation energy originates from the potential barrier between the STE perturbed by the cation impurity and the nearest neighbour FA-H pair. The mechanism of the suppression of the defect formation by the monovalent cation impurity in alkali halide crystals is discussed.
UV and vacuum-UV properties of ge related centers in gamma irradiated silica
2002
Photochemical inhomogeneity in the reduction process of the optical activity related to Ge oxygen deficient point defects in silica, characterized by an absorption band centered at 5.15 v eV and two emission bands centered at 3.2 v eV and 4.3 v eV, have been investigated. We have made a comparative study of the stationary and time dependent photoluminescence under excitation in the UV (5 v eV) and in the vacuum-UV (7.4 v eV) ranges in natural silica samples with native and with n -irradiation bleached optical activity. Our measurements evidence that the same spectral features are observed in the native and in the irradiated samples, but for an intensity reduction in the irradiated ones. Mor…
Pulsed electron beam excited transient absorption in SrTiO3
2002
Abstract Transient absorption (TA) spectra and optical density relaxation kinetics in SrTiO3 (STO), STO–Nb and STO–V were studied. The electron polaron free or bound at intrinsic defect is suggested to be responsible for the TA band at ∼1.4 eV observed in STO. The band peaking below 0.75 eV in STO–Nb is proposed to be from Nb4+. The electron center V3+ or electron polaron bound in the vicinity of V4+ is responsible for the absorption band at 1.0 eV in STO–V. The absorption from hole polarons is suggested to be in the range 1.8–2.3 eV. It is shown that TA in pure STO at room temperature decays due to electron–hole polaron recombination.
Effect of annealing on Zn1−xCoxO thin films prepared by electrodeposition
2009
Polycrystalline thin films of Zn"1"-"xCo"xO with different cobalt (Co) content were grown on indium tin oxide (ITO) substrates by cathodic electrodeposition technique and subsequently annealed in air at 400^oC. The effect of annealing in their structural, optical and chemical properties has been characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman scattering and optical spectroscopy. Our measurements indicate that moderate annealing increases the crystal quality of the films. The films are highly transparent in the visible range and evidence an increase of the band gap and of the intensity of three typical Co absorptio…
Ultraviolet-visible light-induced solarisation in silica-based optical fibres for indoor solar applications
2021
Abstract The transmission performances of pure- and doped-silica (a-SiO2) optical fibres are compared during the exposure to a high-power broadband light source approximating the solar spectrum. From the Gaussian decomposition of the attenuation spectra, we found that Al- and P-doped fibres show a fast solarisation effect which leads to transmission degradation in the ultraviolet-visible range. Similarly, Ge-doped fibres undergo photoinduced colour-centre formation which, however, does not prevent visible-light propagation. One of the two tested pure-silica fibres results completely unaffected by light exposure whereas the other shows an absorption band probably due to the presence of chlor…