Search results for "absorption."
showing 10 items of 2682 documents
Photoluminescence in gamma-irradiated alpha-quartz investigated by synchrotron radiation
2004
Abstract We report an experimental investigation of the photoluminescence, under excitation by synchrotron radiation within the absorption band at 7.6 eV , induced in γ-irradiated α-quartz. Two emissions centered at 4.9 and 2.7 eV are observed at low temperature: the former decreases above 40 K , whereas the second band exhibits an initial slight increase and its quenching is effective above 100 K . Furthermore, the decay kinetics of both emissions occur in a time scale of nanoseconds: at T=17.5 K we measured a lifetime τ∼1.0 ns for the photoluminescence at 4.9 eV and τ∼3.6 ns for that at 2.7 eV . These results give new insight on the optical properties associated with defects peculiar of c…
Modeling the interactions between light and crystallizing polymer during fast cooling
2004
In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the ex- perimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evo- lution is proposed and applied to some fast cooling runs. The method was applied to q…
Transintestinal secretion of ciprofloxacin, grepafloxacin and sparfloxacin: in vitro and in situ inhibition studies.
2003
The influence of the secretion process on the absorption of ciprofloxacin, grepafloxacin and sparfloxacin has been evaluated by means of inhibition studies. Two well known P-glycoprotein inhibitors (cyclosporine, verapamil), a mixed inhibitor of P-glycoprotein and the organic cation transporter OCT1 (quinidine) and a well established MRP substrate (p-aminohipuric acid) have been selected in order to distinguish the possible carriers implicated. An in situ rat gut perfusion model and CACO-2 permeability studies are used. Both methods suggest the involvement of several types of efflux transporters for every fluoroquinolone. The relevance of the secretory pathway depends on the intrinsic perme…
Displacement Defect Formation in Complex Oxide Crystals under Irradiation
2000
The work is devoted to an analysis of formation processes of the radiation displacement defects (RDDs) and colour centres (CCs) in complex oxide crystals under irradiation. The calculation results on: the displacement process simulation as well as an analysis of the RDD and CC accumulation kinetics are presented. New experimental results on additional absorption spectra induced by neutron irradiation of LiNbO(3) (LNO) crystals doped with Fe and Cr and YAlO(3) (YAP) crystals doped with Nd and Er as well are presented. Dose dependencies of the additional absorption are compared and their peculiarities are discussed. The obtained results confirm that CCs causing the irradiation induced absorpt…
Cu Polyimidazole Thioether Complexes : Comparison of RDF's Reconstructed from XAFS and XRD Data
1997
Radial distribution functions (RDF) reconstructed from XAFS data (Cu K-edge at low and room temperatures) are compared with RDF's constructed from XRD crystallographic data of Cu polyimidazole thioether complexes. New EDA software package possibilities are used to reconstruct RDFs: (i) model independent RDF reconstruction, and (ii) multi shell - cumulant fitting. RDF's obtained from XRD data are broadened with Debye Waller factors calculated from XAFS. This way the structural disorder (set of distances) and thermal (vibrational) disorder are quantitatively taken into account in each RDF reconstruction approach. Within experimental error the three sets of RDF'S agree well with each other for…
Ion diffusion-controlled processes in fluoride crystals
2001
Ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF 2 , BaF 2 and LiBaF 3 crystals (X-ray irradiated at 290 K) have been investigated by means of ionic conductivity and the correlated ionic thermally stimulated depolarisation current (TSDC), and radiation-induced optical absorption band thermal bleaching techniques at 290-650 K. It was found that under a DC field fluorides store large ionic space-charge. In CaF 2 , BaF 2 and LiBaF 3 , by using the ionic TSDC technique we were able to detect a series of the interstitial anion and/or anion vacancy delocalisation stages in the extrinsic ionic conductivity region. At least 4-6 wide and overlapping ionic TSD…
Irradiation effects on the absorption edge of silica glass
2007
Abstract Vacuum ultraviolet absorption experiments were carried out on a variety of specimens of amorphous silica β-irradiated at different doses from ∼103 to 5 × 106 kGy. Changes in the width of the absorption (Urbach) edge were investigated. These changes strongly depend on the kind of silica considered: in particular the Urbach energy of silica of industrial manufacture increases in the irradiated samples, whereas in sol–gel silica it is poorly influenced by the irradiation. The fictive temperature of the different materials before and after irradiation was also monitored. The changes of the Urbach energy and of the fictive temperature are tentatively discussed considering the disorder d…
Interpretation of absorption edges by resonant electronic spectroscopy: experiment and theory
2004
Abstract Resonant electronic spectroscopy consists in measuring a non-radiative decay process (Auger or autoionization process) excited with photon energies around an absorption edge. The resonant spectra carry information both on the nature of the electronic transitions near the absorption edge by scanning the very first empty orbitals above the Fermi level (through the absorption process), and, on the other hand, on the atomic electronic configuration through the lineshape of the observed decay process. In this paper, after a quick review of the pioneering works in this field, we show that resonant measurements and their theoretical modeling can be used to precisely interpret complex abso…
Luminescence and ultraviolet excitation spectroscopy of SrI2 and SrI2:Eu2+
2013
Abstract We report measurements of luminescence and its ultraviolet excitation spectra in SrI2 and SrI2:Eu2+ at temperatures of 10 and 300 K. Attention is focused on determining the exciton energy and its temperature shift from features of the excitation spectra and limits placed by absorption spectroscopy on a 120 μm thin crystal, on observation of a broadened Eu emission band attributed to trace Eu associated with oxygen in nominally undoped crystals, and on adding observations concerning the 3.4 eV band at low temperature attributed by Pustovarov et al. to the self-trapped exciton.
Luminescence and transient absorption in ZnWO4 and ZnWO4–Fe crystals
2001
Abstract The transient absorption spectra and relaxation kinetics under pulse electron beam excitation in ZnWO 4 and ZnWO 4 –Fe, as well as luminescence spectra and decay kinetics, were studied. It is shown that a fraction of transient absorption is due to luminescence center excited state. The energy transfer from intrinsic excitations to the defect or impurity states is not efficient. The role of Fe-impurities in the decay process is discussed.