Search results for "absorption spectroscopy"
showing 10 items of 828 documents
Optical study of GeO2–PbO–PbF2 oxyfluoride glass singly doped with Pr3+, Nd3+, Sm3+ and Eu3+
2005
Abstract Glasses with composition 50GeO 2 –(50 − x )PbO–5PbF 2 – x LnF 3 (Ln = Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ ) were synthesised in the bulk form. The content of PbF 2 was constant and amounted to 5 mol% whereas, the concentration of luminescent ions was 0.2 and 2 mol%. Spectroscopic properties (absorption, emission) of optically active ions were studied at room temperature. Oscillator strengths have been used to calculate phenomenological intensity parameters Ω 2,4,6 . Radiative transition probabilities as well as branching ratios and radiative lifetimes of luminescent levels were estimated. Lifetimes and the fluorescence dynamics were studied as a function of concentration. The Judd–Ofelt…
Ultrafast Relaxation Dynamics of Osmium−Polypyridine Complexes in Solution
2013
We present steady-state absorption and emission spectroscopy and femtosecond broadband photoluminescence up-conversion spectroscopy studies of the electronic relaxation of Os(dmbp)(3) (Os1) and Os(bpy)(2)(dpp) (Os2) in ethanol, where dmbp is 4,4'-dimethyl-2,2'-biypridine, bpy is 2,2'-biypridine, and dpp is 2,3-dipyridyl pyrazine. In both cases, the steady-state phosphorescence is due to the lowest (MLCT)-M-3 state, whose quantum yield we estimate to be <= 5.0 x 10(-3). For Os1, the steady-state phosphorescence lifetime is 25 ns. In both complexes, the photoluminescence excitation spectra map the absorption spectrum, pointing to an excitation wavelength-independent quantum yield. The ultrafa…
Energy transport in silica to oxygen-deficient luminescence centers. Comparison with other luminescence centers in silica and α-quartz
2004
Abstract The transport of energy absorbed by silica glass to oxygen-deficient luminescence centers in was studied in the range of intrinsic absorption from 8.2 up to 35 eV. The low efficiency of exciting those luminescence centers by transport of energy could not be ascribed merely to carrier scattering by the disordered structure. Other centers (Cu + , for example) could be excited in such process with sufficiently high efficiency, albeit lower than that in crystals. The low efficiency of interaction of oxygen deficient centers with quasi-particles is attributed to isolation of these centers in clusters and the non-radiative annihilation of the quasi-particles on the boundaries of these cl…
Formation of optically active oxygen deficient centers in Ge-doped SiO2 by γ- and β-ray irradiation
2010
Abstract We report an experimental study on the comparison between the γ- or β-ray induced Ge related point defects in Ge-doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol–gel technique have been irradiated with γ-ray or with β-ray. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E’Ge, GLPC (Germanium lone pair center) and H(II) point defects. No relevant differences between the concentrations of γ- or β-ray induced Ge(1) and E’Ge point defects have been observed and, in addition, it ha…
Absorption and luminescence in amorphous silica synthesized by low-pressure plasmachemical technology
2007
A comparison study of as-deposited by the hydrogen-free SPCVD process silicon dioxide with and without fluorine as well as the one in the form of fused materials is performed to define whether glass forming processing affects its optical properties. Raman scattering, optical absorption in the vacuum ultraviolet region as well as luminescence at different temperatures and various excitation conditions are measured. A difference in Urbach rule parameters and intrinsic defect concentrations for different samples is revealed. No significant impact on the structure responsible for Raman scattering is observed.
Conformational disorder and optical properties of point defects in vitreous silica
2004
Abstract Disordered systems are characterized by the presence of local conformational heterogeneity, which reflects the complex landscape of the potential energy of the vitreous state. Optical properties of defects embedded in a vitreous matrix are also determined by the interaction with the surrounding environment; so the conformational disorder of the system induces spectral inhomogeneity. As a consequence, detailed experimental investigation of absorption and photoluminescence bands can give information on configurational substates around the chromophore. We focused our attention on B-type optical activity in silica glasses, characterized by a singlet emission and a triplet emission, conne…
Optical properties of thin films of ZnO prepared by pulsed laser deposition
2004
In this paper we report on the structural features and optical properties of wurtzite ZnO films epitaxially grown on sapphire, fluorite and mica substrates by means of pulsed laser deposition (PLD). Post-deposition annealing results in a clear improvement of the film quality, reflected by the small width of the exciton-related lines in both the absorption and the photoluminescence spectra. Photoluminescence spectra revealed a multi-line structure which is identified in term of free excitons and excitons complexes with neutral donors and deep centers. The relative intensity of the PL lines mainly depends on the nature of the substrate used. Concerning optoelectronic applications it is especi…
The evolution of the fraction of Er ions sensitized by Si nanostructures in silicon-rich silicon oxide thin films
2009
Photoluminescence (PL) and time-resolved PL experiments as a function of the elaboration process are performed on Er-doped silicon-rich silicon oxide (SRO:Er) thin films grown under NH(3) atmosphere. These PL measurements of the Er(3+) emission at 1.54 microm under non-resonant pumping with the Er f-f transitions are obtained for different Er(3+) concentrations, ranging from 0.05 to 1.4 at.%, and various post-growth annealing temperatures of the layers. High resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) analysis show a high density of Si nanostructures composed of amorphous and crystalline nanoclusters varying from 2.7 x 10(18) to 10(18) cm(-3) as a fun…
Growth and optical characterization of indirect-gap AlxGa1−xAs alloys
1999
Nonintentionally doped AlxGa1−xAs layers with 0.38 x 0.84 were grown on (100) GaAs substrates by liquid phase epitaxy (LPE) under near-equilibrium conditions. The crystalline quality of the samples was studied by photoluminescence at 2 K and room temperature Raman spectroscopy. The peculiar behavior in the photoluminescence intensities of the indirect bound exciton line and the donor–acceptor pair transition is explained from the evolution of the silicon donor binding energy according to the aluminum composition. It was also possible to observe the excitonic transition corresponding to the AlxGa1−xAs/GaAs interface, despite the disorder and other factors which are normally involved when gro…
Study of the germanium luminescence in silica: from non-controlled impurity to germano-silicate core of telecommunication fiber preforms
2003
Abstract We have studed luminescence properties of doped silica with different concentrations of germanium. The basic luminescence parameters such as spectral dependencies, decay kinetics and polarization at different temperatures were measured. Three spectral ranges 3.5–5.5 eV(I), 5.5–7 eV(II), 7–8 eV(III) in the optical transparency range of silica could be chosen from these data. Range I possesses a weak variation of basic parameters of luminescence of the germanium related oxygen deficient center with the change of luminescence center concentration from extremely low in pure silica to the germano-silica core of optical telecommunication fiber preforms. The temperature dependence of lumi…