Search results for "Oscillator strength"
showing 10 items of 26 documents
Reversed polarized emission in highly strained a-plane GaN/AlN multiple quantum wells
2010
The polarization of the emission from a set of highly strained $a$-plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite $c$ axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the $c$ axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been p…
<title>Iodine and bromine resonance lamps in atmospheric research</title>
2003
For the first time previously developed iodine resonance spectra source has been tested in flash photolysis experiment. Quantitative measurements of concentration kinetics of iodine atomic species in a I2+O3 system are possible. The 183.038 nm resonance absorption transition of I(2P3/2) in previously developed EDL has been studied; dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume has been measured. The search for optimal conditions for an iodine EDL with minimized self-absorption and sufficient intensity were made. In condition of flash photolysis with previously described method it is possible to determine the emission temperature, oscillat…
Optically Detected Magnetic Resonance of Chlorophyll Triplet States in Water-Soluble Chlorophyll Proteins from Lepidium virginicum: Evidence for Exci…
2018
Optically detected magnetic resonance of triplet states populated by photoexcitation in water-soluble chlorophyll proteins (WSCPs) from Lepidium virginicum has been performed using both absorption and fluorescence detection. Well resolved triplet-singlet (T-S) spectra have been obtained and interpreted in terms of electronic interactions among the four chlorophylls (Chls), forming two dimers in the WSCP tetramer. Localization of the triplet state on a single Chl leads to a redistribution of the oscillator strength in the remaining three Chls of the complex. By comparing the spectra with those obtained on a substoichiometric WSCP complex containing only 2 Chls per protein tetramer, we proved…
Spectroscopic parameters related to non bridging oxygen hole centers in amorphous-SiO2
2005
The relationship between the luminescence at 1.9 eV and the absorption bands at 2.0 eV and at 4.8 eV were investigated in a wide variety of synthetic silica samples exposed to different gamma- and beta-ray irradiation doses. We found that the intensities of these optical bands are linearly correlated in agreement with the model in which they are assigned to a single defect. This finding allows to determine spectroscopic parameters related to optical transitions efficiency: the oscillator strength of the 4.8 eV results ~200 times higher than that of the 2.0 eV; the 1.9 eV luminescence quantum yield under 4.8 eV excitation is lower (by a factor ~3) than that under 2.0 eV excitation. These res…
Inner-shell excitation spectroscopy of closo-carboranes
1997
Oscillator strength spectra in the region of B 1s and C 1s excitation of three isomeric carborane cage compounds [closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H...
Estimation of the emission temperature of an electrodeless discharge lamp and determination of the oscillator strength for the I(2P3/2) 183.038 nm re…
2001
Abstract The 183.038 nm resonance absorption transition of I( 2 P 3/2 ) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10 −3 mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using …
Oscillator strength reduction induced by external electric fields in self-assembled quantum dots and rings
2007
We have carried out continuous wave and time resolved photoluminescence experiments in self-assembled In(Ga)As quantum dots and quantum rings embedded in field effect structure devices. In both kinds of nanostructures, we find a noticeable increase of the exciton radiative lifetime with the external voltage bias that must be attributed to the field-induced polarizability of the confined electron hole pair. The interplay between the exciton radiative recombination and the electronic carrier tunneling in the presence of a stationary electric field is therefore investigated and compared with a numerical calculation based on the effective mass approximation.
Optical properties of acceptor–exciton complexes in ZnO/SiO2 quantum dots
2011
Abstract The binding energy E b of the acceptor–exciton complex (A − ,X) as a function of the radius (or of the impurity position of the acceptor) and the normalized oscillator strength of (A − ,X) in spherical ZnO quantum dots (QDs) embedded in a SiO 2 matrix are calculated using the effective-mass approximation under the diagonalzation matrix technique, including a three-dimensional confinement of the carrier in the QD and assuming a finite depth. Numerical results show that the binding energy of the acceptor–exciton complexes is particularly robust when the impurity position of the acceptor is in the center of the ZnO QDs. It has been clearly shown from our calculations that these physic…
Optical absorption and electron paramagnetic resonance of theEα′center in amorphous silicon dioxide
2008
We report a combined study by optical absorption (OA) and electron paramagnetic resonance (EPR) spectroscopy on the E{sub {alpha}}{sup '} point defect in amorphous silicon dioxide (a-SiO{sub 2}). This defect has been studied in {beta}-ray irradiated and thermally treated oxygen-deficient a-SiO{sub 2} materials. Our results have pointed out that the E{sub {alpha}}{sup '} center is responsible for an OA Gaussian band peaked at {approx}5.8 eV and having a full width at half maximum of {approx}0.6 eV. The estimated oscillator strength of the related electronic transition is {approx}0.14. Furthermore, we have found that this OA band is quite similar to that of the E{sub {gamma}}{sup '} center in…
Optical properties of exciton confinement in spherical ZnO quantum dots embedded in matrix
2009
Abstract The optical characteristics of ZnO nanoparticles in SiO2 matrix have been determined by UV–visible and photoluminescence (PL) studies. The PL spectrum of the ZnO quantum dots shows two different bands: the first one is a broad green emission band related to deep level emission in the visible range and the second one is situated at 3.48 eV in the ultraviolet region, and is attributed to the recombination of electrons in the conduction band and holes in the valence band. The experimental result that we found was simulated numerically using different methods. Our calculations revealed a good agreement between the matrix element calculation method and the experimental result. We have a…