Search results for "absorption."
showing 10 items of 2682 documents
Optical and photovoltaic properties of indium selenide thin films prepared by van der Waals epitaxy
2001
Indium selenide thin films have been grown on p-type gallium selenide single crystal substrates by van der Waals epitaxy. The use of two crucibles in the growth process has resulted in indium selenide films with physical properties closer to these of bulk indium selenide than those prepared by other techniques. The optical properties of the films have been studied by electroabsorption measurements. The band gap and its temperature dependence are very close to those of indium selenide single crystals. The width of the fundamental transition, even if larger than that of the pure single crystal material, decreases monotonously with temperature. Exciton peaks are not observed even at low temper…
Untersuchungen zur Photoleitf�higkeit von alkoxysubstituierten Oligo- und Poly(1,4-phenylenethenylen)en
1994
Investigations on the Photoconductivity of Alkoxy Substituted Oligo- and Poly(1,4-phenyleneethenylene)s The photoreactivity and the photoconductivity of the mono- and dialkoxy substituted oligo- and poly(1,4-phenyleneethenylene)s 1/1′a-n were investigated in order to optimize the photoconducting properties of these materials. Increasing the length of the side chains enhances the average length of the main chain during the polycondensation and decreases the band gap till the limit of convergence is reached. The highest photoconductivity was observed for the 2,5-dipropyloxy system 1/1′j. Longer side chains render the charge transfer from chain to chain more difficult. The measurements were pe…
A Very Low Band Gap Diketopyrrolopyrrole-Porphyrin Conjugated Polymer
2017
International audience; A porphyrin-diketopyrrolopyrrole-containing polymer (poly(porphyrin-diketopyrrolopyrrole) (PPDPP)) shows impressive molar absorption coefficients from lambda=300 to 1000 nm. The photophysical and structural properties of PPDPP have been studied. With PPDPP as the electron donor and [ 6,6]phenyl C-71 butyric acid methyl ester (PC71BM) as the electron acceptor, the bulk heterojunction polymer solar cell showed overall power conversion efficiencies of 4.18 and 6.44% for as-cast and two-step annealing processed PPDPP: PC71BM (1: 2) active layers, respectively. These results are quite impressive for porphyrin-containing polymers, especially when directly included in the p…
Pressure effects on the electronic and optical properties ofAWO4wolframites (A =Cd, Mg, Mn, and Zn): The distinctive behavior of multiferroic MnWO4
2012
The electronic band-structure and band-gap dependence on the $d$ character of ${A}^{2+}$ cation in $A$WO${}_{4}$ wolframite-type oxides is investigated for different compounds ($A$ $=$ Mg, Zn, Cd, and Mn) by means of optical-absorption spectroscopy and first-principles density-functional calculations. High pressure is used to tune their properties up to 10 GPa by changing the bonding distances establishing electronic to structural correlations. The effect of unfilled $d$ levels is found to produce changes in the nature of the band gap as well as its pressure dependence without structural changes. Thus, whereas Mg, Zn, and Cd, with empty or filled $d$ electron shells, give rise to direct and…
Study of the bandgap renormalization in Ga-doped ZnO films by means of optical absorption under high pressure and photoelectron spectroscopy
2008
Abstract In this paper we investigate the band gap renormalization in heavily Ga-doped ZnO thin films deposited by pulsed laser deposition on C -plane sapphire and mica substrates. Thin films were studied by ultraviolet photoelectron spectroscopy and also by optical measurements under high pressure. The Fermi-level shift, as obtained from ultraviolet photoelectron experiments, exhibits a relatively small and positive shift (about 0.3 eV) with respect to the valence band for increasing electron concentrations up to 1021 cm−3. The optical gap exhibits a much larger increase (0.6 eV) for the same concentration range. Absorption measurements under pressure show that the pressure coefficient of …
Random Structural Modification of a Low-Band-Gap BODIPY-Based Polymer
2017
International audience; A BODIPY thiophene polymer modified by extending conjugation of the BODIPY chromophore is reported. This modification induces tunability of energy levels and therefore absorption wavelengths in order to target lower energies.
Functional response of novel bioprotective poloxamer-structured vesicles on inflamed skin
2017
[EN] Resveratrol and gallic acid, a lipophilic and a hydrophilic phenol, were co-loaded in innovative, biocompatible nanovesicles conceived for ensuring the protection of the skin from oxidative-and inflammatory-related affections. The basic vesicles, liposomes and glycerosomes, were produced by a simple, one-step method involving the dispersion of phospholipid and phenols in water or water/glycerol blend, respectively. Liposomes and glycerosomes were modified by the addition of poloxamer, a stabilizer and viscosity enhancer, thus obtaining viscous or semisolid dispersions of structured vesicles. The vesicles were spherical, unilamellar and small in size (similar to 70 nm in diameter). The …
Electronic Structure of Oxygen Dangling Bond in GlassySiO2: The Role of Hyperconjugation
2003
The electronic structure and the nature of optical transitions in oxygen dangling bond in silica glass, the nonbridging oxygen hole center (NBOHC), were calculated. The calculation reproduced well the peak positions and oscillator strengths of the well-known optical absorption bands at 2.0 and 4.8 eV, and of the recently discovered absorption band at 6.8 eV. The 2.0 eV band was attributed to transition from the $\ensuremath{\sigma}$ bond between Si and dangling oxygen to nonbonding $\ensuremath{\pi}$ orbital on the dangling oxygen. The uniquely small electron-phonon coupling associated with the 2.0 eV transition is explained by stabilization of Si-O bond in the excited state by hyperconjuga…
Er3+-doped GeGaSbS glasses for mid-IR fibre laser application: Synthesis and rare earth spectroscopy
2008
International audience; With an infrared transparency extended to 10 µm, low multiphonon relaxation rates and suitable rare earth solubility, sulphide glasses in the Ge-Ga-Sb-S system allow radiative emission from rare earth ions in the mid-IR range. The Er3+ ion, widely studied in glass fibres for optical amplification at 1.5 µm, presents an interesting transition for mid-IR applications around 4.5 µm (4I9/2→ 4I11/2). Thus, the aim of this work is to evaluate the Er3+-doped Ge20Ga5Sb10S65 glass as a potential fibre laser source operating in the 3-5 µm mid-IR spectral region. For that purpose, absorption and emission spectra were recorded from visible to mid-IR and the radiative lifetimes o…
Optical and Vibrational Spectra of CsCl-Enriched GeS2-Ga2S3 Glasses
2016
Optical and FTIR spectroscopy was employed to study the properties of 80GeS2-20Ga2S3-CsCl chalcohalide glasses with CsCl additives in a temperature range of 77–293 K. It is shown that CsCl content results in the shift of fundamental absorption edge in the visible region. Vibrational bands in FTIR spectra of (80GeS2-20Ga2S3)100 − х (СsCl) x (x = 5, 10, and 15) are identified near 2500 cm−1, 3700 cm−1,, around 1580 cm−1, and a feature at 1100 cm−1. Low energy shifts of vibrational frequencies in glasses with a higher amount of CsCl can be caused by possible thermal expansion of the lattice and nanovoid agglomeration formed by CsCl additives in the inner structure of the Ge-Ga-S glass.