Search results for "Absorption"
showing 10 items of 2701 documents
Numerical and experimental investigation of short Au nanorods
2014
The plasmonic properties of Au nanorods (NRs) have been investigated theoretically and experimentally, a system that is of high current interest in relation to various nanophotonics applications. The non-aligned NRs arrays were formed by a seed-mediated growth method that relies on the reduction of metal salt by a weak reduction agent in the presence of preformed metallic seed nanoparticles. We applied the finite-element method to calculations of absorption spectra from gold NRs supported in an aqueous solution. Comparison to experimentally measured spectra is found in a good agreement.
High Voltage Insulation and Gas Absorption of Polymers in High Pressure Argon and Xenon Gases
2018
High pressure gas time projection chambers (HPGTPCs) are made with a variety of materials, many of which have not been well characterized in high pressure noble gas environments. As HPGTPCs are scaled up in size toward ton-scale detectors, assemblies become larger and more complex, creating a need for detailed understanding of how structural supports and high voltage insulators behave. This includes the identification of materials with predictable mechanical properties and without surface charge accumulation that may lead to field deformation or sparking. This paper explores the mechanical and electrical effects of high pressure gas environments on insulating polymers PTFE, HDPE, PEEK, POM …
Linear and Angular Distyrylpyrazines with Terminal Donor Groups: Synthesis, Solvatochromism, and Acidochromism of the Electronic Spectra
2011
A series of linear and angular distyrylpyrazines and lateral donor groups has been prepared by aldol condensation between dimethylpyrazines and the appropriate aromatic aldehyde. The optical absorption and emission properties of these systems were studied in different solvents and media. The materials display a strong solvatochromism of the emission that is reflected by large red shifts of their fluorescence emission maxima on increasing the solvent polarity. This behaviour suggests a highly polar emitting state, which is characteristic of compounds that undergo an internal charge transfer upon excitation. Upon protonation, the UV-vis spectra are altered, and the fluorescence intensity of t…
Tuning the Direct and Indirect Excitonic Transitions of h-BN by Hydrostatic Pressure
2021
The pressure dependence of the direct and indirect bandgap transitions of hexagonal boron nitride is investigated using optical reflectance under hydrostatic pressure in an anvil cell with sapphire windows up to 2.5 GPa. Features in the reflectance spectra associated with the absorption at the direct and indirect bandgap transitions are found to downshift with increasing pressure, with pressure coefficients of −26 ± 2 and −36 ± 2 meV GPa–1, respectively. The GW calculations yield a faster decrease of the direct bandgap with pressure compared to the indirect bandgap. Including the strong excitonic effects through the Bethe–Salpeter equation, the direct excitonic transition is found to have a…
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.