Search results for "Electromagnetic radiation"
showing 10 items of 755 documents
ExTTF-Based Dyes Absorbing over the Whole Visible Spectrum
2011
International audience; New push−pull dyes featuring π-extended tetrathiafulvalene (exTTF) as the donor group and tricyanofuran (TCF) as the acceptor group were synthesized and characterized. Their broad absorption covers the entire visible spectral range and enters the near-infrared region. Electrochemistry and theoretical calculations provided an understanding of these singular electronic properties. The new dyes are appealing candidates as light harvesters in photovoltaic devices.
Subpicosecond Laser Spectroscopy of Blue-Light-Induced Absorption in KNbO3 and LiNbO3
2000
Pulses of 427-nm light from am amplified Ti:sapphire frequency-doubled laser are absorbed in two-photon band-gap excitations of KNbO3 and LiNbO3. Induced absorption spectra measured in the visible and recently extended in the infrared have been recorded as a function of delay from 0 to 250 ps after two-photon blue excitation. Samples include stoichiometric as well as congruent LiNbO3. Comparison is made to transient absorption in the nanosecond and longer time range induced by electron pulses of~10 ns width and 270 keV energy. Parts of the absorption can be attributed to bound and free polarons, including the intrinsic electron polaron.
Density Functional Theory Modelled Absorption and Raman Spectra Applicable to Ergocalciferol (Vitamin D2) and Cholecalciferol (D3)
2021
The study establishes optically relevant lines by modelling ergocalciferol (D2) and cholecalciferol (D3) and compare these to measured and earlier reported absorption and Raman spectra lines. This is a step to reach a further goal of finding if minute Vitamin D (D2 and D3) concentration changes could be determined so that a non-invasive sensor could be developed with a reference to non-invasive measurements reported in [1] describing a Raman spectroscopy method of blood glucose concentration of threshold of 5 mmol/l. However, our concentrations are lower by two orders, i.e., 50 nmol/l. At such concentrations random-type metabolites may have an important role, like those related with person’…
Transient attosecond soft-X-ray spectroscopy in layered semi-metals (Conference Presentation)
2020
X-ray absorption fine-structure (XAFS) spectroscopy is a well-established technique capable of extracting information about a material’s electronic and lattice structure with atomic resolution. While the near-edge region (XANES) of a XAFS spectrum provides information about the electronic configuration, structural information is extracted from the extended XAFS (EXAFS) spectrum, consisting of several hundreds of eV above the absorption edge. With the advent of high harmonic sources, reaching photon energies in soft x-ray (SXR) region, it now becomes possible to connect the spectroscopic capabilities of XAFS to the unprecedented attosecond temporal resolution of a high harmonic source allowi…
Light-Scattering and -Absorption of Nanoparticles
2012
To understand the optical response of nanoparticles to the incident light, a theoretical description is needed, which is given in this chapter. In a first approximation, these optical properties can be described using a quasi-static model, which assumes a particle-size much smaller than the wavelength of the light. The derivation of the polarizability of a sphere, which describes its optical properties, and further extensions for spheroidal, rod-shaped and coated particles are given in Sect. 2.2.
Transmission-line model to analyze a multistage polarizer rotator
1991
A simple transmission-line model to design a broadband system consisting of a multilayered polarization rotator that rotates the polarization plane of a linearly polarized electromagnetic wave is presented. A simulation program that permits the design of the rotator parameters was implemented, and a prototype was designed, manufactured, and tested. Comparisons between the theoretical results and measurements are given, and a good correspondence is found.
Multi-Resolution error analysis of predicted absorption coefficients. Method and application to the infrared spectrum of methane at high temperature.
2010
La version V2 inclut les modifications proposées par les reviewers.; International audience; A general method for the estimation of the confidence interval of molecular absorption coefficients is presented. Statistical numerical experiments are implemented to quantify the propagation of errors from line parameters to absorption coefficients or cross-sections as a function of the resolution. The method uses line parameter predictions (position and intensity) with estimated uncertainties derived from global polyad models. This work is especially intended to provide expert information for applications requiring theoretical predictions for which the present state of the art of line by line high…
Guidelines for the assessment of the rate law of slurry photocatalytic reactions
2017
Abstract The assessment of the rate law of slurry photocatalytic reactions appears to be a hard task, mainly because in this type of reactions the average rate of reaction, which is experimentally observed in a real reactor, could be very different from the “true” (intrinsic) rate of reaction, which cannot be measured directly. In the present work, it is shown how a proper mathematical model allows the utilization of the differential and/or the integral methods of kinetic analysis. The mathematical model must take into account not only the momentum and the mass balances, but also the radiative transfer equation. However, the discrimination among different proposed kinetic laws remains diffi…
Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures
2018
In this work, we have investigated the crystalline-size dependence of optical absorption and photoluminescence emission of CH3NH3PbI3 films, which is necessary to identify the potential practical applications of the gadgets based on perovskite films. This study was carried out at low temperatures to minimize the extra complexity induced by thermal effects. The purpose was to clarify the origin of the dual emission peak previously reported in the literature. We found that the grain size is responsible for the appearance or disappearance of this dual emission on CH3NH3PbI3 at low temperatures, whereas we have inferred that the thickness of the perovskite layer is a much more important factor …
A reaction engineering approach to kinetic analysis of photocatalytic reactions in slurry systems
2016
Abstract The knowledge of the rate equation is fundamental for the assessment of the activity of the photocatalytic material and for the study, design and optimization of photocatalytic reactors. In the case of photocatalytic reactions, the local volumetric rate of photon absorption (LVRPA) affects the reaction rate and its inherently uneven distribution within a “slurry” reactor makes complex a correct kinetic analysis. In the present work it is shown which are the critical aspects of the kinetic analysis in slurry reactors and how to carry out photocatalytic experiments to minimize the misinterpretations of the experimental results. In particular, the influence of the type of illumination…