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Absorption (electromagnetic radiation)
About: Absorption (electromagnetic radiation) is a research topic. Over the lifetime, 76674 publications have been published within this topic receiving 1381221 citations.
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TL;DR: The organic component, presumably aromatic amino acids, is responsible for most or all of the observed optical absorption of dental enamel.
Abstract: The reflectance and transmission of thin slabs of dental enamel has been measured at all wavelengths between 220 and 700 nm by means of an integrating sphere. From the results the true scattering and absorption coefficients have been computed. The theoretical model used is an extended two-flux model, which is presented and discussed. The absorption spectrum of the dissolved organic component of enamel was also determined. An absorption peak at 270 nm is common to all the spectra. This peak in the bovine enamel spectrum is about three times as high as in the spectrum of human enamel. The peak of the dissolved material is about as high as the peak of the corresponding enamel. Hence it is concluded that the organic component, presumably aromatic amino acids, is responsible for most or all of the observed optical absorption.
189 citations
TL;DR: In this paper, the diffuse reflectance R of a powder is derived in general form in terms of the parameters of the individual particle, taking into account both internal and external scattering, and the relationship is compared with measurements on materials of different refractive indices.
Abstract: The optical properties of powders are determined for the case of particles, large compared with the wave‐length of light. The solution for the diffusion of light in a quasi‐infinitely thick powder is applied to relate certain measurements obtained on powders with the corresponding properties of the bulk material.In Part I, the diffuse reflectance R of a powder is first derived in general form in terms of the parameters of the individual particle, taking into account both internal and external scattering. Parameters are then obtained for a model for randomly shaped particles, and used to relate the diffuse reflectance to the optical absorption coefficient, the index of refraction, and the particle diameter. The relationship is compared with measurements on materials of different refractive indices.Part II deals with applications to luminescent powders, the calculation of the characteristics of emission in the presence of optical absorption, and the calculation of cascade transfer yields.
188 citations
TL;DR: In this article, the authors carried out laser-induced fluorescence measurements of hBN powder at room temperature under different environmental conditions (dry powder and suspensions in water or ethanol) and determined the absorption onset, related to the bandgap energy of this indirect gap semiconductor, has been precisely determined to be E g = 4.02±0.01 eV.
188 citations
TL;DR: The spectrum obtained by the Reflection Grating Spectrometer (RGS) exhibits broad (FWHM - 1400 km/s) absorption lines from highly ionized elements including hydrogen- and helium-like carbon, nitrogen, oxygen, and neon, and several iron L - shell ions (Fe XVII - XX).
Abstract: The luminous infrared-loud quasar IRAS 13349+2438 was observed with the XMM - Newton Observatory as part of the Performance Verification program. The spectrum obtained by the Reflection Grating Spectrometer (RGS) exhibits broad (FWHM - 1400 km/s) absorption lines from highly ionized elements including hydrogen- and helium-like carbon, nitrogen, oxygen, and neon, and several iron L - shell ions (Fe XVII - XX). Also shown in the spectrum is the first astrophysical detection of a broad absorption feature around lambda = 16 - 17 A identified as an unresolved transition array (UTA) of 2p - 3d inner-shell absorption by iron M-shell ions in a much cooler medium; a feature that might be misidentified as an O VII edge when observed with moderate resolution spectrometers. No absorption edges are clearly detected in the spectrum. We demonstrate that the RGS spectrum of IRAS 13349+2438 exhibits absorption lines from two distinct regions, one of which is tentatively associated with the medium that produces the optical/UV reddening.
188 citations
TL;DR: In this paper, single-walled carbon nanotubes (SWNTs) were compared with spectra from ensembles, showing that the peak shape and peak width are almost the same for a single nanotube as they are for the corresponding species in a large ensemble.
Abstract: Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are obtained from individual single-walled carbon nanotubes (SWNTs). Individual SWNT spectra are compared with spectra from ensembles. The PL spectrum of an individual SWNT in air at room temperature has a single asymmetric peak of width typically 10 to 15 meV, with no detected background. Both absorption and emission are strongly polarized along the tube axis. Photoluminescence excitation spectroscopy on single SWNTs clearly confirms the unique, one-to-one association of optical absorption resonances with individual emission peaks. Resonances in the PLE spectra are typically $\ensuremath{\approx}30\mathrm{meV}$ wide, with the PL intensity enhanced tenfold over nonresonant excitation. Whether for emission or absorption, the peak shape and peak width are almost the same for a single nanotube as they are for the corresponding species in a large ensemble. That is, there is no significant inhomogeneous broadening. While ensemble measurements are complicated by the superposition of many PL peaks from many different species, single nanotube spectra clearly isolate a single peak and are thus simpler to interpret.
188 citations