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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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Journal ArticleDOI
TL;DR: Results from UV-vis absorption study, Electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopic suggest that the improved photoactivity is due to a decrease in band gap energy, an increased light absorption in visible light region and possibly an enhanced electron-hole separation efficiency as a result of effective interfacial electron transfer between TiO2 and g-C3N4 of the g-N4/TiO2 composite film.

336 citations

Journal ArticleDOI
TL;DR: It is shown that the depth dependence of the distribution of photon absorption events can be inferred from measured parameters of the surface emission profile, and illustrative experimental data are shown to be in accord with the theory.
Abstract: Various characteristics of photon diffusion in turbid biological media are examined. Applications include the interpretation of data acquired with laser Doppler blood-flow monitors and the design of protocols for therapeutic excitation of tissue chromophores. Incident radiation is assumed to be applied at an interface between a turbid tissue and a transparent medium, and the reemission of photons from that interface is analyzed. Making use of a discrete lattice model, we derive an expression for the joint probability Γ(n, ρ)d2ρ that a photon will be emitted in the infinitesimal area d2ρ centered at surface point ρ = (x, y), having made n collisions with the tissue. Mathematical expressions are obtained for the intensity distribution of diffuse surface emission, the probability of photon absorption in the interior as a function of depth, and the mean path length of detected photons as a function of the distance between the site of the incident radiation and the location of the detector. We show that the depth dependence of the distribution of photon absorption events can be inferred from measured parameters of the surface emission profile. Results of relevant computer simulations are presented, and illustrative experimental data are shown to be in accord with the theory.

335 citations

Journal ArticleDOI
TL;DR: In systems that are two and three dimensional electronically, a large polaron and a small polaron are distinct types of quasiparticles, which depends on which electron-lattice interaction is of primary importance.
Abstract: In systems that are two and three dimensional electronically, a large polaron and a small polaron are distinct types of quasiparticles. The type of polaron formed depends on which electron-lattice interaction is of primary importance. A large polaron forms when the electron-lattice interaction due to the long-range Coulombic interactions between an electronic carrier and a solid's ions are of paramount importance. Competing effects then determine the radius of a large polaron. By contrast, a small polaron can form when a short-range electron-lattice interaction, such as the deformation-potential interaction, is dominant. A small polaron forms as its self-trapped carrier shrinks without limit until it is confined to a single site. Fundamental differences between large and small polarons produce optical spectra with distinguishing features. The absorption due to photoionization of a large polaron depends on products of the matrix elements for exciting a carrier from its self-trapped states to a free-carrier state and the density of these free-carrier states. These matrix elements fall sharply with increasing free-carrier wave vector k when kRg1, where R is the large polaron's radius. A large polaron's photoionization produces a temperature-independent absorption band. This band is asymmetric with the absorption intensity on the high-energy side of the peak exceeding that on the low-energy side of the peak.By contrast, the small-polaron absorption arises as the self-trapped carrier is induced to transfer from its well-localized state to a localized state at an adjacent site. Phonon broadening of these local electronic energy levels produces the widths of these absorption bands. Small-polaron absorption bands are asymmetric with the absorption intensity below the peak energy exceeding that above the peak energy. With rising temperature the phonon broadening of the local electronic energy levels progressively broadens these absorption bands. In addition, the motion of a polaron in response to an ac field can produce a (Drude-like) free-carrier absorption. A large polaron's free-carrier absorption occurs at frequencies below the characteristic phonon frequency. By contrast, if the narrow bands that characterize small polarons did not result in their localization, their coherent motion would produce a free-carrier absorption that is restricted to frequencies far below the phonon frequency. The optical spectra of large and small bipolarons are similar to those for large and small polarons, respectively. Finally, carrier-induced absorption bands observed in semiconducting and superconducting cuprates are compared with the expectations of large- and small-polaronic absorptions. The high-frequency absorption bands are consistent with the existence of large-polaronic carriers. However, taken together, the free-carrier absorptions and the dc transport in the superconductors depart from expectations of independent polaronic carriers. It is suggested that if the carriers in the cuprates are polaronic, their transport in the superconductors' normal states is collective.

335 citations

Journal ArticleDOI
TL;DR: In this article, the problem of the ac conductivity of a fully ionized plasma is investigated for frequencies embracing the plasma frequency, and the finite duration of encounters is taken into account in a self-consistent fashion which includes collective effects.
Abstract: The problem of the ac conductivity of a fully ionized plasma is investigated for frequencies embracing the plasma frequency. The finite duration of encounters is taken into account in a self‐consistent fashion which includes collective effects. The concomitant processes of absorption and emission of electromagnetic radiation are investigated and in particular the bremsstrahlung emission and absorption coefficients near the plasma frequency are given. The conversion of longitudinal to transverse waves by scattering from ions is discussed.

335 citations

Journal ArticleDOI
01 Sep 2006-Icarus
TL;DR: In this article, a suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance and structural relations for this group of minerals.

334 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2022185
20213,106
20202,866
20192,953
20182,876
20172,679