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Photoexcitation

About: Photoexcitation is a research topic. Over the lifetime, 5874 publications have been published within this topic receiving 134733 citations.


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TL;DR: In this paper, the Stieltjes-Tchebycheff moment method was used to calculate the total and partial-channel photoexcitation and ionization cross sections in carbon dioxide.
Abstract: Theoretical studies are reported of total and partial-channel photoexcitation and ionization cross sections in carbon dioxide. As in previously reported studies of discrete and continuum dipole spectra in diatomic (N2, CO, O2, F2) and polyatomic (H2O, H2CO, O3) molecules in this series, separated-channel static-exchange calculations of vertical-electronic transition energies and oscillator strengths and Stieltjes-Tchebycheff moment methods are employed in the development. Detailed comparisons are made of the static-exchange excitation and ionization spectra with photoabsorption, electron-impact excitation, and quantum-defect estimates of discrete transition energies and intensities, and with partial-channel photoionization cross sections obtained from fluorescence measurements and from tunable-source and (e,2e) photoelectron spectroscopy. The spectral characteristics of the various discrete series and continua are interpreted in terms of contributions from compact 2πu(π*), 5σg(σ*), and 4σu(σ*) virtual valence orbitals, and from more diffuse discrete and continuum Rydberg orbitals. The 2πu(π*) orbital is found to contribute to discrete excitation series, whereas the 5σg (σ*) and 4σu (σ*) orbitals generally appear in the photoionization continua as resonance-like diabatic valence features. Good agreement obtains between the calculated discrete excitation series and the results of a recent analysis of the available spectroscopic data. The calculated outer-valence-shell (1πg-1)X 2Πg, (1πu-1)A 2Πu, (3σu-1)B 2Σu+, and (4σg-1)C 2Σg+ partial-channel photoionization cross sections are in good accord with measured values, and clarify completely the origins of the various structures in the observed spectra. There is evidence, however, of coupling among scattering states associated with 1πg-1 and 1πu-1 ionic channels, giving rise to moderate disagreement with tunable-source photoelectron and fluorescence measurements over a portion of the spectrum. In the inner-valence-shell region, the calculated 2σu-1 and 3σg-1 cross sections are in qualitative accord with the observed many-electron spectral intensities, and provide a basis for quantitative interpretation when combined with appropriate intensity-borrowing calculations. The calculated carbon and oxygen K-edge cross sections are in good agreement with available cross sections obtained from electron-impact and photoabsorption measurements. It is of particular interest to find the oxygen K-edge (1σg-1, 1σu-1) cross section exhibits both the expected 5σg(σ*) and 4σu(σ*) resonance-like features. Finally, comparisons are made throughout of the discrete and continuum spectra in carbon dioxide with the results of previously reported studies in CO and O2, and the origins of the similarities and differences in the cross sections in these cases are clarified.

92 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the photoluminescence of films of poly-p$-phenylenevinylene (PPV) and changes of its intensity under conditions of electron spin resonance as a function of temperature and light intensity.
Abstract: Photoluminescence of films of poly-$(p$-phenylenevinylene) (PPV), and changes of its intensity under conditions of electron spin resonance as a function of temperature and light intensity were studied. The experimental technique was based on the modulation of the spin state of paramagnetic species by resonant microwave transitions between Zeeman sublevels of dynamically spin-polarized pairs. Three types of resonant signals were found in the magnetic resonance spectrum: (i) a narrow (1.7 mT width at the half height), (ii) a broad (140 mT) enhancement signal at $g$=2, and (iii) the signal at $g$=4. The results permitted one to conclude that Coulomb bound polaron pairs are produced in PPV with high yield under 488-nm photoexcitation. The narrow signal is assumed to appear due to microwave-induced resonant transitions in triplet polaron pairs. This implies that the resonant transitions change the rate of geminate recombination of the pairs that leads to the formation of triplet intrachain excitons. Those excitons annihilate in the second-order reaction and show themselves in the intensity of the photoluminescence. The annihilation rate was found to be influenced by resonant transitions in triplet exciton pairs as well and resulted in broad and $g$=4 signals. The lifetime of triplet intrachain excitons was estimated from microwave modulation frequency dependence of resonant signal intensities. The results showed that the energy level of the lowest polaron pair state situated below that of singlet intrachain exciton can act as a sink of the excitation energy influencing the quantum yields of the photoluminescence, electroluminescence, and photoconductivity.

92 citations

Journal ArticleDOI
TL;DR: The simulation results provide a basis for understanding several spectroscopic observations at molecular levels, including ultrafast dynamic Stokes shift, multicomponent fluorescence, viscosity dependence of the fluorescence lifetime, and radiationless decay from electronically excited state to the ground state along the isomerization coordinate.
Abstract: Detailed simulation study is reported for the excited-state dynamics of photoisomerization of cis-tetraphenylethylene (TPE) following excitation by a femtosecond laser pulse. The technique for this investigation is semiclassical dynamics simulation, which is described briefly in the paper. Upon photoexcitation by a femtosecond laser pulse, the stretching motion of the ethylenic bond of TPE is initially excited, leading to a significant lengthening of ethylenic bond in 300 fs. Twisting motion about the ethylenic bond is activated by the energy released from the relaxation of the stretching mode. The 90 degrees twisting about the ethylenic bond from an approximately planar geometry to nearly a perpendicular conformation in the electronically excited state is completed in 600 fs. The torsional dynamics of phenyl rings which is temporally lagging behind occurs at about 5 ps. Finally, the twisted TPE reverts to the initial conformation along the twisting coordinate through nonadiabatic transitions. The simulation results provide a basis for understanding several spectroscopic observations at molecular levels, including ultrafast dynamic Stokes shift, multicomponent fluorescence, viscosity dependence of the fluorescence lifetime, and radiationless decay from electronically excited state to the ground state along the isomerization coordinate. (C) 2007 American Institute of Physics.

92 citations

Journal ArticleDOI
Xin Han1, Dongyu Xu1, Lin An1, Hou Chengyi1, Yaogang Li1, Qinghong Zhang1, Hongzhi Wang1 
TL;DR: WO3/g-C3N4 two-dimensional composite photocatalysts were prepared through a simple hydrothermal method followed by a post thermal treatment in this paper, which showed that the orthorhombic-phase WO3 nanoparticles with a grain size from 5 to 80nm were successfully anchored on g-C 3N4 nanosheets surface with intimate contact.

92 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023249
2022529
2021221
2020204
2019183
2018256