Topic
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: It was found that, upon photoexcitation, there is an ultrafast charge localization to an intramolecular charge-transfer (ICT) state, followed by the presence of a solvent and conformationally relaxed ICT state in these branched systems.
Abstract: Novel alkene and alkyne branched structures have been synthesized, and their two-photon absorption (2PA) properties are reported. This series of alkene and alkyne trimer systems tests the mechanistic approach for enhancing the 2PA process which is usually dictated by the pi-bridging, delocalization length, and corresponding charge transfer on the 2PA cross sections. The results suggest that alkene branched systems have higher 2PA cross sections. While steady-state absorption and emission measurements were not successful in predicting the observed trend of 2PA cross sections, time-resolved measurements have explained the trends observed. It was found that, upon photoexcitation, there is an ultrafast charge localization to an intramolecular charge-transfer (ICT) state, followed by the presence of a solvent and conformationally relaxed ICT state in these branched systems.
230 citations
TL;DR: In this paper, the utility of angular resolved photoemission with synchrotron radiation to determine the bonding configuration of adsorbed molecules was demonstrated, based on an understanding of the gas phase phase photoexcitation of the molecule and making specific use of the polarized and continuum nature of the photon source to investigate the angle resolved emission from the adsorbate.
228 citations
TL;DR: In this article, a long-lifetime photoconductivity effect was observed in Te−doped Ga1−xAlxAs (0.25≲x≲0.7).
Abstract: A long‐lifetime (τ∼hours, T≲60 °K) photoconductivity effect is observed in Te‐doped Ga1−xAlxAs (0.25≲x≲0.7). Analysis of Hall‐effect data showing a pronounced decrease in the electron mobility upon photoexcitation shows that a donor level is involved. Similar effects are observed in Se‐ and Sn‐doped Ga1−xAlxAs (x=0.3). The magnitude of the effect which is typically of the order of the room‐temperature electron concentration seems to correlate linearly with the concentration of Te, showing that a constant concentration background impurity is not responsible for this effect. A large lattice relaxation is indicated by the large difference between the thermal (0.12 eV) and optical (1.1 eV) ionization energy of the donor level. The potential barrier to electron capture by the donor level is estimated to be 180 meV (x=0.36) from time decay measurements of the photoexcited electron population at low temperatures. Extrapolation to room temperature gives a characteristic decay time of ∼0.5 nsec for the electron concentrations expected in injection lasers.
228 citations
TL;DR: In this article, it has been shown that at relatively low intensities (5 W/cm 2 for GaAs) the photoexcited carrier distribution is Maxwellian with a carrier temperature T e different from the lattice temperature.
Abstract: It has become well established during the last few years that intense photoexcitation of a semiconductor leads to the heating of the carriers and the generation of nonequilibrium phonons. These phenomena which result from the relaxation of photoexcited carriers to the band extrema by interaction with other carriers and by emission of phonons, are reviewed in this paper. At relatively low intensities ( 5 W/cm 2 for GaAs) the photoexcited carrier distribution is Maxwellian with a carrier temperature T e different from the lattice temperature. T e as high as 150K and effective phonon temperatures as high as 3700K have been observed in GaAs. The observed variation of T e with excitation intensity leads to the conclusion that in semiconductors like GaAs the polar optical mode scattering is the dominant energy loss mechanism from the electron gas to the lattice. Similar results are obtained in CdSe and CdS. At higher intensities (>10 5 W/cm 2 for GaAs), the carrier dist0ribution becomes non-Maxwellian for reasons not well understood at present. We will also discuss some recent measurements of variation of T e with excitation wavelength and of the transmission spectra of photoexcited GaAs.
228 citations
TL;DR: In this article, the electronic and vibronic contributions to the two-photon absorption of a series of molecules with multi-branched structures have been studied using ab initio response theory.
Abstract: The electronic and vibronic contributions to the two-photon absorption of a series molecules with multi-branched structures have been studied using ab initio response theory. The results indicate that the electronic coupling between different branches alone cannot explain the experimental finding of a strong enhancement of the two-photon absorption cross section over the single branch structure, whereas it is predicted that vibronic contributions can play an important role in this respect. It is shown that for multi-branched molecules the use of circularly polarized light can increase the two-photon absorption cross section by a factor of 1.5 over linearly polarized light excitation.
226 citations