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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 article, a femtosecond time-resolved electroabsorption technique employing an AlGaN/GaN heterojunction p-i-n diode with a p-type Al-GaN window layer and a semitransparent p contact has been used to measure the transient electron velocity overshoot in GaN.
Abstract: A femtosecond time-resolved electroabsorption technique employing an AlGaN/GaN heterojunction p–i–n diode with a p-type AlGaN window layer and a semitransparent p contact has been used to measure the transient electron velocity overshoot in GaN. A peak transient electron velocity of 7.25×107 cm/s within the first 200 fs after photoexcitation has been observed at a field of 320 kV/cm. The increase in electron transit time across the device with increasing field beyond 320 kV/cm provides experimental evidence for a negative differential resistivity region of the steady-state velocity-field characteristic in this high field range.
61 citations
TL;DR: In this article, the radiative recombination of photoexcited carriers bound at native donors and acceptors in exfoliated nanoflakes of nominally undoped rhombohedral γ-polytype InSe was studied.
Abstract: We report on the radiative recombination of photo-excited carriers bound at native donors and acceptors in exfoliated nanoflakes of nominally undoped rhombohedral γ-polytype InSe. The binding energies of these states are found to increase with the decrease in flake thickness, L. We model their dependence on L using a two-dimensional hydrogenic model for impurities and show that they are strongly sensitive to the position of the impurities within the nanolayer.
61 citations
TL;DR: This study directly probes the mechanisms for enhanced hot electron generation and decay in a model plasmonic heterojunction by means of time-resolved two-photon photoemission (2PP) spectroscopy.
Abstract: Hot electron processes at metallic heterojunctions are central to optical-to-chemical or electrical energy transduction. Ultrafast nonlinear photoexcitation of graphite (Gr) has been shown to create hot thermalized electrons at temperatures corresponding to the solar photosphere in less than 25 fs. Plasmonic resonances in metallic nanoparticles are also known to efficiently generate hot electrons. Here we deposit Ag nanoclusters (NC) on Gr to study the ultrafast hot electron generation and dynamics in their plasmonic heterojunctions by means of time-resolved two-photon photoemission (2PP) spectroscopy. By tuning the wavelength of p-polarized femtosecond excitation pulses, we find an enhancement of 2PP yields by 2 orders of magnitude, which we attribute to excitation of a surface-normal Mie plasmon mode of Ag/Gr heterojunctions at 3.6 eV. The 2PP spectra include contributions from (i) coherent two-photon absorption of an occupied interface state (IFS) 0.2 eV below the Fermi level, which electronic structur...
61 citations
TL;DR: In this paper, it was shown that ethanol quenches valence-band holes within ∼15 ps of photoexcitation, but does not quench the trapped holes responsible for the characteristic visible photoluminescence of colloidal ZnO nanocrystals.
Abstract: Photochemical charging of colloidal ZnO nanocrystals has been studied using continuous-wave and time-resolved photoluminescence spectroscopies in conjunction with electron paramagnetic resonance spectroscopy. Experiments have been performed with and without addition of alcohols as hole quenchers, focusing on ethanol. Both aerobic and anaerobic conditions have been examined. We find that ethanol quenches valence-band holes within ∼15 ps of photoexcitation, but does not quench the trapped holes responsible for the characteristic visible photoluminescence of ZnO nanocrystals. Hole quenching yields “charged” nanocrystals containing excess conduction-band electrons. The extra conduction-band electrons quench visible trap-centered luminescence via a highly effective electron/trap-state Auger-type cross-relaxation process. This Auger process is prominent even under aerobic photoexcitation conditions, particularly when samples are not stirred. Charging also reduces exciton nonradiative decay rates, resulting in i...
61 citations
TL;DR: In this article, a photoexcitation of ground state Cs-Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers) was used for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (≳2 nm) semiconductor diode lasers.
Abstract: Lasing on the 62P1/2→62S1/2 (D1) resonance transition of atomic Cs at 894.3 nm has been realised in mixtures of Ar, ethane, and Cs vapour by the photoexcitation of ground state Cs–Ar collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers). The blue satellites of the alkali D2 lines provide a pathway for optically pumping atomic alkali lasers on the principal series (resonance) transitions with broad linewidth (≳2 nm) semiconductor diode lasers.
61 citations