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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: It is reported for the first time that the pure topological insulator Bi2Te3 exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation, which points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.
Abstract: Dirac-like topological insulators have attracted strong interest in optoelectronic application because of their unusual and startling properties. Here we report for the first time that the pure topological insulator Bi2Te3 exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation. The Bi2Te3 sheets with lateral size up to a few micrometers showed extremely low saturation absorption intensities of only 1.1 W/cm2 at 1.0 and 1.3 μm, respectively. Benefiting from this sensitive response, a Q-switching pulsed laser was achieved in a 1.0 μm Nd:YVO4 laser where the threshold absorbed pump power was only 31 mW. This is the lowest threshold in Q-switched solid-state bulk lasers to the best of our knowledge. A pulse duration of 97 ns was observed with an average power of 26.1 mW. A Q-switched laser at 1.3 μm was also realized with a pulse duration as short as 93 ns. Moreover, the mode locking operation was demonstrated. These results strongly exhibit that Bi2Te3 is a promising optical device for constructing broadband, miniature and integrated high-energy pulsed laser systems with low power consumption. Our work clearly points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.
46 citations
TL;DR: In this article, the main fragmentation channels were found to be loss of an atom or loss of a dimer, and the dissociation energies were extracted using a statistical model for the unimolecular decomposition following collisional excitation or photoexcitation.
46 citations
TL;DR: The relaxation dynamics of the dye D35 has been characterized by transient absorption spectroscopy in acetonitrile and on TiO (2) and ZrO(2) thin films, and there is no clear evidence for a transient Stark shift, which suggests that initially formed cation-electron (trap state) complexes do not dissociate to form mobile conduction band electrons.
Abstract: The relaxation dynamics of the dye D35 has been characterized by transient absorption spectroscopy in acetonitrile and on TiO2 and ZrO2 thin films. In acetonitrile, upon photoexcitation of the dye via the S0 → S1 transition, we observed ultrafast solvation dynamics with subpicosecond time constants. Subsequent decay of the S1 excited state absorption (ESA) band with a 7.1 ps time constant is tentatively assigned to structural relaxation in the excited state, and a spectral decay with 203 ps time constant results from internal conversion (IC) back to S0. On TiO2, we observed fast (<90 fs) electron injection from the S1 state of D35 into the TiO2 conduction band, followed by a biphasic dynamics arising from changes in a transient Stark field at the interface, with time constants of 0.8 and 12 ps, resulting in a characteristic blue-shift of the S0 → S1 absorption band. Several processes can contribute to this spectral shift: (i) photoexcitation induces immediate formation of D35˙+ radical cations, which initially form electron–cation complexes; (ii) dissociation of these complexes generates mobile electrons, and when they start diffusing in the mesoporous TiO2, the local electrostatic field may change; (iii) this may trigger the reorientation of D35 molecules in the changing electric field. A slower spectral decay on a nanosecond timescale is interpreted as a reduction of the local Stark field, as mobile electrons move deeper into TiO2 and are progressively screened. Multiexponential electron–cation recombination occurs on much longer timescales, with time constants of 30 μs, 170 μs and 1.4 ms. For D35 adsorbed on ZrO2, there is no clear evidence for a transient Stark shift, which suggests that initially formed cation–electron (trap state) complexes do not dissociate to form mobile conduction band electrons. Multiexponential decay with time constants of 4, 35, and 550 ps is assigned to recombination between cations and trapped electrons, and also to a fraction of D35 molecules in S1 which decay by IC to S0. Differential steady-state absorption spectra of D35˙+ in acetonitrile and dichloromethane provide access to the complete D0 → D1 band. The absorption spectra of D35 and D35˙+ are well described by TDDFT calculations employing the MPW1K functional.
46 citations
TL;DR: A Kelvin probe force microscopy study shows that chlorine incorporation can suppress the density of charged defects and thus enhances photoinduced bulk polarization due to the reduced screening effect from charged defects, and a bias-dependent photoluminescence study indicates that increasing bulk polarization can suppress carrier recombination by decreasing charge capture probability through the Coulombic screening effect.
Abstract: This article reports an experimental demonstration of photoinduced bulk polarization in hysteresis-free methylammonium (MA) lead-halide perovskite solar cells [ITO/PEDOT:PSS/perovskite/PCBM/PEI/Ag]. An anomalous capacitance–voltage (CV) signal is observed as a broad “shoulder” in the depletion region from −0.5 to +0.5 V under photoexcitation based on CV measurements where a dc bias is gradually scanned to continuously drift mobile ions in order to detect local polarization under a low alternating bias (50 mV, 5 kHz). Essentially, gradually scanning the dc bias and applying a low alternating bias can separately generate continuously drifting ions and a bulk CV signal from local polarization under photoexcitation. Particularly, when the device efficiency is improved from 12.41% to 18.19% upon chlorine incorporation, this anomalous CV signal can be enhanced by a factor of 3. This anomalous CV signal can be assigned as the signature of photoinduced bulk polarization by distinguishing from surface polarization...
46 citations
TL;DR: In this paper, the luminescence of interwell excitons in double quantum wells GaAs/AlGaAs (n-i-n heterostructures) with large-scale fluctuations of random potential in the heteroboundary planes was studied.
Abstract: The luminescence of interwell excitons in double quantum wells GaAs/AlGaAs (n-i-n heterostructures) with large-scale fluctuations of random potential in the heteroboundary planes was studied. The properties of excitons whose photoexcited electron and hole are spatially separated in the neighboring quantum wells were studied as functions of density and temperature within the domains on the scale less than one micron. For this purpose, the surfaces of the samples were coated with a metallic mask containing specially prepared holes (windows) of a micron size an less for the photoexcitation and observation of luminescence. For weak pumping (less than 50 μW), the interwell excitons are strongly localized because of small-scale fluctuations of a random potential, and the corresponding photoluminescence line is inhomogeneously broadened (up to 2.5 meV). As the resonant excitation power increases, the line due to the delocalized excitons arises in a thresholdlike manner, after which its intensity linearly increases with increasing pump power, narrows (the smallest width is 350 μeV), and undergoes a shift (of about 0.5 μeV) to lower energies, in accordance with the filling of the lowest state in the domain. With a rise in temperature, this line disappears from the spectrum (T
c
≤ 3.4 K). The observed phenomenon is attributed to Bose-Einstein condensation in a quasi-two-dimensional system of interwell excitons. In the temperature range studied (1.5–3.4 K), the critical exciton density and temperature increase almost linearly with temperature.
46 citations