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Exciton

About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.


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Journal ArticleDOI
TL;DR: In this paper, an upconversion from negatively charged to neutral excitons is observed in monolayer tungsten diselenide, which could provide a route for cooling two-dimensional semiconductors using lasers.
Abstract: An upconversion from negatively charged to neutral excitons is observed in monolayer tungsten diselenide, which could provide a route for cooling two-dimensional semiconductors using lasers.

209 citations

Journal ArticleDOI
16 Jan 2017
TL;DR: In this paper, low-temperature magneto-photoluminescence experiments were conducted to demonstrate the brightening of dark excitons by an in-plane magnetic field B applied to monolayers of different semiconducting transition metal dichalcogenides.
Abstract: We present low-temperature magneto-photoluminescence experiments which demonstrate the brightening of dark excitons by an in-plane magnetic field B applied to monolayers of different semiconducting transition metal dichalcogenides. For WSe2 and WS2 monolayers, the dark exciton emission is observed at??~50 meV below the bright exciton peak and displays a characteristic doublet structure whose intensity grows with B 2, while no magnetic field induced emission peaks appear for MoSe2 monolayer. Our experiments also show that the MoS2 monolayer has a dark exciton ground state with a dark-bright exciton splitting energy of??~100 meV.

208 citations

Journal ArticleDOI
24 Feb 2014-ACS Nano
TL;DR: An experimental investigation on the exciton dynamics of monolayer and bulk WSe2 samples, both of which are studied by femtosecond transient absorption microscopy, resolves the differential reflection signal in both time and space and deduces other parameters characterizing theexciton dynamics such as the diffusion length, the mobility, the mean free path, and themean free length.
Abstract: We present an experimental investigation on the exciton dynamics of monolayer and bulk WSe2 samples, both of which are studied by femtosecond transient absorption microscopy. Under the excitation of a 405 nm pump pulse, the differential reflection signal of a probe pulse (tuned to the A-exciton resonance) reaches a peak rapidly that indicates an ultrafast formation process of excitons. By resolving the differential reflection signal in both time and space, we directly determine the exciton lifetimes of 18 ± 1 and 160 ± 10 ps and the exciton diffusion coefficients of 15 ± 5 and 9 ± 3 cm2/s in the monolayer and bulk samples, respectively. From these values, we deduce other parameters characterizing the exciton dynamics such as the diffusion length, the mobility, the mean free path, and the mean free length. These fundamental parameters are useful for understanding the excitons in monolayer and bulk WSe2 and are important for applications in optoelectronics, photonics, and electronics.

208 citations

Journal ArticleDOI
TL;DR: In this paper, the properties of excitons in one-dimensional molecular aggregates, dissolved at room temperature in a liquid, were studied by means of femtosecond nonlinear optical experiments.
Abstract: The properties of excitons in one‐dimensional molecular aggregates, dissolved at room temperature in a liquid, were studied by means of femtosecond nonlinear optical experiments. Both the one‐exciton band (i.e., Frenkel‐excitons) and multiexciton bands contribute to the observed nonlinear optical response. The rapid motions in the liquid lead to ultrafast perturbations of the molecular energy levels. This localizes the excitons on limited sections of the chains of aggregated molecules. Ultrafast frequency‐resolved pump–probe spectroscopy on the lowest two exciton bands was employed to determine the delocalization length of the optical excitations. The kinetics of the exciton populations was measured by ultrafast grating scattering experiments and time‐resolved single photon counting. A model is described in which the multiexciton bands act as doorway states in the exciton–exciton annihilation process. These bands thereby determine the population decay of the Frenkel excitons at high excitation densities. Room temperature photon echo experiments show that stochastic perturbations of the exciton transition frequencies occur on two distinct time scales. In particular the slow components of the fluctuations are affected by motional narrowing, associated with the exciton delocalization length. It is therefore argued that the optical dephasing of excitons is directly related to the spatial extent of the excitation on the aggregate chain.

208 citations

Journal ArticleDOI
TL;DR: It is found that the frequency dispersion of the third-order nonlinear susceptibility of the biexciton binding energy and the oscillator strength shows an out-of-phase behavior at the one- and two-photon resonances, which is characteristic of the exciton and bIExciton transitions.
Abstract: Biexciton states in semiconductor quantum dots (spherical microcrystallites) are investigated variationally, and the biexciton binding energy and the oscillator strength are calculated as a function of the quantum-dot radius, the electron-to-hole mass ratio, and the dielectric constant ratio of the semiconductor to the surrounding medium. The most important mechanisms for enhancing the biexciton binding energy and the oscillator strength are clarified. One is the quantum confinement effect, which increases the spatial overlap between carriers, leading to enhanced Coulomb interaction. Another is the dielectric confinement effect due to the dielectric constant discontinuity at the interface between a semiconductor microcrystallite and the surrounding medium. This effect arises from the penetration of electric force lines through the surrounding medium with a relatively small dielectric constant and leads to an enhancement of the Coulomb interaction. It is found that the frequency dispersion of the third-order nonlinear susceptibility ${\ensuremath{\chi}}^{(3)}$ shows an out-of-phase behavior at the one- and two-photon resonances, which is characteristic of the exciton and biexciton transitions. For typical materials which are promising for observation of the biexciton state in microcrystallites, the values of the biexciton binding energy, the third-order nonlinear susceptibility ${\ensuremath{\chi}}^{(3)}$, and the two-photon absorption coefficient ${K}_{2}$ of the biexciton state are predicted theoretically.

208 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,269
20222,623
20211,045
20201,157
20191,096
20181,057