Exciton

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

Nonanalyticity, Valley Quantum Phases, and Lightlike Exciton Dispersion in Monolayer Transition Metal Dichalcogenides: Theory and First-Principles Calculations.

Abstract: Exciton dispersion as a function of center-of-mass momentum Q is essential to the understanding of exciton dynamics. We use the ab initio GW-Bethe-Salpeter equation method to calculate the dispersion of excitons in monolayer MoS(2) and find a nonanalytic lightlike dispersion. This behavior arises from an unusual |Q|-term in both the intra- and intervalley exchange of the electron-hole interaction, which concurrently gives rise to a valley quantum phase of winding number two. A simple effective Hamiltonian to Q(2) order with analytic solutions is derived to describe quantitatively these behaviors.

Ultrafast spectroscopy of excitons in single-walled carbon nanotubes.

Abstract: We studied the femtosecond dynamics of photoexcitations in films containing semiconducting and metallic single-walled carbon nanotubes (SWNTs), using various pump-probe wavelengths and intensities We found that confined excitons and charge carriers with subpicosecond dynamics dominate the ultrafast response in semiconducting and metallic SWNTs, respectively Surprisingly, we also found from the exciton excited state absorption bands and multiphoton absorption resonances in the semiconducting nanotubes that transitions between subbands are allowed; this unravels the important role of electron-electron interaction in SWNT optics

Simultaneous enhancement of charge transport and exciton diffusion in poly(p-phenylene vinylene) derivatives

Abstract: Time-resolved luminescence spectroscopy has been used to investigate exciton diffusion in thin films of poly($p$-phenylene vinylene) (PPV)--based derivatives. Due to chemical modifications the PPV derivatives differ by three orders of magnitude in charge carrier mobility as a result of a reduced energetic disorder. From the photoluminescence decay curves of PPV/fullerene heterostructures, the exciton diffusion coefficient was found to increase by one order of magnitude with decreasing disorder. This increase in the diffusion coefficient is compensated by a decrease of the exciton lifetime, leading to an exciton diffusion length of $5--6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ for the various PPV derivatives.

Evidence for Fast Interlayer Energy Transfer in MoSe2/WS2 Heterostructures.

Abstract: Strongly bound excitons confined in two-dimensional (2D) semiconductors are dipoles with a perfect in-plane orientation. In a vertical stack of semiconducting 2D crystals, such in-plane excitonic dipoles are expected to efficiently couple across van der Waals gap due to strong interlayer Coulomb interaction and exchange their energy. However, previous studies on heterobilayers of group 6 transition metal dichalcogenides (TMDs) found that the exciton decay dynamics is dominated by interlayer charge transfer (CT) processes. Here, we report an experimental observation of fast interlayer energy transfer (ET) in MoSe2/WS2 heterostructures using photoluminescence excitation (PLE) spectroscopy. The temperature dependence of the transfer rates suggests that the ET is Forster-type involving excitons in the WS2 layer resonantly exciting higher-order excitons in the MoSe2 layer. The estimated ET time of the order of 1 ps is among the fastest compared to those reported for other nanostructure hybrid systems such as c...

Exciton Formation, Relaxation, and Decay in PCDTBT

Abstract: The nature and time evolution of the primary excitations in the pristine conjugated polymer, PCDTBT, are investigated by femtosecond-resolved fluorescence up-conversion spectroscopy. The extensive study includes data from PCDTBT thin film and from PCDTBT in chlorobenzene solution, compares the fluorescence dynamics for several excitation and emission wavelengths, and is complemented by polarization-sensitive measurements. The results are consistent with the photogeneration of mobile electrons and holes by interband π−π* transitions, which then self-localize within about 100 fs and evolve to a bound singlet exciton state in less than 1 ps. The excitons subsequently undergo successive migrations to lower energy localized states, which exist as a result of disorder. In parallel, there is also slow conformational relaxation of the polymer backbone. While the initial self-localization occurs faster than the time resolution of our experiment, the exciton formation, exciton migration, and conformational changes ...