Topic
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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TL;DR: All the important energy levels of singlet excitons with odd and even parity, the onset of the continuum band, the two-electron (biexciton) states, and the two relevant triplet states are determined and good agreement exists with models involving electron correlation.
Abstract: We have studied electronic excited states in films of poly(p-phenylenevinylene) using picosecond transient and cw photomodulation, photoluminescence, and their excitation spectra, as well as electroabsorption spectroscopy. We have determined all the important energy levels of singlet excitons with odd and even parity, the onset of the continuum band, the two-electron (biexciton) states, and the two relevant triplet states, and show that good agreement exists with models involving electron correlation.
241 citations
TL;DR: A nanoengineering-based approach is demonstrated that provides control over EI while maintaining nearly constant emission energy in core–shell CdSe/CdS NCs with a variable shell width and can be applied to other nanostructures with variable electron–hole overlap.
Abstract: A strong electron-hole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up to tens of meV) splitting between optically active ('bright') and optically passive ('dark') excitons. This dark-bright splitting has a significant effect on the optical properties of band-edge excitons and leads to a pronounced temperature and magnetic field dependence of radiative decay. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. We show that the dark-bright splitting can be widely tuned by controlling the electron-hole spatial overlap in core-shell CdSe/CdS NCs with a variable shell width. In thick-shell samples, the EI energy reduces to <250 μeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300 K and magnetic fields up to 7 T. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electron-hole overlap.
241 citations
TL;DR: In this paper, the authors showed that the inherent optical tunability of single-walled carbon nanotubes, present in their structural diversity, allows them to generate room-temperature single-photon emission spanning the entire telecom band.
Abstract: Generating quantum light emitters that operate at room temperature and at telecom wavelengths remains a significant materials challenge. To achieve this goal requires light sources that emit in the near-infrared wavelength region and that, ideally, are tunable to allow desired output wavelengths to be accessed in a controllable manner. Here, we show that exciton localization at covalently introduced aryl sp3 defect sites in single-walled carbon nanotubes provides a route to room-temperature single-photon emission with ultrahigh single-photon purity (99%) and enhanced emission stability approaching the shot-noise limit. Moreover, we demonstrate that the inherent optical tunability of single-walled carbon nanotubes, present in their structural diversity, allows us to generate room-temperature single-photon emission spanning the entire telecom band. Single-photon emission deep into the centre of the telecom C band (1.55 µm) is achieved at the largest nanotube diameters we explore (0.936 nm). Single-photon emission with 99% purity is generated from sp3 defects in carbon nanotubes (CNTs) by optical excitation at room temperature. By increasing the CNT diameter from 0.76 nm to 0.94 nm, the emission wavelength can be changed from 1,100 nm to 1,600 nm.
240 citations
TL;DR: The molecular adsorption can modulate the light emission and electrical properties of 1L WS2 and open up many opportunities to manipulate the electrical and optical properties of two-dimensional TMDs, particularly important for developing optoelectronic devices for chemical and biochemical sensing applications.
Abstract: Monolayer (1L) semiconducting transition metal dichacogenides (TMDs) possess remarkable physical and optical properties, promising for a wide range of applications from nanoelectronics to optoelectronics such as light-emitting and sensing devices. Here we report how the molecular adsorption can modulate the light emission and electrical properties of 1L WS2. The dependences of trion and exciton emission on chemical doping are investigated in 1L WS2 by microphotoluminescence (μPL) measurements, where different responses are observed and simulated theoretically. The total PL is strongly enhanced when electron-withdrawing molecules adsorb on 1L WS2, which is attributed to the increase of the exciton formation due to charge transfer. The electrical transport measurements of a 1L WS2 field effect transistor elucidate the effect of the adsorbates on the conductivity, which give evidence for charge transfer between molecules and 1L WS2. These findings open up many opportunities to manipulate the electrical and o...
240 citations
TL;DR: In this paper, a quasi-2D model was proposed to evaluate the role of screening on 2D hydrogenic excitons, where electrons and holes are described as point charges with a finite extension in the perpendicular direction and their interaction is screened by a dielectric function with a non-linear q-dependence which is computed ab-initio.
Abstract: The existence of strongly bound excitons is one of the hallmarks of the newly discovered atomically thin semi-conductors. While it is understood that the large binding energy is mainly due to the weak dielectric screening in two dimensions (2D), a systematic investigation of the role of screening on 2D excitons is still lacking. Here we provide a critical assessment of a widely used 2D hydrogenic exciton model which assumes a dielectric function of the form {\epsilon}(q) = 1 + 2{\pi}{\alpha}q, and we develop a quasi-2D model with a much broader applicability. Within the quasi-2D picture, electrons and holes are described as in-plane point charges with a finite extension in the perpendicular direction and their interaction is screened by a dielectric function with a non-linear q-dependence which is computed ab-initio. The screened interaction is used in a generalized Mott-Wannier model to calculate exciton binding energies in both isolated and supported 2D materials. For isolated 2D materials, the quasi-2D treatment yields results almost identical to those of the strict 2D model and both are in good agreement with ab-initio many-body calculations. On the other hand, for more complex structures such as supported layers or layers embedded in a van der Waals heterostructure, the size of the exciton in reciprocal space extends well beyond the linear regime of the dielectric function and a quasi-2D description has to replace the 2D one. Our methodology has the merit of providing a seamless connection between the strict 2D limit of isolated monolayer materials and the more bulk-like screening characteristics of supported 2D materials or van der Waals heterostructures.
239 citations