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Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2
摘要： Photon upconversion is an anti-Stokes process in which an absorption of a photon leads to a reemission of a photon at an energy higher than the excitation energy. The upconversion photoemission has been already demonstrated in rare earth atoms in glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate a room temperature upconversion photoluminescence process in a monolayer semiconductor WS2, with energy gain up to 150 meV. We attribute this process to transitions involving trions and many phonons and free exciton complexes. These results are very promising for energy harvesting, laser refrigeration and optoelectronics at the nanoscale.
关键词： photoluminescence,monolayer semiconductor,phonons,energy gain,room temperature,WS2,excitons,trions,upconversion
更新于2025-09-23 15:22:29
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Probing exciton species in atomically thin WS<sub>2</sub>–graphene heterostructures
摘要： We report on a detailed study of temperature-dependent photoluminescence spectroscopy of monolayer WS2 grown on epitaxial graphene. The study reveals for the first time the intrinsic excitonic effects of WS2 supported on one- and two-layer graphene from room temperature to 83K, with both excitons and trions evidenced in the entire temperature range and temperature-independent trion dissociation. All emission peaks exhibit a shift towards higher energy with decreasing temperature due to band gap renormalisation induced by electron-phonon interaction. A highly linear dependence of the photoluminescence with the excitation power is found for both WS2 on one- and two-layer graphene, confirming the excitonic nature of associated transitions and the high crystal quality of the WS2-graphene heterostructure.
关键词： trions,2D heterostructures,excitons
更新于2025-09-23 15:22:29
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Occurrence control of charged exciton for a single CdSe quantum dot at cryogenic temperatures on an optical nanofiber
摘要： We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The present photo-charging method may open a new route to applying the CdSe quantum dots in quantum photonics, and the hybrid system of photocharged quantum-dot and optical nanofiber may readily be applicable to a fiber-in-line single-photon generator.
关键词： Optical nanofiber,Cryogenic temperatures,CdSe quantum dots,Photocharging,Trions
更新于2025-09-23 15:21:01
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Stark shift of excitons and trions in two-dimensional materials
摘要： The effect of an external in-plane electric ?eld on neutral and charged exciton states in two-dimensional (2D) materials is theoretically investigated. These states are argued to be strongly bound, so that electron-hole dissociation is not observed up to high electric ?eld intensities. Trions in the anisotropic case of monolayer phosphorene are demonstrated to be especially robust under electric ?elds, so that ?elds as high as 100 kV/cm yield no signi?cant effect on the trion binding energy or probability density distribution. Polarizabilities of excitons are obtained from the parabolicity of numerically calculated Stark shifts. For trions, a fourth order Stark shift is observed, which enables the experimental veri?cation of hyperpolarizability in 2D materials, as observed in the highly excited states of the Rydberg series of atoms and ions.
关键词： Stark shift,polarizability,two-dimensional materials,electric field,excitons,trions,hyperpolarizability
更新于2025-09-04 15:30:14