Enhancing redshift phenomenon in time-resolved photoluminescence spectra of AlGaN epilayer

AlGaN epitaxial layer has been studied by means of temperature-dependent time-integrated photoluminescence（PL）and time-resolved photoluminescence（TRPL）. An enhancing redshift phenomenon in TRPL spectra with increasing temperature was observed, and the localized excitons behaved like quasi two-dimensional excitons between 6 K and 90 K. We demonstrated that these behaviors are caused by a change in the carrier dynamics with increasing temperature due to the competition of carriers＇ localization and delocalization in the AlGaN alloy.

Deposition of Ag Nanoparticles on Carbon Microspheres Surface：Evaluation of Structures,Electrochemical and Optical Properties

A hybrid material of carbon microspheres（CMSs） with Ag decoration（Ag/CMSs） was developed.Poly（3-hexylthiophene）：Ag/CMSs composite film was prepared by spin-coating.Scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectrometry,X-ray diffraction,thermogravimetric analysis and cyclic voltammetry were employed to analyze the morphologies,structures,thermal properties and energy levels of Ag/CMSs.The optical property of the composite films was characterized by ultraviolet-visible spectrophotometry and fluorescent spectrometry.The results indicate that silver nanoparticles（AgNPs,d = 10-20 nm） are distributed on the surface of CMSs.LUMO and HOMO energy levels of Ag/CMSs are-3.97 and-5.52 e V,below the vacuum energy level,respectively,indicating that it is feasible to use Ag/CMSs as an electron acceptor.Ag NPs are blended into the active layer to trigger localized surface plasmon resonance,and consequently enhance light harvesting.The coupling of surface plasmons and excitons increased the probability of exciton dissociation.

Exciton luminescence and many-body effect of monolayer WS2 at room temperature

Monolayer transition metal dichalcogenides favor the formation of a variety of excitonic quasiparticles,and can serve as an ideal material for exploring room-temperature many-body effects in two-dimensional systems.Here,using mechanically exfoliated monolayer WS;and photoluminescence(PL)spectroscopy,exciton emission peaks are confirmed through temperature-dependent and electric-field-tuned PL spectroscopy.The dependence of exciton concentration on the excitation power density at room temperature is quantitatively analyzed.Exciton concentrations covering four orders of magnitude are divided into three stages.Within the low carrier concentration stage,the system is dominated by excitons,with a small fraction of trions and localized excitons.At the high carrier concentration stage,the localized exciton emission from defects coincides with the emission peak position of trions,resulting in broad spectral characteristics at room temperature.