Photoluminescence of CdS nanoparticles suspended in vacuum and its temperature increase by laser irradiation

Abstract

We report here photoluminescence of CdS nanoparticles suspended in vacuum. The CdS nanoparticles, whose size distribution was bimodal having peaks at 11.3 and 43.1 nm, were produced by the gas-evaporation method and the nanoparticle beams were formed within the rarefied inert-gas flow. The band-edge emission and surface luminescence of the CdS nanoparticles, whose surfaces were completely free from adsorption, reaction or contamination with their surroundings, were observed. As the excitation intensity increased, the band-edge emission shifted to lower energy and the surface state luminescence shifted to higher energy. These energy shifts in the photoluminescence spectra as functions of excitation intensity were interpreted as an internal temperature rise of the CdS nanoparticles suspended in vacuum, and the internal temperature of the CdS nanoparticles was evaluated by means of photoluminescence. It was found that the nanoparticles suspended in vacuum were heated by much weaker laser irradiation than the bulk surface due to the large surface-to-volume ratio.