Raman and photoluminescence study of CdSe nanoparticles capped with a bifunctional molecule

A series of cadmium selenide (CdSe) nanoparticles with rich cadmium ions capped with a bifunctional molecule, which contains both thiols and carboxylic acid groups has been prepared. Nanoparticles have been characterized by Raman, ultraviolet visible (UV–VIS) absorption and photoluminescence spectroscopy and X-ray diffraction (XRD). The Raman spectra showed that the surfactant molecules in the monolayer surrounding the CdSe nanoparticles are in a close-packed, crystalline state. Otherwise, the Cd ion on the nanoparticles surface can bind to both carboxylate and thiolate ions, and the nanoparticles having an increasing number of broken Cd-OOC bonds showed that the trapping centers form the surface were predominant in the photoluminescence emissions. On the other hand, the calculated Huang Rhys factor (S) from both Raman spectra and Stokes shift showed that S increases with decreasing nanoparticles size.