Effects of Core Size and Shell Thickness on Luminescence Dynamics of Wurtzite CdSe/CdS Core/Shell Nanocrystals

Colloidal CdSe nanocrystals (NCs), whose size is 2.8, 3.8, and 4.9 nm, respectively, were successively overcoated with CdS monolayers (MLs). The X-ray diffraction patterns indicated that the stress in the wurtzite CdSe core was increased with the epitaxial growth of CdS shell, and the CdSe lattice contraction, which was sensitive to core size, did not release with the CdS shell toward 5 MLs. The effects of the CdSe core size and the CdS shell thickness on the temperature-dependent photoluminescence (PL) lifetime were investigated. The PL lifetime undulation with temperature is indicative of the spatial distribution of trap states, and the strong interplay between intrinsic excitons and surface traps can be activated even in the case of the NCs with 5 ML CdS shell