Near-Infrared Emitting Type-II CdTe/CdSe Core/Shell Nanocrystals: Synthesis and Optical Properties

Type-II CdTe/CdSe core/shell (C/S) nanocrystals (NCs) have been synthesized with 1-octadecane (ODE) by chemical methods. The formation of type-II C/S structures were clarified by spectro-metric techniques of UV–vis absorption, photoluminescence (PL) and Raman scattering (RS). Observation results from X-ray diffraction (XRD) reveal that both CdTe core and type-II CdTe/CdSe C/S NCs crystallize in the cubic phase with zinc-blende structure. By changing CdSe shell thicknesses from 1 to 4ML, the PL peaks of CdTe/CdSe C/S NCs could be adjusted from 801 nm to 871 nm (in near-infrared), respectively. These results prove that the partial separation of photoexcited carriers is dependent strongly on the shell thicknesses. As increasing the excitation power, the PL peaks of CdTe/CdSe NCs move towards high energy and increase with a third root of the excitation power. These observations have been explained by the band bending (BB) effect, which is resulting from the spatially separated photoexcited carriers in type-II C/S NCs.