Synthesis and properties of CdSe/ZnS core/shell nanorods

A method for the synthesis of CdSe/ZnS core/shell nanorods is reported. In the first step rods are grown, and in a second step a shell of ZnS is overgrown at moderate temperatures in a mixture of trioctylphosphine-oxide and hexadecylamine. Structural and chemical characterization using transmission electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy were performed providing direct evidence for shell growth. The emission quantum yield significantly increases by over 1 order of magnitude for the core/shell nanorods compared to the original rods because of the improved surface passivation. Rods with lengths up to ∼30 nm were investigated, and in this size regime the maximal achievable QY showed little dependence on length and strong dependence on rod diameter, with increased QY in smaller diameters. Color tunability is available via tuning of the rod diameter. The stability against photooxidation was significantly improved in core/shell nanorods compared with rods coated by organic ligands.