New strategy for band-gap tuning in semiconductor nanocrystals

In the last decade, the main efforts have focused on the preparation of different sized binary II–VI group semiconductor nanocrystals to obtain different color-emitting luminescence. However, the tuning of physical and chemical properties by changing the particle size could cause problems in many applications, in particular if unstable small particles are used. Recent advances have led to the exploration of tunable optical properties by changing their constituent stoichiometries in ternary alloy nanocrystals. High-quality Zn _x Cd_1?x Se alloy nanocrystals have been successfully prepared at high temperature by incorporating stoichiometric amounts of Zn and Se into pre-prepared CdSe nanocrystals or embryonic CdSe nuclei. With increasing Zn content, a composition-tunable emission across the whole visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength. High-quality alloy Zn _x Cd_1?x S nanocrystals have been obtained by the conucleation and co-growth of the constituents through the reaction of a mixture of CdO- and ZnO-oleic acid complexes with sulfur at elevated temperatures. The obtained Zn _x Cd_1?x S alloy nanocrystals possess superior optical properties with photoluminescence quantum yields of 25–50%, especially the extremely narrow emission spectral width (fwhm=14 nm).