CdSe/CdS/ZnS and CdSe/ZnSe/ZnS core-shell-shell nanocrystals

We report the synthesis and characterization of highly luminescent colloidal nanocrystals consisting of CdSe cores protected with double inorganic shells (core-shell-shell nanocrystals). The outer ZnS shell provides efficient confinement of electron and hole wave functions inside the nanocrystal as well as high photochemical stability. Introducing the middle shell (CdS or ZnSe) sandwiched between CdSe core and ZnS outer shell allows considerable reducing strain inside nanocrystals because CdS and ZnSe have the lattice parameter intermediate to those of CdSe and ZnS. In contrast to CdSe/ZnS core-shells, in the core-shell-shell nanocrystals ZnS shell grows nearly defect free. Due to high quality of the ZnS shell, the core-shell-shell nanocrystals exhibit PL efficiency and photostability exceeding those of CdSe/ZnS nanocrystals. Preferential growth of the middle CdS shell in one crystallographic direction allows engineering the shape and luminescence polarization of the core-shell-shell nanocrystals.