PbSe/CdSe and PbSe/CdSe/ZnSe hierarchical nanocrystals and their photoluminescence.

Multiple CdSe and ZnSe semiconductor shells were grown on PbSe semiconductor spherical cores with monolayer control. For CdSe shell coating, we found that there was little room to further increase the quantum yields of freshly-made high-quality PbSe nanocrystals that already owned very high initial values because of their good surface status; but there was great improvement for the PbSe nanocrystals with low initial quantum yields because of the poor surface status. Nonetheless, the quantum yield for the latter case could not reach the former's value. Additional ZnSe shells on PbSe/CdSe could further increase the quantum yield and protect the nanocrystals from air oxidation. The observed phenomena in the synthesis of the PbSe/CdSe and PbSe/CdSe/ZnSe core/shell structures were explained through the carrier wave function expansion and the surface polarization.