Electron transfer in a bandgap and composition engineered CdS/ZnS/ZnSe core/shell/shell nanocrystal: Synthesis and characterization.

by Qi, Hang; Rutherford, Michael; Peng, Xiaogang

By inserting a wide bandgap ZnS barrier layer into CdS/ZnSe core/shell nanocrystal whose bandgap offset is type-II in nature, studying electron transfer in a single colloidal nanocrystal is made practical. In such a CdS/ZnS/ZnSe core/shell/shell nanocrystal with fix CdS core diam. and ZnSe shell thickness, the efficiency of electron transfer from ZnSe outer shell to CdS core is affected by the ZnS barrier layer thickness and indicated by the quantum yield (QY) of indirect type-II photoluminescence emission. The type-II emission intensity decreases with the increase of ZnS barrier layer thickness while the bandgap emission from CdS core and ZnSe outer shell increases at the same time. By tuning the thickness of ZnS barrier layer, CdS/ZnS/ZnSe nanocrystals can show single emission (type-II), dual emissions (bandgap emission of CdS core and ZnSe outer shell) and three emissions (all of above). A brief quant. anal. of QYs of there three emissions are also shown here.