Surface Decides the Photoluminescence of Colloidal CdSe Nanoplatelets Based Core/Shell Heterostructures

The photophysical properties of core/shell semiconductor nanocrystals are influenced by the shell thickness as well by the surface, whether it is cationic or anionic. In this work, we have investigated the effect of thickness of shell as well as the surface terminating layer-anionic and cationic on the optical properties in CdSe/CdS which is a quasi-type-II system and CdSe/ZnS, a type-I heterostructured core/shell nanoplatelets (NPLs). The results reveal that no matter which cation is on the surface - Zn or Cd-the photoluminescence (PL) is always high compared to the surface being anion terminated. An alternating behavior in the PL intensity is observed upon successively terminating the surface with cations and anions, which has been achieved using the colloidal atomic layer deposition (cALD) technique. Not only the PL intensity but also the PL lifetimes and the emission peak widths too follow this similar alternating trend. All of these can be simply explained on the basis of the trap states that are created on the surface depending upon cation or anion termination.