Effect of Shell Thickness on the Optical Properties in CdSe/CdS/Zn0.5Cd0.5S/ZnS and CdSe/CdS/ZnxCd1-xS/ZnS Core/Multishell Nanocrystals

The evolution of optical properties of two types of core/multishell nanocrystals (NCs)-type A (CdSe/CdS/Zn0.5Cd0.5S/ZnS) and type B (CdSe/CdS/ZnxCd1-xS/ZnS)-with an increase of shell thickness from 3.5 to 15.5 monolayers (MLs) has been studied. When the shell thickness was 9.5 MLs and more, the stability would be greatly improved and the quantum yields (QYs) almost did not change during the process of purification. Even after phase transfer experiment, the QYs of the water-soluble NCs were still kept 70-99% of their initial level. The as-prepared water-soluble NCs with 9.5 MLs and more also exhibited high stability in varying physiological conditions under PBS buffer and continuous UV radiation. For type B core/multishell NCs, due to a consecutive change of lattice parameters from core to shells, there were almost no defects induced between the CdSe core and ZnS shell. As a result, they had higher QYs and stability than type A core/multishell NCs at the same test condition.