Depositing ZnS shell around ZnSe core nanocrystals in aqueous media via direct thermal treatment

An aqueous-based route has been demonstrated for the preparation of ZnSe/ZnS core/shell nanocrystals via the directly thermal treatment of the crude ZnSe nanocrystals reaction solution in the presence of additional thiol ligand together with Zn source. The obtained ZnSe/ZnS core/shell nanostructures have tunable and narrow photoluminescence emission from ultraviolet to blue window (370–400 nm). Three common thiol ligands (mercaptopropionic acid (MPA), thioglycolic acid (TGA), and glutathione (GSH)) were tested as the sulfur source for ZnS shell deposition. It was found that with the addition of additional MPA or GSH into the ZnSe crude reaction solution, the PL efficiency of the obtained ZnSe/ZnS core/shell nanostructures can be improved significantly compared with the original ZnSe nanocrystals; while TGA has a quenching effect on the PL efficiency. The effects of experimental variables, including the nature of thiol ligand, amount of thiol ligand, reaction temperature, and pH value, on the synthesis and the optical properties of the obtained core/shell nanocrystals were investigated systematically. In comparison with plain ZnSe cores, both the PL emission efficiency and the stability against chemical oxidation of the ZnSe/ZnS core/shell structures have been improved substantially.