Synthesis Control And Characterization Of ZnSe, ZnS And ZnSe/ZnS Quantum Dots

The quantum size effect and the unique optical properties of semiconductor quantum dots (QDs) make them very promising as probe in biomedical application. and light-emiting devices. The II-VI colloidal quantum dots, especially for CdE (E=S, Se, Te), were prepared by colloidal chemistry technique have been investigated popularly due to good monodispersity, uniformity and optical property. Compared with QDs including Cd element, ZnSe and ZnS QDs have the lower toxicity than cadmium QDs, and exhibit tuned photoluminescence colors in the UV-blue range. But the surface of a bare QD is made up of highly active atoms that are not fully coordinated and act like defects unless passivated, which will decrease the quantum yield. To remove these defects and improve the optical property, high quality homogeneous and monodisperse nanocrystals have been passivated with inorganic epitaxial growth.So in this article, by improved metal-organic "Green method", Colloidal ZnSe, ZnS and ZnSe/ZnS core/shell QDs were prepared using cheap and low toxic zinc oxide (ZnO) at an organic solvent system of 1-hexadecylamine (HDA), lauric acid (LA) and tri-n-octylphosphine (TOP). The effects of component ratio, reaction temperature and growth time on quantum dots size, UV-Vis absorption and fluorescence properties of ZnSe, ZnS QDs were mainly researched. The results showed that ZnSe and ZnS quantum dots possessed the wurtzite structure, and provided with good uniformity, dispersity and fluorescent characteristics. The influence of the component ratio, the reaction temperature and the growth time on the growth process and the properties of the resultant ZnSe QDs were remarkable. Choosing the optimal parameters, ZnO:HDA:LA = 1:2.1:5.2, TOPSe = 1mol/L, ZnSe QDs obtained the largest range of the size evolution under the condition of nucleation at 280℃and growth at 240℃. With the growth time increasing, the diameter became larger and the emission peak had obvious red shift.ZnSe/ZnS core/shell QDs were synthesized by conventional two-step overcoat growth method based on the preparation of bare ZnSe QDs. The fluorescence intensity of ZnSe/ZnS core/shell QDs had been improved evidently compared to bare ZnSe QDs, and the ZnSe/ZnS core/shell QDs also had the good uniformity and monodispersity.