Synthesis And Properties Of CdS And CdSe Quantum Dots In Two Liquid Phase System

Quantum dots(QDs), named semiconductor nanocrystals, have been widely applied to biomedicine, laser, solar cell and so on, due to their unique optical and electronic properties. The synthesis of QDs with high quality by a facile, green and controllable approach has attracted the increasing interests of numerous research groups.In this article, the synthesis of CdS and CdSe QDs in two liquid phase system was studied. The influence on the structures and properties of QDs were discussed in the views of thermodynamics and dynamics. The two liquid phase system promoted the development of the synthetic chemistry of QDs and built a foundation for the applications of QDs in the fields of biological detection and opticals.The CdS QDs were synthesized at the 1-octadecene(ODE)/glycerol interfaces via a one-pot approach. In this approach, all chemicals were loaded in one pot together.Compared with the common two-phase process, the one-pot route was proved to be a feasibility method. By the adjustion of reaction time, reaction temperature and the molar ratio of Cd/S, the size distribution of CdS QDs was in the range of 2.3~5.0 nm, and the minimum FWHM(full width at half maximum) was only about 23 nm., As-synthesized CdS QDs, with high molar ratio and reaction temperature, showed the narrow size distribution and the good surface structure of crystal. The increasing of Cd/S molar ratio led to the smaller size of CdS QDs, and the increasing of reaction temperature made the bigger one.The amine-capped CdSe QDs were prepared in a 1-octadecene(ODE)/water two liquid phase system at 100 o C via the two-step route. The Cd-precursor was prepared by the reaction of cadmium acetate and dodecylamine(DDA). And the Se-precursor was prepared by the reduction of selenium with sodium borohydride. The sizes, morphologies,and optical properties of CdSe QDs were characterized by electron transmission microscope(TEM), Fourier transform infrared spectrometer(FT–IR), fluorescence spectroscopy(PL) and ultraviolet visible absorption spectroscopy(UV–vis), respectively.The influences of reaction time, reaction temperature and molar ratio of Cd/Se on the size,size distribution, structure and performance of CdSe QDs were discussed. The results showed that the different sizes of CdSe QDs would be prepared in the range of 70~100 o C and molar ratio of Cd/Se in 2:1~8:1. In addition, as-synthesized CdSe QDs had the high stability.In the ODE/water two liquid phase system, the amine-capped CdSe QDs, in which the reductant was hydrazine hydrate and the ligand was dodecylamine(DDA), were prepared via the two-step route. The reaction temperature, Cd/Se molar ratio and concentration of DDA influented the surface states of amine-capeed CdSe QDs. The“Magic-sized” CdSe nanoclusters, in which the reductant was hydrazine hydrate and the ligand was oleic acid(OA), were prepared. Meanwhile, the influence of p H on the structure and stability of CdSe nanoclusters was discussed. The results indicated that the CdSe nanoclusters were stable in different pH.