Synthesis Of CdSe/ZnS QDs In Ethanol And Their Optical Behaviors

Nanometer semiconductor quantum dots (QDs), because of their unique quantum size effect and the quantum confined effect as well as excellent fluorescence properties, can be used in solar cells, marking biological molecules or cells, ion detection and so on. The QDs synthesized by aqueous phase are easy to use with low cost and less toxicity. However, as compared to those synthesized from organic phase, the fluorescent performance of the QDs from aqueous phase is rather poor. As inspired by the fact that water is small molecule, we synthesized CdSe QDs in ethanol. Then we tried synthesis of CdSe/ZnS QDs in ethanol and investigated the optical behaviors of the QDs.First of all, the CdSe QDs were synthesized from water and ethanol. Their optical properties were assessed via ultraviolet-visible (UV-Vis) absorption spectrum and fluorescence spectrum. We compared their optical performances to clearify the effect of solvent. The results show that the CdSe QDs from ethanol have super PL eimission with high brightness. Ligands have an important influence on the optical properties of QDs. So we used two kinds of ligands (TGA and MPA) to synthesize CdSe QDs. The results show that when TGA is used as ligand, the obtained CdSe QDs have better fluorescence performance.Secondly, the core-shell structure of QDs can reduce the surface defects, leading to better optical performance and stability. In order to further improve the fluorescence performance of the CdSe QDs, we synthesized core-shell CdSe/ZnS QDs in ethanol by cladding the CdSe QDs with a ZnS shell. In order to find an appropriate method to synthesize the core-shell CdSe/ZnS QDs, the CdSe QDs were cladded in water and in ethanol for comparision. The ultraviolet-visible absorption spectrum and fluorescence spectrum was used to characterize their optical properties. The results show that by cladding the CdSe QDs in ethanol, the optical performance and stability of the CdSe/ZnS QDs have better fluorescence performance.Finally, we studied the core-shell CdSe/ZnS QDs synthesized under different temperature with different amount of ZnS. Then we used ultraviolet-visible absorption spectrum and fluorescence spectrum to characterize their optical properties. The results show that as the reaction temperature increases from 30℃ to 70℃, the core-shell CdSe/ZnS QDs grow faster and the optical properties of the QDs are better. When the Cd/Zn was 1/6, the fluorescence properties of the core-shell CdSe/ZnS QDs are the best.