Synthesis Of Novel QDs With High Quantum Yield And Their Photoluminescent Properties

Colloidal semiconductor nanocrystals known as quantum dots (QDs) have been attracted significant attention over the last two decades. Comparing with the traditional organic fluorescent dyes QDs have a series of unique luminescent properties such as narrow emission peak, broad absorption, excellent fluorescent efficiency and strong photostability et al. There is a broad application prospect for QDs in light emitting diode, biolabeling, biological detection and drug delivery. Many kinds of QDs such as core/shell QDs and alloyed QDs have been prepared basing on Ⅱ-Ⅵ group semiconductor QDs. The research of the QDs is still focused on enhancing optical properties, improving their fluorescent properties and photostability as well as strengthening biocompatibility.The QDs with excellent fluorescent efficiency and uniform shape were mainly synthesized by hot-injection method. In this work, we prepared various QDs with highly photoluminescence basing on the hot-injection method, researched the influence of the surface ligands on the fluorescence property and shape of QDs, and groped the experimental conditions of preparing the QDs with higher quantum yield. Moreover, we explored the applacation of QDs in biolabeling.Firstly, we used convenient and efficient approach to synthesize homogeneous alloyed CdSeS with low-cost and low-toxic materials. The influence of the Se/S ratio and reaction time on the photoluminescent properties of CdSeS QDs is investigated systematically through researching the temporal evolution of the absorption and the emission spectrum. The photoluminescent strength of CdSeS reached optimal performance when the molar ration of Cd/Se/S was 3:1:2. Following, the short dendritic CdSeS/ZnS QDs were prepared using the method inspired by the successive ion layer adsorption and reaction procedure, which were composed of CdSeS cores and ZnS branches. Transmission electronic microscopy and X-ray diffraction showed that the CdSeS/ZnS QDs were in a cubic zinc blende crystal structure. The photoluminescent intensity increased significantly when the ZnS branches formed as a result of the charge carriers being confined in the core. The photoluminescence quantum yield of the obtained CdSeS/ZnS core-shell QDs can be up to 90%, which was much higher than that of initial CdSeS QDs (39%). In addition, CdSeS/ZnS QDs had good photoluminescence intensity after they were transferred from organic solvent into aqueous media through ligand replacement using mercaptoacetic acid. Afterwards, the E. Coli 0-157 were not only successfully conjugated with CdSeS/ZnS QDs but also presented clear images under UV irradiation.Secondly, different organic ligands capped CdSe QDs were synthesized with tributylphosphine and oleylamine. The influence of the trioctylphosphine and oleylamine on the shape and photoluminescent properties of CdSe QDs was analyzed when they linked to the surface of QDs alone or together. The linking sites of tributylphosphine and oleylamine was analysized by FT-IR vibrational spectra, and researched the best loading condition of surface ligands. The CdSe/CdZnS core/shell QDs were prepared by coating CdSe with different size using CdZnS. Because of size-dependence, the various color core/shell CdSe/CdZnS were obtained by choosing the size of CdSe and controlling the reaction time, whose photoluminescence peaks covered almost any photoluminescence peaks ranging from 580-615 nM. The core/shell quantum dots are transferred into aqueous solution through ligands exchanging by reduced glutathione and labeled HeLa cells successfully.