Aqueous Synthesis And Property Of Long Fluorescence Lifetime CdTe And CdTe/CdS QDs

In recent years, tha application fields of quantum dots (QDs) are becoming wider and wider, such as in the biofluorescence imaging. However, the fluorescence lifetime of the QDs is usually only10-40s, which strongly limits their applications. In order to investigate how to prolong the lifetime of QDs, cadmium telluride (CdTe) QDs capped with π-novel ligands were synthesized. The as-prepared QDs exhibited high quantum yield characterized by ultraviolet-visible absorption and fluorescence emission spectra. XRD patterns confirmed the Cubic phase of the obtained QDs and time-resolved fluorescence decay indicated the long fluorescence(PL) lifetime for L1-CdTe of80ns and for L2-CdTe of58ns with550nm as emission wavelength, while the lifetime of QDs obtained via traditional methods hardly exceeding40ns. The practical applications of photosensitive solar cells, photocatalysis and biological monitoring will be promoted based on the prolonged fluorescence lifetime. The effects of several paramount reaction parameters, such as reflux time,reagent concentrations(based on the concentration of Cd2+), pH value on luminescent properties were investigated.Moreover, coating CdTe with CdS to prepare ⅡI-type core-shell QDs is an alternative way to prolong the fluorescence lifetime. In this paper, Ⅱ-type core-shell QDs mentioned above were prepared by two steps in aqueous phase. The effects of reaction time, S/Te molar ratio on fluorescence lifetime were investigated. The results indicated that core-shell QDs with long lifetime and long emission wavelength were obtained via this method easily and reproducibly. The crystalline phase and optical properties were investigated through XRD and absorption,emission spectroscopy, time-resolved spectroscopy respectively. The results revealed the fluorescence lifetimes of L1-CdTe/CdS and L2-CdTe/CdS were significantly prolonged to83ns and75ns respectively.This thesis involved two methods to prolonged the PL lifetime of QDs, which included novel ligands method and CdS shell method. After coated with CdS shell, the life time of L1-CdTe QDs prolonged from65ns to83ns and the quantum yield downed to21%from51%; otherwise, the lifetime of L2-CdTe QDs prolonged from56ns to75ns and the quantum yield downed to19%from43%. However, after capped with ligand, the lifetime of CdTe QDs was prolonged without obvious change of PLQY. Thus, novel ligands method made the QDs have a long lifetime and a high quantum yield.