Tuning The Trap Emission And The Impurity Emission Of Aqueous ZnSe Quantum Dots

This thesis focuses on the preparation, optical property tuning and luminescent mechanism for aqueous ZnSe quantum dots (QDs). We have investigated the influence of several experimental conditions during the synthesis of QDs, including precursor injection manners, nucleation temperatures, solution pH values, and ligand feeding ratios. By rationally combining these experimental conditions, many types of ZnSe QDs, such as MnSe:ZnSe, Cu:ZnSe and Mn:ZnSe/Cu:ZnS QDs, with anticipative fluorescence can been synthesized. This work is expected available to investigate the growth mechanism of high performance ZnSe QDs. The main results are shown below:A novel cation-inverting-injection method was developed to synthesize aqueous ZnSe QDs with improved luminescent properties. This method can effectively suppress the consumption of monomers during QDs nucleation stage by reducing the reactivity of monomers and providing a high nucleation temperature, leaving more monomers retained in QDs’ growth stage. As a result, big size ZnSe QDs with good surface modification, suppressed trap luminance, and strong blue band-gap luminance can be obtained. The photoluminescence (PL) quantum yield (QY) of QDs reaches a new record of 15%.The influence of nucleation temperature on the optical property of MnSe:ZnSe QDs was investigated in detail. MnSe nuclei synthesized under different nucleation temperatures show distinct core size, core concentration, present state, and trap cmission. By simply adjusting the nucleation temperature, the emission color of QDs can be precisely encoded according to the PL intensity ratio between the trap emission and Mn2+-induced emission. This work makes a contribution to preparing multiple fluorescent single QD codes at nanoscale range.The detailed mechanism for tuning the emission of MnSe:ZnSe QDs was investigated. By controlling the experimental conditions, like solution pH, ligand feeding ratio, and monomer injection manner, single colored MnSe:ZnSe QDs or multicolored MnSe:ZnSe QDs with double or triple emission peaks can be successfully prepared. The distribution and emission intensity of the interface defects between MnSe core and ZnSe shell are believed as the key for tuning the emission of MnSe:ZnSe QDs.The emission of aqueous Cu:ZnSe QDs was explored to the yellow light range. Our results show that high solution pH, multiple injections of Zn precursors, and nucleation doping strategy could contribute to the form of Cu:ZnSe QDs with big size and low conduction band energy. As a result, the emission window of as-prepared Cu:ZnSe QDs can be extended to yellow light window.White emitted aqueous Mn:ZnSe/Cu:ZnS QDs were prepared via co-doping strategy. By doping Mn2+ in the core and Cu2+ in the shell, the co-doped QDs present three emission bands:Mn2+-induced emission, trap emission of ZnSe, and Cu2+-induced emission. The overall results for these three types of emission lead to white emission in Mn:ZnSe/Cu:ZnS QDs. This work not only offers method for manipulation of optical properties of ZnSe QDs, but also provides white light materials light emitting diodes (LED).