Microwave-assisted Synthesis Of Semiconductor Nanocrystals: Growth Mechanisms And Its Luminescent Properties

Semiconductor nanocrystals (NCs) have special features such as broad excitation spectra,narrow emission spectra and long fluorescence lifetime. Its potential application insemiconductor-device electronics and biomedical imaging are presented considerableattention in recent years. In comparing with the conventional methods, themicrowave-assisted synthesis, which is known as a green and simple method for theproduction of nano-particles, can enhance the crystallization process and promote the newproduct formation through localized heating at the molecular level. The well-controlledpreparation parameters are considered to relate to the optimal luminescence properties. In thisdissertation, the nanocrystals such as CdSe, CdSe/CdS, PbS and ZnO are synthesized bymicrowave-assisted method. The growth mechanisms and luminescence properties arediscussed. The main results are as follows:1. CdSe and CdSe/CdS core/shell nanocrystals were prepared by microwave-assistedsynthesis method. The growth mechanism was investigated through power X-ray diffraction,Raman spectra, FTIR, UV-Vis and PL spectra. The discussion on rapid preparation ofCdSe/CdS core/shell nanocrystals was owed to the gradual release of sulfur frommercaptonpropionic acid (MPA) under the reaction temperature of140℃. The surface trapstates of CdSe nanocrystals could be effectively decreased by the CdS shell.2. PbS nanocrystals were prepared by microwave-assisted method using inexpensiveand harmless olive oil as a substitute for toxic trioctylphosphine (TOP). A polar solvent suchas glycerol was introduced to serve as heat transferring medium for effective heating. UV-Visand PL spectra have been involved for the discussion of the growth mechanism ofnanocrystals with different precursor molar ratio, reaction temperature and time. The optimalluminescence properties of PbS nanoparticles were achieved at80℃when the precursormolar ratio of PbO:TAA is1:2.3. ZnO nanostructure film was prepared by microwave-assisted method. Theinvestigation for morphology evolution of ZnO nanostructures was performed with SEM,UV-Vis and PL spectra. With the increase of reaction time, the OH-release from HMTintensified the selective etching on (001) planes of the ZnO nanorods, resulting in theappearance of ZnO nanowalls.