Microwave-assisted Synthesis And Properties Of Water-soluble Doped ZnS Nanocrystals

Nanotechnology is the operation and control for the atom or molecule in the nanometer scale to discover the new properties of materials and develop their functions. Development and application of nanopmaterials is most important for nanotechnology. It is expected that the photoelectric and magnet properties of nanomaterials will be improved by the precise control for the synthesis, composite and assemble of materials and applied to the conventional industries to reconstruct these industries for the benefit of humanIn the field of nanotechnology, nanoparticles have been extensively investigated due to their unique properties compared with the corresponding bulk materials. These properties result mainly from quantum confine effects and surface effects. These new properties will lead to new, high-performance products and technologies that were not possible before.At present, bio-nanotechnology has been the focus of research field. Since the size of most important biomolecules, such as protein of DNA etc., are similar to the nanoparticles (0.1nm-100nm), so the utilization of nanoparticles as biotechnological tool are particularly attractive. One of such application is usingfluorescent semiconductor nanocrystals as labels for biological tagging experiments, because they have more advantage as labels compared to existing organic dyes, such as wider excitation, narrower emission, higher stability and lower background. This has led to rapid commercialization of the new nanotechnology. For this reason, the development of a successful synthetic scheme of high quality nanocrystals is very important. My dissertation works aim to develop a versatile synthetic method of doped nanocrystals with high fluorescencent efficiency on the base of the previous work and investigate the luminescent properties of nanocrystals obtained.1 water soluble ZnS nanocrystals were synthesized by decomposition of Zn-MPA complex under microwave irradiation. The ratio of Zn ion and MPA molecule is the important effect factor for formation of ZnS nanocrystals during microwave treatment. Only when the ratio of MPA molecule and Zn ion is more than 2.5, ZnS nanocrystals could be synthesized. When the ratio is less than 2.5, formation of nanocrystals will depend on the PH value of the Zn-MPA complex solution. In weak base range, ZnS nanocrystals can be obtained, and ZnO nanocrystals can be synthesized in strong base range. We suggest that the amount of hydroxy group in the solution can effect the stability of Zn-MPA complex with this ratio of Zn ion and MPA.2. We synthesized water-soluble Mn doped ZnS nanocrystals with MPA (3-mercaptopropionic acid) as stabilizer. On the base of ZnS nanocrystals formed from decomposition of Zn-MPA complex, ZnS:Mn/ZnS core-shell nanocrystals were synthesized by combination of ZnS:Mn nanocrystals and Zn-MPA complex under microwave irradiation. The obtained core-shell nanocrystals have higher fluorescence efficiency and photostability. Fluorescence decay and ESR measurements were employed to confirm thathigher quantum yield of nanocrsals is due to the improvement of the isolated Mn ions distribution in ZnS lattice. While higher stability of nanocrystals could result from the formation of the compact ZnS shell.3. ZnS:Cu nanocrystals with tunable emission were synthesized by microwaveirradiation method, especially ZnS:Cu nanocrystals with yellow emission were prepared, which has been never reported whether in bulk ZnS:Cu or in nanocrystals ZnS:Cu. Fluorescence decay, fluorescence at various temperature, surface photovoltage transient and XPS measurements were employed to invesitage the methnisiom of different color emission for obtained ZnS:Cu nanocrystals4. Water-soluble Ag doped ZnS nanocrystals with MPA (3-mercaptopropionic acid) as stabilizer were synthesized. On the base of ZnS nanocrystals formed from decomposition of Zn-MPA complex, ZnS:Ag/ZnS core-shell nanocrystals were synthesized by combination of ZnS:Ag nanocrystals and Zn-MPA complex under microwave irradiation. The obtained core-shell nanocrystals have higher fluorescence efficiency (more than 10%) and photostability. Due to the photoelectric conduction property of ZnS:Ag nanocrystals, surface photovoltage transient measurement were employed to confirm that higher quantum yield of nanocrsals is due to the improvement of the isolated Ag ions distribution in ZnS lattice. While higher stability of nanocrystals could result from the formation of the compact ZnS shell.