| In variety of nano-sized materials, more and more attention was paid to CdS quantum dots (QDs) because of their excellent optoelectronic properties and it potential in application. Nanoparticles show significant quantum-size effect (such as energy band discreteness, band gap broadening, blue shift in spectra etc.) as sizes of particles are smaller than Bohr radis of exciton of bulk material with same composition (for example, CdS's Bohr radium is 6nm). There have been a variety of ways to be introduced into the synthesis of quantum dots of sulfides, this thesis focus on the synthesis of CdS QDs with principles of organic molecule stabling (or surface modification), size selective precipitation. The characterization on those nano sulfide QDs are also presented in the thesis. As nanoparticles with core shell structure have much higher fluorescence quantum efficiency, base on CdS of synthesis, some efforts have also been put into the experiment on synthesis of CdS/ZnS core-shell particles.Some interesting conclusions from this work are listed as follows:1. The detailed description on synthesis of CdS QDs have been given in the thesis, included the ideas such as aqueous solution synthesis, control of nucleation process, surface modification with small mercapto organic molecule, size selected precipitation etc.. CdS QDs dispersible in aqueous solution with long stability have been realized.2. A series of nanoparticles with different size can be obtained from just one reaction process based on the technology of time control and sampling in different phases as suggested by Ostwald ripening theory in colloid chemistry.3. As the fact that nanoparticles from orginal reaction solution have much wider size distribution with deviationσlarger than 15%. Size-selective precipitation was applied to sharpen the size distribution of those nanoparticles. A size series of QDs with improved monodispersity can be achieved just from one sampling solution. |
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