Study On The Synthesis And The Properties Of Semiconductor Quantum Dots Via Poly-phase System

Semiconductor nanocrystals, also called quantum dots (QDs), show quantum size effects which distinct from these of the corresponding bulk materials, that have been widely applied in the photo catalysis, optical absorption, photo-electric conversion, bioluminescence labeling and so on. Among these semiconductor materials, groupâ…¡-â…¥semiconductor nanoparticles, especially CdS and CdSe nanoparticles, have been extensively studied due to the ability to tune their emission in the visible range simply by changing their size, and due to the advances in their preparation.Based on the former research experiences, we firstly give out a three-phase reaction mechanism. And we have prepared CdS, CdSe QDs and CdS/ZnS, CdSe/CdS, CdSe/ZnS core-shell QDs via this three-phase system. The sizes and the shapes of as-synthesized QDs were characterized by XRD, TEM techniques. UV-Vis absorption and PL spectroscopy were used to characterize the optical properties of QDs. As a result, the QDs are cubic crystal structure, narrow sized distribution and uniform morphology, and the properties of PL spectroscopy were characterized by UV-Vis absorption spectra and photoluminescence spectra.The high surface defects of the single nanocrystals may lead to the reduced luminescence efficiency and photochemical degradation. Band gap engineering concepts borrowed from materials science and electronics have lead to the development of core-shell nanocrystals sample with high room temperature quantum yields and much improved photochemical stability. By enclosing a core nanocrystal of one material with a shell of another having a large band-gap, one can efficiently confine the excitation to the core, eliminating nonradiative relaxation pathways and preventing photochemical degradation. Herein, we get the same conclusion as above mentioned from our experiment, Which is the exciton emission of core QDs was greatly improved by covering with a proper layer of shell. In summary, the synthesized core-shell monodispersed QDs with high quantum yield and narrow PL spectra have been widely applied in the biotechnology as bioluminescence labeling. We know that is very important to the life research.