Optimize Synthesis Of CdX Semiconductor Nanomaterials In Water Phase

Semiconductor nanoparticles (QDs), or quantum dots,are generally composed of atoms from elements of groups II–VI orâ…¢-â…¤in the periodic table. At present, much studies are concerning YX(Y=Cd,Zn;X=S,Se,Te).Because of their variety of size-and shape-dependent optical and electrical properties, quantum dots have been attracting extensive attention for practical applications, such as biological labels, photovoltaic devices, and lasers. At the present time, two general approaches have been reported for the synthesis of QDs. One is the organometallic route. The as-prepared QDs are generally capped with hydrophobic ligands, so that they cannot be used in reality directly. The other is the aqueous synthesis route, that produce QDs in water phase. In this way, the as-prepared QDs own biological compatibility, and stability.CdTe is an important semiconductor material. CdTe QDs show increasing promise due to their large exciton Bohr radius (7.3 nm) and narrowbulk band gap of 1.475 eV. CdTe QDs have been widely studied as luminescence probes and sensors. This dissertation has studied synthesis of CdTe quantum dots and the core-shell CdTe/CdS quantum dots in water phase。The samples are characterized through photoluminescence spectra (PL), transmission electron microscopy (TEM), atomic force microscope (AFM) and X-ray powder diffraction (XRD). The results and conclusions acquired from the dissertation are as follows: (1) The CdTe semiconductor quantum dots are synthesized in water with 3–Mercaptopropionic Acid (MPA) as stabilizer. The results show that temporal evolution, temperature, pH, the molar ratio of Te2- and Cd²⁺ , the molar ratio of MPA and Cd²⁺ have a great effect on the particle size of CdTe quantum dots, size distribution and the rate of growth. This experiment studied these influencing factors systematically. (2) Different shell thickness of semiconductor CdTe/CdS core-shell quantum dots were synthesized in water phase. Experimental results show that: the reaction time, temperature, concentration of Na₂S and the amount of NaOH have great influence on the shell thickness of the CdTe/CdS quantum dots and the intensity of the fluorescence. This experiment's advantages are mild conditions, operated simply, inexpensive reagents and suitable for promotion.