巯基包覆CdSe和CdSe/CdS核壳纳米晶的水相合成与表征

利用水相合成的方法制备了巯基包覆的具有较高荧光量子产率的CdSe和CdSe／CdS纳米晶．水相合成方法的优点是原料低廉、安全可靠和重复性高，缺点是纳米晶的尺寸分布较宽，发光效率不是很高．采用X-射线粉末衍射、吸收和荧光等光谱手段对纳米晶的平均尺度、粒径分布、晶体结构及发光特性进行了表征。在77K到300K的温度范围内，随着温度降低，CdSe纳米晶的发光峰逐渐蓝移，而CdSe／Cds纳米晶发光峰位基本不随温度变化而变化．此外，在325nm激光辐照下，CdSe／CdS纳米晶的荧光寿命比CdSe纳米晶延长了6倍左右，稳定性大幅度提高．以上结果表明，核壳结构的CdSe／CdS纳米晶具有较高的发光效率和良好的稳定性，具有广阔的应用前景．

Synthesis and Characterization of Thiol-Capped CdSe and CdSe/CdS Core/Shell Nanocrystalsin Aqueous Solution

Thiol-capped CdSe/CdS core/shell nanocrystals(NCs)which show high luminescence quantum yield are synthesized in aqueous solution.The synthesis in an aqueous medium without any poisonous materials is attached importance to.The simplicity and high reproducibility are notable among the advantages of the aqueous synthesis.A combination of X-ray diffraction(XRD),UV-Vis absorption spectroscopy and photoluminescence(PL) spectroscopy are employed to analyze the NCs and determine their crystal structures,optical characters and stabilities.Furthermore,PL properties are studied in a temperature range between 77 K and 300 K,which haven't been reported before. The PL peak position of CdSe NCs shifts toward shorter wavelengths and the band becomes sharper with decreasing temperature.At the same condition, the PL peak position of CdSe/CdS NCs keeps unconverted nearly with the variation of temperature. The results indicate that the CdS shell can improve the temperature-dependent stability of CdSe NCs effectively.Photostabilities of CdSe and CdSe/CdS NCs are compared under 325 nm laser irradiation.It takes 78 s that the PL intensity decrease to the half for CdSe NCs,but 442 s for CdSe/CdS core/shell NCs.The fluorescence lifetime increases about six times due to overcoating.The CdSe/CdS NCs will be useful in the practical application for their advantages in synthesis procedure and optical properties.