Studies On Synthesis And Luminescence Properties Of Cdse Quantum Dots

Quantum dots (QDs) are semiconductor nanocrystalline,which are a novel class of inorganic fluorophores, and widely studied because of high fluorescence efficiency and quantum size effect. Recently, the research of the semiconductor CdSe QDs is growing vigorously, which gains widespread use due to its exceptional luminescence properties, so CdSe QDs play an important role in many fields. CdSe QDs are synthetized without oxygen in organic phase with high temperature, it is easy to get monodispersed, scale-controlled, high luminescent nanocrystal under those conditions. However,the synthesized QDs in the nonpolar organic phase are insoluble in the polar solvents, which restricts the applications of the QDs in the biological detection, biosensor and bioengineering. Recently, various methods of surface modification of CdSe QDs have been tried in order to make QDs to get wider use. This paper mainly includes three aspects in the following to improve the luminescence property of CdSe QDs in polar solvents.(1) In this work, CdSe QDs were synthesized by the classical method. Photoluminescence (PL), UV-Vis, and transmission electron microscopy (TEM) are used to characterize the synthesized CdSe QDs, and the results show that particle size is about 3.5 nm at diameter with good monodispersity, high fluorescence efficiency, and the first exciton absorption peak at approximately 570 nm. These are consistent with the results reported in the literatures. There are many factors to influence CdSe QDs quality. It is possible that selecting octadecylamine (ODA) as a capped reagent and making selenium and cadmium ratio for 10 : 1 can make QDs with high quality.(2) CdSe QDs are first transferred from the nonpolar organic solvents to the polar solvents by replacing ODA with polyvinylpyrrolidone (PVP) to prepare CdSe/PVP QDs,but the fluorescence quantum yields (QY) of CdSe/PVP QDs considerably reduce in these polar solvents, which indicates that solvent properties can effect greatly on the fluorescence of QDs. The researches find the luminescence properties of CdSe/PVP QDs are improved after UV radiation. Particularly, QY of QDs in the methanol is increased significantly. Many methods are used to explain the mechanism of fluorescence intensity of QDs.(3) CdSe/PVP QDs with di-tert-butyl peroxide (DTBP) in the methanol have more QY than QDs without DTBP after UV radiation. The researches show the concentration of DTBP influences on the luminescence of QDs. When the ratio of DTBP and CdSe QDs is less than 100, QY of QDs has no obvious change because of weak oxidation ability of DTBP. Along with increasing DTBP, the luminescence intensity of QDs is increased dramatically. When the ratio of CdSe and DTBP reaches 1 : 300, QDs exhibit maximal luminescence intensity. It is clear that 1 : 300 is the best ratio CdSe and DTBP.