Synthesis And Properties Of Water Soluble CdTe And CdTe/CdSe QDs

In recent years, quantum dots (QDs) have attracted much attention due to their excellent opto-electric properties. In this paper, a simple and economical one-pot method to synthesize high-quality water soluble CdTe QDs was investigated.83%quantum yield (QY) was reached using traditional ligand TGA in aqueous solution without protection of nitrogen gas when using K2TeO3as stable Te source and NaBH4as reducing agent, which was much higher than traditional refluxing aqueous solution method. The size of the CdTe NCs could be controlled by the duration of reflux and easily monitored by absorption and photoluminescence (PL) spectra. The X-ray diffraction (XRD) patterns indicated that CdS was formed in the preparation process of CdTe NCs. This CdS shell could effectively passivate the surface trap states, and enhance the PLQY and stability of CdTe QDs.3-mercaptopropionic acid (MPA) was also used as ligand in this system and the results indicate that high quality multi-colour CdTe NCs can also be obtained using MPA as ligand. By the simple method, no N2protection, buffering solution, special ligands and particular treatment (such as microwave, and ultrasonication) were required. The reaction parameters play an important role in the property of CdTe NCs. We also discussed the methods to control the optical property of CdTe NCs by different reaction conditions, such as pH value, concentration of Cd2+, TGA/Cd, Cd/Te and the type of ligand in this paper.Because of its long fluorescence emission wavelength and high PLQY, CdTe/CdSe core/shell QDs has been researched widely these years. CdTe/CdSe core/shell QDs were synthesized in aqueous media without protection of N2by sequentially adding freshly prepared mixture of Na2Se03and NaHB4, Cd(CH3COO)2·H2O and TGA to a solution of CdTe QDs prepared in aqueous solution. In this method, CdTe/CdSe core/shell QDs is very stable in aqueous solution and the PLQY was high (up to73%). The effect of shell layers on the absorption and emission properties of the resulting QDs were investigated. As the number of CdSe layers was increased, the absorption and fluorescence emission spectra of the CdTe/CdSe core/shell QDs extended to longer wavelengths, and the quantum yield increased first and then decreased. The diffraction peaks of the CdTe/CdSe QDs shifted from the standard positions of CdTe diffraction peaks to those of CdSe due to the CdSe layers. And this indicates that the thickness of the CdSe shell increases gradually.