A simple and economical one-pot method to synthesize high-quality water soluble CdTe QDs

Abstract

A simple and economical one-pot method to synthesize high-quality water soluble CdTe QDs is reported. An 83% quantum yield (QY) was reached using TGA as the ligand in aqueous solution without protection of nitrogen gas when using K₂TeO₃ as a stable Te source and NaBH₄ as reducing agent. The size of the CdTe NCs could be tuned by the duration of reflux and easily monitored by absorption and PL spectra. At the optimum conditions (pH = 10.5, the concentration of Cd²⁺ was 1.0 mmol l⁻¹ and the ratio of Cd²⁺ : Te²⁻ : TGA : NaBH₄ was 1 : 0.2 : 1 : 10), the maximal QY reached 83%, which was much higher than that of samples prepared by the traditional refluxing aqueous solution method. 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 PL QY and stability of the CdTe QDs. The temporal evolution of the absorption spectrum of thioglycolic acid indicated that TGA was decomposed and released S²⁻ during the preparation of CdTe QDs. The S²⁻ reacted with Cd²⁺ to form CdS, this is consistent with the XRD results. 3-Mercaptopropionic acid (MPA) was also used as a ligand in this system and the results indicate that high quality multi colour CdTe NCs could also be obtained using MPA as the ligand. By this simple method, there is no need of N₂ protection, buffering solution, special ligands, large quantity of N₂H₄ or particular treatment (such as microwave, or ultrasonication).