Effect of ligands on the photoluminescence properties of water-soluble PbS quantum dots

In this study, we report the synthesis of PbS quantum dots (QDs) using an aqueous route with three different ligands: thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), l-Cysteine (l-Cys) as the capping molecule. Fourier transform infrared (FT-IR) spectrometry analysis demonstrates that PbS QDs are capped with these three capping ligands through the coordination. The influences of various experimental variables, on the growth rate and luminescent properties of the obtained QDs have been systematically investigated. Experimental results indicate that the capping ligands and pH value plays a crucial role in determining the growth rate and optical properties of obtained PbS QDs. Furthermore, the stability of l-Cys-capped QDs was compared with the TGA and MPA capped QDs were investigated. Experimental results indicate that the l-Cys-capped QDs show better chemical stability than those capped by TGA and MPA. The synthesized l-Cys-capped PbS QDs were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), the results indicate that the QDs were about 8 nm in size and dispersed well with a rock salt crystalline structure.