Thiolated selenium as a new precursor for the aqueous synthesis of CdSe/CdS core/shell quantum dots

A new hydrothermal method for the synthesis of thiol-protected CdSe/CdS core/shell quantum dots (QDs) starting from thiolated cadmium and selenium is reported. Four different thiols namely; 3-mercaptopropane-1-sulfonic acid (MPSA), 2-mercaptosuccinic acid, 3-mercaptopropanoic acid (MPA) and 2-mercaptoacetic acid were used to prepare the precursors which also served as capping agent and sulphur source. The as-synthesized QDs were characterized by ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy, fourier transform infrared spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. The as-prepared QDs exhibited broad trap emission with longer lifetime (> 100 ns) due to thiolate trap sites. The particle growth kinetics and the photoluminescent quantum yield (PLQY) of the resulting QDs were found to be depended on the type of thiol and pH. The MPA capped QDs synthesized at pH 11.0 exhibited the high PLQY among other thiol capped QDs. The size of the QDs was calculated to be similar to 3 nm by XRD analysis, which is consistent with TEM results. The possible mechanism of the core/shell formation is also presented.