Structure-optical property correlation in CdTe/CdS core-shell quantum dots and their effects on Cu2+ sensing mechanisms

ABSTRACT A rapid and simple aqueous method has been developed for synthesizing CdTe/CdS core shell quantum dots (QDs) by refluxing glutathione (GSH) with Cd2+ and Te2- precursors at 100 °C without using inert medium. Here GSH has dual role, i.e., as an in-situ source of sulphide for deposition of CdS on CdTe and as a capping agent to stabilize the CdTe/CdS QDs. As the refluxing time was enhanced from 15 min to 105 min, the sizes of the spherical shaped CdTe/CdS QDs increased from 2.8 ± 0.8 nm to 3.9 ± 1.1 nm, the crystalline nature improved, GSH capping content decreased and the CdS shell deposition was increased. The size dependent change in photoluminescence (PL) from green to red was observed. The photoluminescence quantum yield (PLQY) was improved with refluxing time and its maximum value was obtained for the batch synthesized by 60 min refluxing. The PL of these QDs were drastically quenched by ppb levels of Cu2+ ions, the relation between structural changes in the QDs and Cu2+ ion detection mechanism has been studied. Instead of the batch with maximum PLQY, the best Cu2+ sensitivity and selectivity against several metal ions were obtained for the batch synthesized by refluxing for 30 min owing to optimum GSH capping. The optimal capping network and the thiol groups guided Cu2+ ions close to the surface of the CdTe/CdS QDs for electron transfer phenomenon to occur. The delocalization of photoexcited electrons from CdTe core to the CdS shell and its further transport to the Cu2+ ions in the surrounding medium favoured electron transport mechanism, as supported by enhanced rate of non-radiative decay in the PL decay kinetics study.