Ion-Mediated Photoluminescence Enhancement in CuInS2 Quantum Dots and Its Use as Heavy Metal Ion Sensor

Abstract

The absence of heavy metal ions and excellent photoluminescent (PL) properties make CuInS2 quantum dots (QDs) ideal candidates for a wide range of PL applications. One of these applications stems from their inherent capacity to respond to the presence of Cd2+ ions, which significantly enhances their photoluminescence emission. This property enables the creation of Cd2+ sensors based on the detection of variations in the PL emission or PL lifetime. Aiming to understand the enhancement effect that the presence of Cd2+ exerts on these CuInS2 QDs, we synthesized and characterized a set of CuInS2 QDs covered with varying ZnS shell thicknesses, which were used as Cd2+ probes. The analysis of PL features demonstrated that the presence of Cd2+ ions blocks surface traps on the CuInS2 QDs, minimizing nonradiative decay pathways and therefore increasing both the PL lifetimes and the PL emission of the QDs. In contrast, the incorporation of a ZnS shell passivates the surface of the QDs, reduces the number of accessible surface traps, and diminishes the sensitivity toward the Cd2+ ions. This knowledge has been used to create a sensor that can be used to selectively detect the presence of Cd2+ in the micromolar range, which can even be seen with the naked eye, and exhibits a linear range from 0.05 to 10 μM