Thiol-Ligand-Catalyzed Quenching and Etching in Mixtures of Colloidal Quantum Dots and Silver Nanoparticles

Plasmonic nanostructures have the potential to enhance the emissive properties of semiconductor quantum dots (QDs). Although gold nanoparticles have been widely used for this purpose, other metals, such as silver, are also of interest and have more desirable plasmonic properties; however, silver nanoparticles suffer from chemical instability that gold nanoparticles do not. We find that this instability has the potential to limit the integration of silver nanoparticles (AgNPs) with QDs. Specifically, the common selection of thiol ligands for colloidal stabilization of QDs is incompatible with AgNPs, whether silver nanospheres or silver nanoplates. Equilibrium desorption of thiol ligands from QDs drives a pseudocatalytic process wherein the AgNPs are etched to produce silver(I)-ligand complexes, which then undergo cation exchange reactions at the QD leading to quenching of its photoluminescence (PL) through the introduction of long-lived trap states. We characterize this process through a combination of morphological, chemical, and steady-state and time-resolved spectroscopic measurements. The latter include extinction and absorption, PL emission intensity and lifetime, and transient absorption. Importantly, the etching and quenching process is avoided with QDs that are coated with an amphiphilic polymer instead of thiol ligands.