Role of Redox Reaction and Electrostatics in Transition-Metal Impurity-Promoted Photoluminescence Evolution of Water-Soluble ZnSe Nanocrystals

Abstract

In this article, the experimental variable-dependent photoluminescence (PL) evolution of transition-metal-doped ZnSe nanocrystals (NCs) is analyzed by combining the redox reaction and the electrostatics of aqueous NCs. Bulk doping of NCs involves two steps − surface adsorption of the metal impurities and the followed internal doping. The former relates to the electrostatics of aqueous NCs, whereas the latter relates to a redox reaction between the impurities and mercapto-ligands. Both of them occur on the NC surface. In this context, aqueous NCs are essentially charge-stabilized particles. The electrostatic factors that weaken the electrostatic repulsion will facilitate the adsorption of metal impurities on NC surfaces, thus benefiting the surface redox reaction. It furthermore promotes the internal doping of the metal impurities. Consequently, the trap emission and the PL evolution of NCs are facilitated. Besides, the internal doping is favored for the metal impurities with high reduction potential because they are easily reduced by mercapto-ligands. Furthermore, because the presence of metal impurities in NC solution both promotes the oxidation of mercapto-ligands and weakens the interparticle electrostatic repulsion, the colloidal solution of doped aqueous NCs is theoretically proved unstable.