Kinetics of the Near Infrared Electrochemiluminescence from Metal Nanoclusters on Surface and in Solution

Abstract

The electronics structures of some metal nanoclusters enable strong photoluminescence in the near infrared spectrum range. Activation of the luminescence via electrode reactions, rather than light source, i.e., electrochemiluminescence (ECL), has received growing interests due to the various potential benefits, but has been mostly limited to steady-state behaviors such as overall emission intensity and materials optimizations. Here, the ECL kinetics in representative experiments where nanoclusters as luminophores are either immobilized on the surface or free diffusing in solution were investigated based on classic theory. An analytical equation derived under a sequential mass transport limit regime quantitates the experimental ECL kinetics features in a wide range of conditions. Deconvolution of non-faradic charging current from redox current provides the threshold in time ranges for the analysis of ECL kinetics. The ECL kinetics profiles suggest that bimolecular or pseudo first order reactions limit the ECL generation immediately following the establishment of the applied potentials, while later ECL generation is governed by diffusion or mass transport displaying a Cottrell type decay over inverse square root time. Physical meanings of key parameters as defined in classic theorem are discussed in representative experimental systems for appropriate quantitation and evaluation of ECLs properties from different materials systems.