Electrochemical Tuning of Localized Surface Plasmon Resonance in Copper Chalcogenide Nanocrystals

Abstract

In this work, we developed a method to study in situ the optical properties of Cu2-xSe and CuS nanocrystals upon electrochemical reduction and oxidation. Both these materials possess a strong localized surface plasmon resonance (LSPR) in the near-infrared region. First, the nanoparticles were embedded into a transparent film made of a perfluorinated sulfonic-acid copolymer Nafion deposited onto an ITO-coated glass. This substrate was employed as a working electrode for chronoamperometry and cyclic voltammetry measurements directly in a transparent cell allowing for simultaneous acquisition of absorption spectra of the system upon its charging/discharging. We observed that LSPR of the Cu2-xSe NCs can be well-controlled and tuned in a wide range simply by potentiostatic potential switching. Starting with an intensive plasmon of the initial as-synthesized Cu2-xSe NCs we were able to completely damp it via reduction (electron injection). Moreover, this electrochemical tuning was demonstrated to be reversible by subsequent oxidation (extracting electrons from the system). At the same time, CuS NCs did not exhibit such prominent LSPR modulation upon the same experimental conditions due to their more metallic-like electronic structure. Hence, our findings demonstrate for the first time a reversible tuning of the LSPR of copper chalcogenide NCs without any chemical or structural modification. Such a wide LSPR tunability is of paramount importance, for example in applications of these materials in photovoltaics to amplify light absorption, in systems involving plasmon-exciton interactions to controllably quench/enhance light emission, and in electrochromic devices to control their transmittance.