Adjustable Electrochemiluminescence from Highly Passivated CdTe/CdS Nanocrystals by Simple Surface Decoration with Counterions.

Abstract

Tunable optics and electronics of II-VI nanocrystals (NCs) is mainly achieved by using the traditional size-dependent strategy. Herein, we show that the triggering energy (potential), intensity, and even reductive-oxidation electrochemiluminescence (ECL) spectra of highly passivated CdTe/CdS NCs of the same size can be adjusted by simply decorating the NCs with counterions, which proves that surface chemistry can bring about varied electrostatic interactions between the surface vacancies and electrochemically injected carriers for adjustable electrochemical redox induced radiative charge transfer. Potential-resolved ECL demonstrates that increasing the surface sulfur vacancies and decreasing the surface cadmium vacancies can clearly enhance the ECL intensity and lower ECL triggering energy. All the traditional accumulated ECL spectra of CdTe/CdS NCs with various surface vacancies are close to the photoluminescence spectrum of monodisperse NCs without surface treatment, indicating the ECL spectra are mainly dominated by the CdTe core, whereas the slightly redshifted ECL spectrum of CdTe/CdS NCs with excessive cadmium vacancies indicates that the electrostatic repulsion between surface cadmium vacancies and electrons partially consumes the energy of the electrochemically injected electrons. Interestingly, spooling ECL spectra of CdTe/CdS NCs with varied surface vacancies are slightly blueshifted with negatively scanned potential, indicating electrons can be injected into conduction band of higher energy levels in a potential modulated way.