Photoinduced electron transfer in novel CdSe-Cu2Se type II core-shell quantum dots

Abstract

Herein we report the synthesis, characterisation and electron transfer studies of CdSe-Cu₂Se QDs, a novel type II core-shell system. The synthesis was achieved by a high temperature organometallic method with oleylamine as ligand. Structural and optical properties of the nanostructures were investigated using X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, inductive coupled plasma optical emission spectroscopy, cyclic voltammetry, X-ray photoelectron spectroscopy and absorption spectroscopy. The electron transfer dynamics were investigated by observing the variations in steady state and time resolved emission spectra in the presence of an electron acceptor-methyl viologen. Localization of electrons in the shells was evident from the studies performed indicating efficient charge separation.

Scheme 1. Relative band edges of CdSe and Cu₂Se based on the CV results.

Fig. 1. (a) Normalized UV-Vis absorption and (b) emission spectra of CdSe and CdSe–Cu₂Se core–shell QDs.

Fig. 2. Cyclic voltammograms (CVs) of CdSe–Cu₂Se core–shell QDs.

Fig. 3. HRTEM images of CdSe–Cu₂Se core–shell QDs. Inset shows the SAED pattern.

Fig. 4. EDS spectrum of CdSe–Cu₂Se core–shell QDs.

Fig. 5. X-Ray Diffraction (XRD) patterns of CdSe and the corresponding CdSe–Cu₂Se core–shell QDs.

Fig. 6. High resolution XPS spectra of (a) the core–shell QDs over the entire scan range (b) Cd 3d (c) Se 3d (d) Cu 2p.

Fig. 7. Quenching in the PL intensity of CdSe–Cu₂Se core–shell QDs upon addition of methyl viologen (MV²⁺). (Recorded in hexane and excited at 550 nm.) Inset shows the corresponding absorption spectra.

Fig. 8. Stern–Volmer plots for comparing PL quenching of CdSe (▲) and CdSe–Cu₂Se core–shell (●) QDs in presence of MV²⁺. Inset shows the corresponding TCSPC data (excited at 330 nm), showing little change in average lifetime.