Electrochemical control of photoluminescence in pure wurtzite CdSe/CdS core/shell nanocrystals

Abstract

Spectroelectrochemical methods are employed to systematically investigate the impacts of external charge filling in three pure wurtzite CdSe/CdS core/shell nanocrystals (NCs) with different shell thicknesses. We observed that electrons can penetrate the thick CdS shell and inject into the conduction band with an abnormal brightening, while holes are blocked. The formed negative trions result in a different spectral shift according to the size of the NCs, with a redshift of 3.7 nm for 12.5 nm NCs and almost no movement for 23.4 nm NCs. Meanwhile, due to the formation of biexcitons, a variational spectral blueshift with the NCs' size can be determined in time-resolved photoluminescence spectroscopy. This indicates that the binding energy of both biexcitons and negatively charged excitons can be regulated by controlling the shell thickness. Extra charges can also be used to activate/passivate trap states, thereby confirming that the 12.5 nm sample has better surface/interface quality.