Tuning the charge carrier dynamics via interfacial alloying in core/shell CdTe/ZnSe NCs

Abstract

For core/shell semiconducting nanocrystals the interface plays an important role governing the charge carrier dynamics. This work focuses on CdTe/ZnSe spherical core/shell NCs where the optical spectra and charge carrier dynamics can be tuned depending on the synthetic conditions employed. When ZnSe is coated on top of CdTe core at nominal (∼220 °C) reaction temperature the effect of interfacial alloying is less pronounced. Interestingly, as the reaction temperature is sequentially changed between 220 and 280 °C during core/shell synthesis a blue-shifted short-lived (∼10 ns) emission appears accompanied by the normal long-lived (∼36 ns) core/shell emission. This blue-shifted emission has its origin in the interfacial alloyed layer which forms due to ionic diffusion. At elevated temperature (∼280 °C) this blue emission diminishes with an increase in the overall QY for the core/shell emission around 700 nm. Ultrafast transient absorption spectroscopy reveals the interplay of carrier population dynamics in first and higher excitonic states which are subsequently affected by interfacial alloying.