Tuning the Charge Carrier Dynamics via Interfacial Alloying in Core/Shell CdTe/ZnSe NCs

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 (similar to 220 degrees C) reaction temperature the effect of interfacial alloying is less pronounced. Interestingly, as the reaction temperature is sequentially changed between 220 and 280 degrees C during core/shell synthesis a blue -shifted short-lived (similar to 10 ns) emission appears accompanied by the normal long-lived (similar to 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 (similar to 280 degrees 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.