Perspective on the scintillating response of CdSe based nanoplatelets heterostructures

Abstract

We explore the effect of shell thickness on the time and spectral response of CdSe/CdS core–crown and CdSe/CdZnS core–shell nanoplatelets (NPLs) under X-ray and intense optical excitation. From their intensity-dependent spectral and timing response, we demonstrate that the exciton–exciton interaction in the bi-exciton (XX) changes from attractive to repulsive when varying the design from core/crown to thick quasi type II core/shell 2D nanostructures. We find that an additional shell layer of 0.4 nm is enough to convert the red-shifted XX emission to non- or blue-shifted emission. Under pulsed X-ray excitation, the scintillation decay dynamics reveal that multiexcitons are generated in all 2D nanostructures, whose presence can hardly be detected in the emission spectra for NPL thicknesses larger than 2 nm. We provide a numerical estimation of the number of scattering events of 35 keV electron as a function of NPL thickness, revealing that the formation of biexcitons with ultra-fast time response is more efficient in thick NPLs. However, this advantage is counterbalanced by a blue-shifted emission of that ultra-fast emission, rendering large NPLs less effective regarding the self-absorption issue.