As
luminescence applications of colloidal semiconductor nanocrystals
push toward higher excitation flux conditions, there is an increased
need to both understand and potentially control emission from multiexciton
states. We develop a spectrally resolved correlation method to study
the triply excited state that enables direct measurements of the recombination
pathway for the triexciton, rather than relying on indirect extraction
of rates. We demonstrate that, for core–shell CdSe–CdS
nanocrystals, triexciton emission arises exclusively from the band-edge
S-like state. Time-dependent density functional theory and extended
particle-in-a-sphere calculations demonstrate that reduced carrier
overlap induced by the core–shell heterostructure can account
for the lack of emission observed from the P-like state. These results
provide a potential avenue for the control of nanocrystal luminescence,
where core–shell heterostructures can be leveraged to control
carrier separation and therefore maintain emission color purity over
a broader range of excitation fluxes.
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