Exciton interactions and dynamics are the most important factors determining the exceptional photophysical properties
of semiconductor quantum dots (QDs). In particular, best performances have been obtained for ingeniously engineered
core/shell QDs. We have studied two factors entering in the exciton decay dynamics with adverse effects for the
luminescence efficiency: exciton trapping at surface and interface traps, and non-radiative Auger recombination in QDs
carrying either net charges or multiple excitons. In this work, we present a detailed study into the optical absorption,
fluorescence dynamics and quantum yield, as well as ultrafast transient absorption properties of CdSe/CdS,
CdSe/Cd0.5Zn0.5S, and CdSe/ZnS QDs as a function of shell thickness. It turns out that de-trapping processes play a
pivotal role in determining steady state emission properties. By studying the excitation dependent photoluminescence
quantum yields (PLQY) in different CdSe/CdxZn1-xS (x = 0, 0.5, 1) QDs, we demonstrate the different role played by hot
and cold carrier trapping rates in determining fluorescence quantum yields. Finally, the use of global analysis allows us
untangling the complex ultrafast transient absorption signals. Smoothing of interface potential, together with effective
surface passivation, appear to be crucial factors in slowing down both Auger-based and exciton trapping recombination
Renato Bozio, Marcello Righetto, and Alessandro Minotto, "Effects of surface and interface traps on exciton and multi-exciton dynamics in core/shell quantum dots," Proc. SPIE 10348, Physical Chemistry of Semiconductor Materials and Interfaces XVI, 1034816 (Presented at SPIE Nanoscience + Engineering: August 09, 2017; Published: 24 August 2017); https://doi.org/10.1117/12.2273713.
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