Auger
decay of multiple excitons represents a significant obstacle
to photonic applications of semiconductor quantum dots (QDs). This
nonradiative process is particularly detrimental to the performance
of QD-based electroluminescent and lasing devices. Here, we demonstrate
that semiconductor quantum shells with an “inverted”
QD geometry inhibit Auger recombination, allowing substantial improvements
to their multiexciton characteristics. By promoting a spatial separation
between multiple excitons, the quantum shell geometry leads to ultralong
biexciton lifetimes (>10 ns) and a large biexciton quantum yield.
Furthermore, the architecture of quantum shells induces an exciton–exciton
repulsion, which splits exciton and biexciton optical transitions,
giving rise to an Auger-inactive single-exciton gain mode. In this
regime, quantum shells exhibit the longest optical gain lifetime reported
for colloidal QDs to date (>6 ns), which makes this geometry an
attractive
candidate for the development of optically and electrically pumped
gain media.
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