Quantum Shell in a Shell: Engineering Colloidal Nanocrystals for a High-Intensity Excitation Regime

Many optoelectronic processes incolloidal semiconductornanocrystals(NCs) suffer an efficiency decline under high-intensity excitation.This issue is caused by Auger recombination of multiple excitons,which converts the NC energy into excess heat, reducing the efficiencyand life span of NC-based devices, including photodetectors, X-rayscintillators, lasers, and high-brightness light-emitting diodes (LEDs).Recently, semiconductor quantum shells (QSs) have emerged as a promisingNC geometry for the suppression of Auger decay; however, their optoelectronicperformance has been hindered by surface-related carrier losses. Here,we address this issue by introducing quantum shells with a CdS-CdSe-CdS-ZnScore-shell-shell-shell multilayer structure.The ZnS barrier inhibits the surface carrier decay, which increasesthe photoluminescence (PL) quantum yield (QY) to 90% while retaininga high biexciton emission QY of 79%. The improved QS morphology allowsdemonstrating one of the longest Auger lifetimes reported for colloidalNCs to date. The reduction of nonradiative losses in QSs also leadsto suppressed blinking in single nanoparticles and low-threshold amplifiedspontaneous emission. We expect that ZnS-encapsulated quantum shellswill benefit many applications exploiting high-power optical or electricalexcitation regimes.