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Nanocrystalquantum dots (QDs) are attractive materials for applications as lasermedia because of their bright, size-tunable emission and the flexibilityafforded by colloidal synthesis. Nonradiative Auger recombination,however, hampers optical amplification in QDs by rapidly depletingthe population of gain-active multiexciton states. In order to elucidatethe role of Auger recombination in QD lasing and isolate its influencefrom other factors that might affect optical gain, we study two typesof CdSe/CdS core/shell QDs with the same core radii and the same totalsizes but different properties of the core/shell interface (“sharp”vs “smooth”). These samples exhibit distinctly differentbiexciton Auger lifetimes but are otherwise virtually identical. Thesuppression of Auger recombination in the sample with a smooth (alloyed)interface results in a notable improvement in the optical gain performancemanifested in the reduction of the threshold for amplified spontaneousemission and the ability to produce dual-color lasing involving boththe band-edge (1S) and the higher-energy (1P) electronic states. Wedevelop a model, which explicitly accounts for the multiexciton natureof optical gain in QDs, and use it to analyze the competition betweenstimulated emission from multiexcitons and their decay via Auger recombination.These studies re-emphasize the importance of Auger recombination controlfor the realization of real-life QD-based lasing technologies andoffer practical strategies for suppression of Auger recombinationvia “interface engineering” in core/shell structures. [ABSTRACT FROM AUTHOR]