Environmentally friendly blue-emitting ZnSe quantum dots (QDs) are in high demand for next-generation lightemitting devices. Yet, they suffer longstanding optical instability issues under aerobic conditions. Herein, we have demonstrated the existence of oxidization or hydroxylation on the QD surface when QDs are subjected to oxygen exposure, which potentially introduces highly localized in-gap states. Those states result in a dense number of surface-related, weak-intensity "dark" exciton states at the emission edge. Remarkably, there exists a critical diameter (D c ≈ 8.5 nm) at which the deepest trap level reaches resonance with the highest occupied molecular orbital state. Beyond this critical diameter, the effects of those trap states are minimized, and the emission edge is dominated by high-intensity, bulk-to-bulk-like "bright" exciton states. The present work provides a novel strategy for designing highly stable QD emitters via size engineering, which are broadly applicable to other closely related QD systems.

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Colloidal InAs nanocrystals (NCs) are among the most promising light emitters in the short-wavelength infrared (SWIR) range. These InAs NCs are eligible to crystalize into two distinct phases, i.e., cubic zinc-blende phase and metastable hexagonal wurtzite phase. However, InAs NCs directly produced through molecular precursors unanimously exhibited zinc-blende structure, and the synthesis of their wurtzite counterparts has never been achieved. Herein, we report the first successful synthesis of high-quality wurtzite InAs NCs, which show bright SWIR photoluminescence with a tunable emission peak and high quantum yield of up to ∼37%. This is achieved by the cation exchange of Cu3As NCs with controllable size and morphology, followed by the growth of inorganic passivation layers to eliminate the possible surface trap centers. We further expand the synthesis route to wurtzite ternary InAs0.5P0.5 NCs with quasi-one dimensional confinement, which exhibit polarized SWIR emission, exploring the potential of these anisotropic NCs as efficient polarized light emitters.

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Environmentally friendly colloidal quantum dots (QDs) of groups III–V are in high demand for next-generation high-performance light-emitting devices for display and lighting, yet many of them (e.g., GaP) suffer from inefficient band-edge emission due to the indirect bandgap nature of their parent materials. Herein, we theoretically demonstrate that efficient band-edge emission can be activated at a critical tensile strain γc enabled by the capping shell when forming a core/shell architecture. Before γc is reached, the emission edge is dominated by dense low-intensity exciton states with a vanishing oscillator strength and a long radiative lifetime. After γc is crossed, the emission edge is dominated by high-intensity bright exciton states with a large oscillator strength and a radiative lifetime that is shorter by a few orders of magnitude. This work provides a novel strategy for realizing efficient band-edge emission of indirect semiconductor QDs via shell engineering, which is potentially implemented employing the well-established colloidal QD synthesis technique.