Clarifying the Controversy over Defect Emission of I-III-VI₂ Nanocrystals via Pressure Engineering

I-III-VI2 semiconductor nanocrystals (NCs), such as typical AgInS2 NCs, are promising candidates for fluorescent materials because of their lower toxicity and tunable optical properties. However, a long-standing conventional dispute over the origin of defect emission of AgInS2 NCs restricts the material design and applications. Here, high pressure is introduced to distinguish the photophysical behavior of a core@shell structure of AgInS2@InSx NCs that exhibit both band-edge (BE) emission and defect emission. Compared with the well-established dopant mechanism of Ag+:CdS NCs, the decreasing relative shift of defect/BE emissions for AgInS2@InSx NCs excludes the Ag-related emission associated with radiative free-to-bound recombination that contributes to the defect emission of AgInS2 NCs. Identification by the in situ high-pressure transient spectra and comparative experiments passivated with different ligands, the donor-acceptor pair (DAP) recombination is responsible for the observed defect emission. Likewise, a narrow and strong BE emission with 5.3-fold enhancement is achieved in AgInS2@InSx NCs by pressure processing. This in turn further confirms the DAP-related origin of the defect emission. Overall, this study enables high pressure as a tool to resolve the traditional debate under ambient conditions, which facilitates the fundamental photophysical understanding for materials by design applied in solid-state lighting.