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

Abstract I–III–VI 2 semiconductor nanocrystals (NCs), such as typical AgInS 2 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 AgInS 2 NCs restricts the material design and applications. Here, high pressure is introduced to distinguish the photophysical behavior of a core@shell structure of AgInS 2 @InS x 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 AgInS 2 @InS x NCs excludes the Ag‐related emission associated with radiative free‐to‐bound recombination that contributes to the defect emission of AgInS 2 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 AgInS 2 @InS x 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.