Changhyun Joo

Magic-sized clusters (MSCs) serve as well-defined model systems for investigating surface-related photophysical properties due to their atomically precise structures and monodispersity. However, indium phosphide (InP) MSCs suffer from an extremely low photoluminescence quantum yield (PLQY < 1%) due to persistent surface trap states, which not only limit their utility but also hinder a fundamental understanding of their surface chemistry and photophysics. Herein, we introduce a surface-engineering strategy that overcomes this limitation by enabling the controlled in situ HF generation via Friedel-Crafts acylation chemistry, achieving a record-high PLQY of 18.1%. Comprehensive surface analyses reveal that the enhancement arises from phosphonate ligand exchange and surface oxide removal. These modifications suppress charge carrier trapping and inhibit exciton thermal quenching at room temperature. Moreover, the altered surface environment leads to red-shifted and broadened emission, not due to size heterogeneity but rather to surface-dependent electronic states in InP MSCs. Density functional theory simulations support this mechanism by demonstrating a reduced trap state density near the valence band edge and revealing that the presence of isomeric surface configurations with slightly different energy levels is responsible for the observed spectral broadening. These findings provide a molecular-level understanding of surface-dependent excitonic behavior and establish an effective strategy for overcoming the intrinsic limitations of luminescence efficiency in InP MSCs.