Light Up a Nanocluster

ABSTRACT Atomically precise metal nanoclusters (MNCs) have emerged as tailorable luminescent materials with visible to near‐infrared emission modulated by core (kernel) size, metal composition, and ligand engineering. These ultrasmall clusters exhibit discrete quantum‐confined electronic states with strong spin–orbit coupling (SOC), enabling diverse emission pathways. Current research focuses on elucidating emission mechanisms and developing strategies to enhance fluorescence quantum yields. In this review, we emphasize structure–photoluminescence (PL) correlations and the underlying excited‐state origins of luminescence: (i) coinage‐metal clusters display multiple emissive channels—including prompt fluorescence, room‐temperature phosphorescence, and TADF; (ii) the electronic gap and thus emission energy is directly governed by core size and metal identity, with core shrinkage and enhanced SOC generally inducing red‐shifts; and (iii) ligand shell properties (identity/rigidity/packing) control charge‐transfer pathways and nonradiative decay, while heterometal doping or rigidification modulates state ordering to brighten emission without necessarily shifting band positions. Importantly, many clusters exhibit dual‐emission behavior. We propose a coupled core–shell emissive‐state model in which one band originates from metal‐core excitation and the other from a ligand‐ or motif‐centered charge‐transfer state. Finally, we outline future challenges: dissecting core versus shell contributions to PL and boosting quantum efficiency through targeted control of cluster composition and ligand shell. Progress on these fronts is crucial for the rational design of next‐generation cluster emitters.