Steady-state and time-resolved near-infrared photoluminescence of [M1Ag24(SR)18]n− (M = Ag, Au, Pt, Pd, Ni) nanoclusters

Abstract

Silver nanoclusters (NCs) of atomic precision are attractive in terms of optical properties, and among the reported NCs, the thiolate (SR)-protected [Ag₂₅(SR)₁₈]⁻ serves as a model system for uncovering how the electronic structure dictates light emission. Here, we examine the effect of substituting the central Ag atom in [Ag₂₅(SR)₁₈]⁻ with Au, Pt, Pd, or Ni (note: 2− charge for Pt, Pd and Ni doped NCs). Combining steady-state, time-resolved, and oxygen-dependent photoluminescence (PL) spectroscopic studies, we show that dopants introduce distinct electronic effects that affect optical absorption and emission, and that all cases exhibit predominant phosphorescence in the near-infrared region. The incorporation of isoelectronic gold greatly enhances radiative triplet emission, yielding an unusually high quantum yield, whereas Pt or Pd substitution favors nonradiative decay despite retaining the 8-electron closed–shell superatomic configuration by charge compensation. Finally, Ni doping produces a redshift in luminescence while the other dopants lead to a blueshift compared to that of Ag₂₅. Taken together, these results reveal how single-atom substitution modulates both radiative and nonradiative pathways, establishing the doped MAg₂₄ nanoclusters as a versatile platform for tuning near-infrared photophysics at the atomic level.