The transition between plasmon resonance and photoluminescence in coinage metal and alloy nanoclusters (NC) is controlled by surface charge, core composition, and surface ligand type

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The transition regime from plasmon resonant nanoparticles to photoluminescent nanoclusters (NC) in gold is at a size 2-3 nm, where neither of these optical features is pronounced, is still poorly understood. All previous studies on this topic focused on metal-organic NC, capped with organic ligands and primarily discussed particle size effects. However, to which extent this phenomenon is also ruled by I) the number of valence electrons in the cluster, II) the energy of the contributing orbitals, or III) the polarizability of the electronic system is still scarcely understood. Thereto, size-controlled ligand-free, fully inorganic colloidal NC derived from laser fragmentation in liquids are ideal model materials. We will elucidate how electron-injecting and electron-withdrawing agents affect the transition regime discriminating A) weak charge transfer effects by ions B) strong but delocalized charge transfer from electron-rich supports like graphene, and C) strong, localized but ambivalent effects from covalently bound (Au-S) organic ligands. Additionally, element-specific features like bandgap energy and polarizability will be varied within a homologous coinage metal NC series of Au, Ag, and Cu, including AgAu and CuAu alloy NCs with of solid solution and segregated metal core ultrastructure. We will examine how doping of gold with another coinage metal with different orbital energy and polarizability affects the transition regime and how it is correlated with molar fraction and elemental mixing.