First-Principles Study of Fluorescence in Silver Nanoclusters

Abstract

Mechanisms of efficient fluorescence from biocompatible, ligand-protected silver nanoclusters (AgNC) are explored with an atomistic model of an icosahedral shaped AgNC passivated with 12 cytosine molecules representing single-stranded DNA. Spin-resolved density-functional theory with varying constraints to the total charge was used as a simulation probe to explore the electronic structure and photoluminescence of AgNCs. Visible photoemission in AgNCs is modeled through a synergy of radiative and nonradiative photoinduced dynamics computed by a combination of density matrix and density functional methods with explicit treatment of spin polarization. The ab initio computed charge-to-total energy correlation, Etot(ΔN), of the modeled AgNC shows an approximate 2.2 eV discontinuity at a charge of ΔN = 5, which correlates with the DFT calculated band gap and with concept of superatom with closed shell valence electron count [PNAS 2008, 105, 9157]. UV photoexcitation of this cationic model followed by cascade th...