3 years ago

First-Principles Study of Fluorescence in Silver Nanoclusters

First-Principles Study of Fluorescence in Silver Nanoclusters
Samuel L. Brown, Erik K. Hobbie, Dmitri S. Kilin, Sergei Tretiak
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 thermalizations toward the band edges is modeled using Redfield theory, and the corresponding time-integrated emission is calculated. Peak emission near 610 nm is found, consistent with experimentally reported PL in AgNCs. This work gives further insight into the recombination kinetics of AgNC and can be used to aid in tailoring their optical properties to maximize fluorescence efficiency and tunability.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04870

DOI: 10.1021/acs.jpcc.7b04870

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