We characterize energy transfer between luminescent 1.5 nm diameter gold nanocrystal (AuNC) acceptors and three structurally/functionally-distinct classes of emissive donors including organic dyes, metal chelates and semiconductor quantum dots (QDs). Energy transfer efficiencies within the donor-AuNC assemblies were evaluated with steady-state and time-resolved measurements. Donor quenching was observed for every donor-acceptor pair although AuNC sensitization was only observed from metal-chelates and QDs. Results were analyzed with Förster’s dipole-dipole coupling model (FRET) and dipole-metal damping models including nanosurface energy transfer (NSET) and nanovolume energy transfer (NVET). FRET dramatically underestimated energy transfer efficiencies while the damping models provided qualitatively better fits to the data although neither fully reproduces the experimental data. Analysis suggests that organic dye donor quenching without corresponding AuNC sensitization results from enhanced intersystem crossing between dye singlet and triplet states driven by AuNC magnetic dipoles. We further consider factors that account for the unique electronic properties of the ultra-small luminescent AuNCs including the high excited state densities, rapid dephasing time and strong electron confinement as well as paramagnetic properties. Overall, the results provide insight into requirements necessary for realizing applications based on AuNC acceptor sensitization.
Eunkeu Oh, Alan L. Huston, Andrew Shabaev, Alexander L. Efros, Marc Currie, Kimihiro Susumu, Konrad M. Bussmann, Ramasis Goswami, Fredrik K. Fatemi, and Igor L. Medintz, "Energy transfer sensitization of luminescent gold nanoclusters: more than just the classical Forster mechanism (Conference Presentation)," Proc. SPIE 9722, Colloidal Nanoparticles for Biomedical Applications XI, 97220F (Presented at SPIE BiOS: February 14, 2016; Published: 28 April 2016); https://doi.org/10.1117/12.2212733.4848770159001.
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