Synergy Between LSPR and Energy Transfer in Ultrasmall Au Nanoclusters Stabilized on Plasmonic Ag@SiO₂ Nanoantenna Supports: Implication for Photocatalysis

Gold nanoclusters (Au NCs) have been attractive photosensitizers for many light-driven catalytic reactions due to their discrete electronic structure in the visible region. However, due to their ultrasmall sizes, they possess low stability; often, metal oxide and mesoporous supports are used to stabilize these nanoclusters. In this study, plasmonic Ag@SiO2 nanotriangle (NT) light antennas are used as supports, and the optical interactions between silver nanotriangles and Au NCs are comprehensively investigated. The Ag@SiO2–Au nanocomposite is synthesized by coating Au NCs on Ag@SiO2 using a branched polyethylenimine (BPEI) linker. Upon coating Au NCs on Ag@SiO2, the photoluminescence (PL) peak of Au NCs also blue-shifts while displaying faster decay in their excited state lifetimes, suggesting that the Ag NTs and Au NCs are optically coupled. To understand these interactions, different amounts of Ag@SiO2 NTs are added to Au NCs, and a decrease in the PL intensity of the Au NCs is observed. Using Stern–Volmer analyses, we reveal that this PL quenching is dynamic, and the energy from Au NCs is resonantly transferred to silver nanotriangles. Further, by employing Ag NTs with different surface plasmon resonance (SPR) peaks, we show that the shift in the Au NCs PL is dependent on the spectral overlap. By varying the SiO2 shell thickness from 7 to 31 nm and keeping the same degree of spectral overlap, we demonstrate that the PL quenching is distance dependent. The PL quenching in samples containing thick SiO2 (∼31 nm) reveals that the quenching occurs beyond the Förster resonance energy transfer (FRET) radius (∼20 nm) and suggests that the mechanism involves nanosurface/nanovolume energy transfer (NSET/NVET) that has been previously observed in hybrid plasmonic systems. These hybrid Ag@SiO2–Au nanocomposites have great potential for photocatalytic applications; therefore, a deeper understanding of energy transfer dynamics is critical for their growth in catalysis.