Abstract
Abstract Understanding and optimising the mechanisms of generation and extraction of hot carriers in plasmonic heterostructures is important for applications in new types of photodetectors, photochemistry and photocatalysis, as well as nonlinear optics. Here, we show using transient dynamic measurements that the relaxation of the excited hot-carriers in Au/Pt hetero-nanostructures is accelerated through the transfer pathway from Au, where they are generated, to Pt nanoparticles, which act as a hot-electron sink. The influence of the environment on the dynamics was also demonstrated. The time-resolved photoluminescence measurements confirm the modified hot-electron dynamics, revealing quenching of the photoluminescence signal from Au nanoparticles in the presence of Pt and an increased photoluminescence lifetime. These observations are signatures of the improved extraction efficiency of hot-carriers by the Au/Pt heterostructures. The results give insight into the time-dependent behaviour of excited compound nanoscale systems and provide a way of controlling the relaxation mechanisms involved, with important consequences for engineering nonlinear optical response and hot-carrier-assisted photochemistry.
Highlights
Optical properties of plasmonic nanoparticles have been extensively studied from both fundamental and application points of view
Through photocatalytic transformations stimulated by hot electrons, it was inferred that in such hetero-structured nanoparticles, the light absorption in a plasmonic nanoparticle due to the localized surface plasmons (LSPs) excitation efficiently creates hot electrons, which are transferred to a catalytic nanoparticle [10]
The in-depth study of the morphology of the hetero-nanoparticles, including transmission electron microscope (TEM) images, energy-dispersive X-ray spectroscopy (EDS) measurements and elemental maps of their composition can be found in our previous papers [19, 20]
Summary
Optical properties of plasmonic nanoparticles have been extensively studied from both fundamental and application points of view. We investigate the hot-carrier dynamics in chemically-derived Au/Pt composite nanoparticles supported on silica (SiO2) spheres, using time-resolved optical pump–probe and time-resolved photoluminescence (PL) spectroscopy, accessing both early stages of the dynamics before hot-electron thermalisation takes place, as well as the relaxation of thermalised electron gas in plasmonic hetero-nanoparticles These nanoparticles exhibit an increased photocatalytic performance in photodegradation experiments of organic dyes via the generation of reactive oxygen species in water-based solvents [20]. The time-resolved PL measurements reveal a quenching of the PL signal from the Au nanoparticles in the presence of Pt and an increase in the PL lifetime, linked to charge separation in these heterostructures These results confirm the influence of the composition and surroundings on the hotelectron relaxation processes in bimetallic photocatalytic nanoparticles, important for rational design of plasmonic photocatalysts and composites with designed nonlinear optical response
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