DYNAMICS OF ENERGY TRANSFER IN LARGE ALUMINUM NANOPARTICLES: SIZE AND SURFACE DEPENDENT PHOTORESPONSES OF SOLUTION PROCESSED PARTICLES

Novel realizations of metal nanoparticles (NPs) are of continuing interest due to their unique optical properties and potential applications in optoelectronics, sensing, and catalysis. The unique and customizable optical properties of these particles make them ideally suited to act as light harvesters across the energy spectrum. Unlike bulk materials it is possible to modify metallic NP’s absorption characteristics simply by adjusting their size, shape, and medium in which they reside. Aluminum is an inexpensive earth-abundant plasmonic material and a promising alternative to noble metals for applications requiring UV sensitivity and scalability. The plasmon resonance of bulk aluminum metal falls in the ultraviolet, but the LSPRs of aluminum NPs have been tuned successfully to the visible and NIR In this work, time-resolved ultrafast broadband transient absorption spectroscopy has been used to study the relaxation dynamics associated with photoexcitation of plasmonic aluminum NP’s. Our Lab reported the first photophysical characterization of energy-transfer dynamics in large (100 nm diameter) plasmonic aluminum nanoparticles suspended in liquid isopropanol. Using a two-interface model, we find that a rapid thermal energy transfer from particle to solvent is accounted for by the presence of a compact ~4 nm native oxide layer on the aluminum nanoparticles. Size-dependent phonon “breathing”/vibrational modes are also observed as oscillations in total cross-section. We find that both the oscillation frequency and damping rate increase as the diameter of the particles decreases. Due to their rapid cooling, these particles are expected to be rather robust and could be utilized as an effective tool to engineer heat transfer rates from large particles to the surrounding medium