Plasmonic nanoparticles have great potential for the design of new optical and photocatalytic materials. Recently there has been great interest in aluminum nanoparticles as they have widely tunable plasmon resonances in the visible and because of greater relative abundance of Al compared with noble metals. We have examined the ultrafast photophysics of Al nanoparticles when excited near the maximum of the plasmon resonance. Particles were synthesized under air-free conditions and have a diameter of ~100nm. Transient absorption reveals no bleaching of the steady-state plasmon band as observed in the transient spectra collected with noble metals. The photophysics of Al nanoparticles exhibit broad changes in light transmission on both ultrafast and nanosecond timescales: a net decreased transmission appears initially and maximizes by 7.5 ps, then slowly changes to a net increased transmission over a few hundred ps. We attribute these spectral signatures to the evolution of a time-dependent transient lens. While slow transient lensing has been observed with noble-metal particles and attributed to energy transfer to the surrounding medium (inducing a reduction in refractive index), ultrafast dynamics with Al particles indicate an initial positive change in refractive index that can be attributed with electron-phonon and phonon-phonon relaxation within the Al itself.

Ultrafast photophysics of plasmonic aluminum nanoparticles

253rd National Meeting (2017)

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