Ultrafast relaxation dynamics of aluminum nanoparticles in solution

Colloidal aluminum nanoparticles (Al NPs) can support surface plasmon resonances spanning ultraviolet to near-infrared wavelengths because of the high electron density of Al metal and the favorable position of its interband transitions. Free-standing colloidal Al particles can be synthesized using a variety of methods and suspended in solution, but there are still few investigations of its ultrafast decay processes. We used transient absorption spectroscopy (TAS) to examine the ultrafast relaxation dynamics of colloidal Al NPs suspended in ethanol. The electron-phonon (e-p) coupling times of Al NPs are equivalent or even longer than the e-p coupling times of Ag nanocubes or Au bipyramids in solution. The prolonged hot-electron transfer in Al NPs is likely due to the presence of the Al2O3 shell, which causes excited charge carrier trapping-detrapping at the metal core-oxide shell interface.