The optical properties of gold and silver nanoparticles have been known for centuries, appearing in Roman glassware as well as medieval stained glass. An understanding of the phenomenon giving rise to these brilliant colors emerged in the last century: collective oscillations of conduction electrons called localized surface plasmon resonances (LSPRs) can be excited by light, leading to wavelength-dependent absorption and scattering. LSPRs have a broad technology potential as an attractive platform for surface-enhanced spectroscopies, non-bleaching labels, hyperthermal cancer therapy, waveguides, and so on. Excitingly, this light-matter interaction can be controlled by the size, shape, and dielectric environment of the nanoparticles; enabling the manipulation of LSPR energy, absorption/scattering ratio, light confinement, as well as far-field and near-field emission geometry, all important for specific applications.
Most plasmonic metals studied to date are composed of either Cu, Ag, and Au. The former two can pose significant challenges related to oxidation, the latter is often perceived as cost-prohibitive, and all three are rare. Recently, much attention has been focused on earth-abundant Al, which is an excellent plasmonic in the UV. This talk will briefly discuss colloidal Al nanoparticles as a plasmonic material, then report results on a new composition: magnesium. Mg nanoparticles are remarkably active plasmonics across the UV, Vis and NIR, as shown optically and with STEM-EELS. Surprisingly, they are stable in air for weeks owing to a self-limiting oxide layer. Colloidal Mg has potential on its own as a plasmonic structure, and can also be used as a scaffold for additional surface chemistry, sensing, and hybrid photocatalysts.