Resolving Single-Particle Absorption and Scattering by Plasmonic Magnesium Nanoparticles.

Magnesium nanoparticles have emerged as a promising plasmonic material due to their low cost and biocompatibility, yet their optical absorption at the single-particle level is largely uncharacterized. While ensemble extinction measurements of 170 nm Mg spheroids show a broad extinction spectrum, we demonstrate through correlated single-particle dark-field scattering and photothermal absorption spectroscopies that individual nanoparticles support well-defined plasmon resonances in absorption and scattering. We found that the peaks in absorption and scattering occur at a similar wavelength average, with absorption consistently broader than scattering. Simulations reproduce these trends and confirm that the broader absorption line width arises from the large dispersion of the real part of Mg's dielectric function. These findings provide fundamental insights into the spectral differences in absorption and scattering by Mg nanoparticles and demonstrate the necessity of single-particle measurements for understanding their optical response, crucial for optimizing performance in diverse plasmonically powered applications.