Germanium nanoparticle optical properties

Germanium has one of the highest refractive indices of common materials (about 4.0–5.2 from the visible to the near-infrared) and a small band gap (0.66 eV), so it absorbs strongly throughout the visible. Germanium nanospheres therefore absorb visible light efficiently and show Mie resonances, magnetic and electric dipoles, mainly in the near-infrared: about 742 nm (MD) for 150 nm and 923 nm for 200 nm spheres (table above).

About 5.2 + 2.1i at 550 nm and about 4.2 at 1550 nm, where absorption is small. The calculators use the ellipsometry data of Nunley et al. (2016), with Aspnes & Studna (1983) as an alternative.

Silicon has sharper resonances in the visible and absorbs little above about 500 nm; germanium resonates further into the infrared, absorbs strongly in the visible (useful for photothermal heating and photodetection) and has a higher index at telecom wavelengths. Compare them on the silicon page.

Yes, including simulation of the germanium nanoparticle UV-vis spectrum, optical properties of nanospheres and core–shell particles, near-field enhancement, array lattice resonances, substrates and heating; germanium is available in every calculator: near-field maps, arrays, particles on substrates and laser heating.