Sorbonne Université, Institut des NanoSciences de Paris,
Keywords: nanotechnology, gold nanoparticles, silver nanoparticles, plasmon, LSPR, color, printing inks, bichromatism
Summary:A key aspect of nanotechnology lies in generating new properties with conventional material, when it is reduced to sizes in the range of a few nanometers. Gold is no exception and especially when dealing with colors. Pure bulk gold is yellow, but 20 nm gold nanospheres adopt a deep ruby red color. It is the consequence of the plasmonic properties of gold. This talk will describe the fundamentals of plasmonic colors and distinguish them from the usual pigment colors used in the printing industry, and from the less-known structural colors that are based on optical interferences. We will discuss how plasmonic colors are generated in various metals and how far they can be tuned. We will explain the striking effect of bichromatism generated by some metallic nanoparticle, where a material is seen with two complementary colors when it is observed in transmission or in reflection. For example, a bichromatic material can be blue in transmission and orange with reflected light (see www.bichromatics.com) Plasmonic colors offer some unique coloring effects that can be introduced in bulk materials, in printing inks or in varnishes.