Why are you interested in the use of gold and silver? Why not the cheapest iron?

The unique electronic properties of the nanomaterials arise from their interaction with an incident electromagnetic radiation.

Plasmons are the collective oscillations of free electrons in metals. In bulk materials, with an incident light, propagating surface plasmon polariton (PSPP) can occur under certain conditions. When the metals are in nanometres range, i.e. as a nanoparticle with a comparable size of a wavelength, and are illuminated with the appropriate wavelength (to produce resonance), the particle’s free electrons participate in the collective oscillation, and it is called localised surface plasmon resonance (LSPR). LSPR in nanoparticles is strongly dependant on several factors, such as the metal type, size or shape of the nanoparticle, and also to the surrounding media. The existence of the LSPR makes that the nanoparticle behaviour changes drastically; for example, their optical properties will be greatly affected.

Due to the formation of LSPR in metallic nanoparticles, the electromagnetic field near the nanoparticle’s surface is strongly increased and rapidly falls off with distance. Furthermore, noble metal nanoparticles present an extinction cross-section that can be much larger than their geometrical size. The optical extinction shows a maximum at the surface plasmon resonance frequency, and for gold and silver nanoparticles, it is located at visible wavelengths. That is why you can have different colours with them! For example, you can do magnetic nanomaterials with iron, but they used to present a black colour. Other metals and their combination, as well as their oxidation states, may give different and exciting properties.

Are we in the new metal ages?