The dispersions of silver nanoparticles display intense
colors due to the plasmon resonance absorption. The surface
of a metal is like a plasma, having free electrons in the
conduction band and positively charged nuclei. Surface Plasmon resonance is a collective excitation of the electrons in
the conduction band; near the surface of the nanoparticles.
Electrons are limited to specific vibrations modes by the
particle’s size and shape. Therefore, metallic nanoparticles
have characteristic optical absorption spectrums in the UV-Vis
region