The color of finely dispersed nanoparticles

We discuss the dependence of the color of low-concentrated nanoparticle sys tems on particle size and mass concentration for Ag, Au and TiN nanoparticl es, which exhibit a surface plasmon polariton resonance in extinction spect ra. Comparison is made with color data obtained for Ag and Au colloidal sus pensions. When particles lump into aggregates, the splitting of the surface plasmon r esonance into new resonances affects the extinction of light and, hence, th e color of the particle assembly. This is demonstrated for aggregated collo idal suspensions of Ag and An nanoparticles. Finally, for highly concentrated assemblies such as pigment films, we discu ss the dependence of the color in diffuse reflectance and transmittance acc ording to Kubelka and Munk (P. Kubelka, F. Munk: Z. Techn. Phys. 12, 593 (1 931)), and extend this model by using optical properties of aggregates of s pheres.