We show the formation and explain the optical origin of self-organized metallic photonic crystals buried in thin films.

Silver nanoparticles were created inside mesoporous titania thin films by different reduction processes. We investigated the influence of the reduction method on the colour and photochromism of these amorphous TiO₂ films. The results highlight brown films by optical reduction, gray films by thermal reduction, and red, purple or orange films by chemical reduction. The different size distributions and localizations of the nanoparticles, characterized by UV-visible spectroscopy and electron microscopy, give various photochromic behaviours when exposed to visible laser light. We especially report the bleaching of different film colours under laser exposure.