In this paper we analyze linear and ultrafast non-linear properties of a three-dimensional photonic crystal composed of close-packed SiO<sub>2</sub>/Au/SiO<sub>2</sub> core-shell colloidal particles. Strong coupling between incident light and surface plasmon of spherical gold microcavities appears as sharp features in observed reflectivity spectra in the visible. In a single layer of gold-shell particles, a highly directional diffraction pattern was observed with hexagonal symmetry. The non-linear dynamics of the reflectivity has been studied by femtosecond white-light pump-probe experiments. Abrupt changes limited by the instrumental time resolution, were observed in time-resolved reflection spectra while the signal recovers in about 10 ps. Ultrafast changes in reflectivity reach values as high as 20%. The results are compared with theory.
It is shown that small metallic inclusions can have a dramatic effect on the photonic band structure of diamond and zinc blende structures. In the case of silica spheres with a silver core, the complete photonic band gap (CPBG) between the 2nd-3rd bands opens for a metal volume fraction <i>f<sub>m</sub></i>≈ 1% and has a width of 5% for <i>f<sub>m</sub></i>≈ 2.5%. Absorption in the CPBG of 5% remains very small (≤ 2.6% for λ ≥ 750 nm). These findings open the door for any semiconductor and polymer material to be used as a genuine photonic crystal building block and significantly increase the possibilities for experimentalists to realize a sizeable and robust CPBG in the near-infrared and in the visible.