Effective medium approach for nanoparticles in colloidal and photonic crystals

Photonic crystals are periodic structures of alternating high/low refractive index domains made of transparent materials. Those crystals can be non-transparent for a particular wavelength range due to multiple reflections and interference in the crystal. Theoretical calculations demonstrate that for fcc (face cubic centred) crystals the ratio between the refractive indices of the different domains must be higher than 2.8 to form a photonic crystal with bandgap. These crystals are used as filters for electro-magnetic radiation, e.g. infrared filters. The filter wavelength depends on the domain size and the refractive index difference between the domains.

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