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Colloidal Photonic Crystals: Beyond Optics, Beyond Spheres
Koen Clays

Colloidal photonic crystals are photonic crystals made by bottom-up physical chemistry strategies from monodisperse colloidal particles. The self-assembly process is automatically leading to inherently three-dimensional structures with their optical properties determined by the periodicity, induced by this ordering process, in the dielectric properties of the colloidal material. The best-known optical effect is the photonic band gap, the range of energies, or wavelengths, that is forbidden for photons to exist in the structure. This photonic band gap is similar to the electronic band gap of electronic semiconductor crystals. We show how with the proper photonic band gap engineering, we can insert allowed pass band defect modes and use the suppressing band gap in combination with the transmitting pass band to induce spectral narrowing of emission and enhanced energy transfer. We also go beyond the spherical paradigm to open ways to new crystal structures by using non-spherical colloidal particles and we add additional functionality by inserting magnetic properties, both for orienting the non-spherical particles and for magneto-optic effects.

Keywords: photonic crystal, photonic band gap, pseudo band gap, stop band, pass band, defect mode, fluorescence suppression, spectral narrowing, Förster resonant energy transfer (FRET), magneto-optics, Faraday rotation

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