Olaf Alberto von Mankowski
Katalin Szendrei

Photonic Crystals

Photonic crystals (PCs) are ubiquitous natural objects found in beetle shells, butterfly wings, and nacre, yet at the same time promising building blocks for all-optical integrated circuits and switches moulding the propagation of light. The underlying principle however is simple: Following nature's example, beautiful colors can be imparted to inherently colorless materials by Bragg reflection taken to a larger length scale: By analogy to electronic semiconductors (the "little brothers"), photonic crystals possess photonic bandstructures including "bandgaps", the latter giving rise to light reflection and thus, color! From a materials perspective, photonic crystals feature a periodic refractive index contrast which can extend into 1, 2, or 3 dimensions. In principle, the library of materials that may constitute PCs is unlimited, rendering PCs an intriguing platform for the creation of highly colourful structures based on inherently colorless materials.

Whereas both top-down and bottom-up approaches to PC reflectors based on standard materials such as SiO2/TiO2 are well established, the fabrication of tunable structural color PCs remains a challenge. Our group pursues the fabrication of stimuli-responsive PCs based on a wide spectrum of inherently functional organic, inorganic and hybrid materials in order to create a platform translating material response into color read-out. Ultimately, this strategy will allow us to use structural color changes as an in situ probe of material transformations and reactions and therefore, as signal transduction pathway in chemooptical sensors.

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