Judith Wijnhoven
van der Waals Zeeman Instituut,
Universiteit van Amsterdam Amsterdam,the Netherlands
http://www.wins.uva.nl/research/scm
In three dimensional photonic crystals, the refractive index varies periodically on length scales comparable to the wavelength of light. This leads to exciting phenomena such as localization of light and inhibition of spontaneous emission.
To obtain a photonic bandgap (i.e. a Bragg reflection in all directions), certain requirements should be fulfilled. The constituent materials should be periodicaly structured with lattice spacings of several hundreds of nanometers and they must have a high refractive index contrast.
We have developed two kinds of photonic crystals:
Air-sphere crystals are made by filling the voids in an artificial opal with a precursor of the target material. After reaction and removing the opal a crystalline array of air spheres in a solid is left. In our case the solid materials were titania (n=2.6) and sodium cloride.
These macroporous materials are a new class of photonic crystals for the optical spectrum. Scanning electron microscopy and small-angle x-ray diffraction confirm the excellent quality of the crystals. Optical reflectivity demonstrates that the crystals are strongly photonic and nearly exhibiting photonic bandgap behavior. This type of materials has pore sizes that are much larger than those obtained by zeolites or mesoporous solids which makes them interesting for applications in, for example, catalysis.
Stichting FOM is thanked for support.