The invention relates to processes for the synthesis of 2-D and 3-D periodic
porous silicon structures and composites with improved properties having the advantages
of porous silicon and photonic bandgap materials. Photonic crystals comprise a
two dimensionally periodic or three dimensionally periodic microporous structural
matrix of interconnecting, crystallographically oriented, monodispersed members
having voids between adjacent members, and said members additionally having randomly
nanoporous surface porosity. The silicon nanofoam material shows enhanced and spectrally
controlled/tunable photoluminescence and electroluminesce and finds use as transparent
electrodes, high-lumonosity light emitting diodes (LEDs), wavelength division multiplexors,
high-active-area catalyst supports, photonic bandgap lasers, silicon-based UV detectors,
displays, gas sensors, and the like.