A method which combines polymer particle assembly, chemical infiltration and etching with an aerosol assisted deposition process is described for the fabrication of 3D inverse opal (10) structures with sub-micron periodicity and precision. This procedure not only overcomes limitations associated with slow, expensive micro-fabrication methods but also permits the tuning of refractive index contrast via the direct incorporation of photonically-active, preformed, tailored silicon nanostructures. It is demonstrated that this approach can be used to modify the photonic band gap (PBG) by effectively depositing/patterning optically active silicon nanocrystals (ncSi) onto the pore walls of a 3D inverse opal structure. This simple, yet effective method for preparing functional complex 3D structures has the potential to be used generically to fabricate a variety of functional porous 3D structures that could find application not only in new or improved photonic crystal (PC) devices but also in areas such as catalysis, separation, fuel cells technology, microelectronics and optoelectronics.