A single-step, room temperature photolithographic route to fabricate periodic metallodielectric microstructures is reported. Ag nanoparticles in organosiloxane sols were first generated through the well-established method of AgCl photoreduction. Evolution of the shape, size and distribution of Ag nanoparticles in the fluid sols upon irradiation with white light was characterised in detail through optical extinction spectroscopy and transmission electron microscopy. Ag nanoparticles were extremely stable in sols, which were subsequently processed into films, gels and monoliths. The application of these composites in the fabrication of optical gratings containing a uniform distribution of Ag nanoparticles was demonstrated through both photomask and interference lithographic techniques. This technique provides accessible routes to a range of metallodielectric microperiodic structures, which could enable experimental verification of theoretically predicted optical properties including enhanced photonic band gaps.