Abstract: A process is provided for forming a silicon material which exhibits room temperature photoluminescence and/or electroluminescence. It comprises the steps of implanting silicon ions into a silicon oxide (SiO.sub.2) substrate and subsequently annealing the substrate at an elevated temperature for a period such as to bring about Si nanocrystal formation, the nanocrystals being dispersed through the SiO.sub.2 substrate. Photoluminescence of visible light from the resulting substrate is induced on irradiation of the substrate with e.g. ultraviolet light, and the substrate can also be incorporated into an electroluminescent device. The process is characterised by the features of implanting silicon ions at a dose from 1.times.10.sup.17 /cm.sup.2 to less than that required to produce saturation and by the use of an implantation energy of 100 keV or more. The resulting silicon nanocrystals dispersed through the SiO.sub.2 substrate have an average particle size of about 30 .ANG..