Abstract: There are provided mesoporous silica materials containing in their pores stabilized clusters of silicon atoms, of size 2 nanometers or less, and capable of photoluminescence to emit fast photons. They are prepared by chemical vapour deposition of silicon or a silicon precursor such as disilane, under soft conditions such as temperature of 100-150° C., into the mesopores of silicate films which have mesoporous channels prepared by growth of the films using a template to control their sizes, but without removing the template residues from the films prior to the chemical vapour deposition. The template residues serve to limit the size of the silicon clusters which conform. The use of the soft conditions on CVD retains the template residues in an intact, substantially unchanged form. The resultant films have clusters of silicon, of 2 nanometer size or less, anchored to the mesopores, and air stable, so that they can be used in optoelectronic devices in conjunction with standard silicon semiconductors.