The effects of pore size distribution in porous glasses on the photoluminescence of nanosized Si clusters and of the humidity on the sample dimensions have been investigated. Increase of the pore size brings about the blueshift of the emission peak. In the spectra, geminate and distant components of the emission have been resolved. The humidity influences the dimensions of the samples due to the competing of chemical bonding forces and capillary forces. ©1998 American Institute of Physics.