The nanocrystalline silicon embedded in silicon dioxide has been successfully prepared by post heat treatment for SiOx∶H.We have found that each strong photoluminescence spectrum from a-SiOx∶H consists of two Gaussian components.One is a main broad peak which redshifts with the increase of annealing temperature and the other is a shoulder remaining at about 835 nm.In conjunction with infrared and micro-Raman spectra,the possible origins of the two bands are discussed.The peaks around 850 nm after annealing at 1170℃ are associated with the precipitation of nanocrystalline silicon,and this supports the quantum confinement effect.