We have fabricated light‐emitting nanocrystallites embedded in ana‐Si:H matrix using a conventional plasma‐enhanced chemical‐vapor‐deposition system. It was found that the photoluminescence properties are directly related to the deposition parameters. The quantum size effect model is proposed to explain the photoluminescence. Two structural prerequisites are proposed for this kind of films to exhibit effective light emission: One is an upper limit for mean crystallite size of about 3.4 nm, the other is an upper limit for crystallinity of about 30%. ©1995 American Institute of Physics.