Three photoluminescence (PL) bands at 340–370, 400–430, and 740 nm were observed at room temperature ina-Si:H:O films fabricated by plasma enhanced chemical vapor deposition without any postprocessing. The violet-blue emission is very strong and stable, and its intensity is closely related to the oxygen content in the films, which can be controlled by the applied dc biases on the sample substrates during deposition. The first two PL peaks are ascribed to Si–O related species, and the last one to the quantum size effect of the nanocrystallites embedded in thea-Si:H:O matrix. ©1997 American Institute of Physics.