Visible photoluminescence (PL) can be observed ina-SiOxanda-SiOx:Halloys prepared by evaporation of SiO in ultrahigh vacuum and under a flow of hydrogen ions, respectively. The hydrogen and oxygen bonding is studied by infrared spectrometry. The hydrogen stability is followed by thermal desorption spectrometry experiments. The evolution of the PL with annealing treatments shows that the PL can be attributed to a quantum confinement effect ina-Siclusters embedded in the matrix ofa-SiOx.Hydrogen does not greatly contribute to the PL efficiency and to the thermal evolution of thea-Siclusters. ©1998 American Institute of Physics.