We have characterized dc-excited light-emitting properties of monodispersed silicon (Si) nanocrystallites (nc-Si) synthesized by pulsed laser ablation in inert background gas. In a case where the monodispersed nc-Si were passivated by an indium oxide (In2O3) layer without breaking the vacuum, the electroluminescence (EL) spectrum had a narrow bandwidth of 0.15 eV peaked at slightly higher energy region (1.17 eV) than the bulk Si energy gap (1.11 eV), at room temperature. On the other hand, broad visible EL (peak: 1.7 eV, bandwidth: 0.46 eV) appeared when the monodispersed nc-Si were exposed to air before In2O3 passivation. These light-emitting mechanisms are discussed in relation to quantum confinement effects and oxide-related emission centers. (C) 2002 Elsevier Science B.V All rights reserved.