Hydrogenated Si nanocrystals were performed by high-dose (51017 cm-2) low-energy (24 keV) H+ ion implantation of silicon-on-insulator (SOI) layers. The formation of the nanocrystalline phase was observed in the as-implanted samples and in those annealed at the temperature of 200-400o C. Both the Raman shift and the broadening of the phonon peak corresponded to Si nanocrystals with the diameters ranging from ~2 to ~3 nm. The room-temperature photoluminescence (PL) peaked at 1.58 - 1.64 eV was observed at room temperature. The PL peak energy corresponded to the energy of quantum confined exciton in the Si nanocrystals with the diameters mentioned above. The PL intensity had the bell-shaped dependence on the measurement temperature and had its maximum near 150 K. The estimated thermal activation energy of the PL was about 12.1 meV and was in good accordance with the singlet-triplet splitting energy of the exciton states.