Au implantation at 32 keV into Si(100), in a fluence range of1 × 1015–1 × 1017 cm−2, has been used to produce a gold-rich damaged Si layer of thickness around 30 nm. Localrecrystallization of this layer, induced by 1.5 MeV Au irradiation, to a fluence of1 × 1015 cm−2, has been studied using Raman scattering, photoluminescence (PL) and x-rayphotoemission spectroscopy (XPS). For a sample with a low energy Au fluence of5 × 1015 cm−2, the MeV Au irradiation has been found to result in Si nanocrystal (NC) formation. Thesize of the NCs, as estimated from the PL data, has been found to be about 4 nm, whichagrees well with the result of a thermal spike model calculation. Annealing of the sample at500 °C resulted in an enhanced PL signal, without any significant shift in peak position, indicating anincrease in the local concentration of the NCs. In the case of samples with an initial Au fluence above1 × 1016 cm−2, the MeV Au irradiation has been found to result in better overall recrystallization of theamorphous layer, with silicide formation as observed by XPS. However, there was no PLsignal, indicating the absence of Si NCs in the system. The results suggest that the initialamorphizing Au fluence plays a crucial role in Si NC formation induced by MeV ionirradiation.