In this work, FeSi2 precipitates were formed in Si by iron implantation using a metal vapor vacuum arc ion source. Transmission electron microscopy (TEM) was used to determine the crystal and defect structures of the implanted samples. It was found that the implantation temperature played an important role on the shape and phase formation of the FeSi2 precipitates, as well as the formation and distribution of the dislocation loops. When implantation was performed at an elevated temperature of about 380°C, there were a lot of dislocation loops formed and only β-FeSi2 precipitates were observed. When implanted at a low temperature of about -100°C followed by a dual step annealing process, the samples were found to be free of dislocation loops, and γ-FeSi2 and β-FeSi2 precipitates coexisting and coherent with the silicon substrate were observed. Photoluminescence (PL) spectra of different line shapes from these implanted samples were observed. By combining the PL and TEM results, the origins of the PL peaks in different samples could be distinguished and identified to be from β-FeSi2 precipitates or from crystal defects in the samples.