Iron implantation into Si using a metal vapor vacuum arc ion source has been carried out either at a low temperature (LT) of about −100 °C or at an elevated temperature of about 380 °C, to synthesize nanometer scale β-FeSi2 precipitates in Si. The samples were characterized using transmission electron microscopy (TEM) and photoluminescence (PL). The TEM results showed that while there were plenty of dislocation loops in the high temperature implanted sample, no dislocation loop was observed in the LT implanted sample. From the differences in the PL spectra, in conjunction with the 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.