Fe+ ions were implanted in Si(100) and subsequently annealed. The samples were characterised by Rutherford backscattering spectrometry (RBS), transmission electron microscope (TEM), transmission electron diffraction (TED), photothermal deflection spectroscopy (PDS), and photoluminescence (PL). Formation of beta -FeSi2 precipitates in Si after annealing at 850 degreesC and their specific orientation of < 202 > beta\\< 111 > Si and < 010 > beta\\< 011 > Si were confirmed by TEM. A weak optical absorption above 0.8 eV corresponding to the band-gap of beta -FeSi2 was detected by PDS, and a broad PL at 0.8 eV was also observed. The intensity of this PL line was enhanced remarkably with additional annealing at the same temperature in a H-2 atmosphere. However, a number of defects were produced in the near surface region by ion-implantation. Since defects from PL were produced, in particular originating from dislocations in Si, is also located at approximately 0.8 eV, the origin of the PL is still uncertain. In order to eliminate the PL from dislocations in Si, a formation method of beta -FeSi2 precipitates in SiO2 films on Si was tried by co-implantation of Fe+ and Si+ ions with a dose at the stoichiometrical ratio of 1:2. However, part of implanted Fr diffused out from the implanted region after annealing. Thus, co-implantation of both Fe+ and Si+ ions in SiO2 is not an appropriate way to form beta -FeSi2 precipitates in SiO2.