FZ silicon samples were multi-implanted with He ions at energies ranging from 0.8 MeV to 1.9 MeV. The dose was 5×1016 He cm−2 for all high energies but 0.8 MeV (3×1016 He cm−2). After implantation, the wafers were submitted to different annealing processes in an Argon atmosphere (A samples: 900 °C and 700 °C for 2 h; B sample 550 °C for 14 h) to optimize both density and size of cavities in order to reach a structure potentially light emitting like that of porous silicon. The samples were studied by cross section transmission electron microscopy (XTEM) and photoluminescence spectroscopy. XTEM results showed that a very thick region containing cavities has been obtained by a multi step implantation and that an annealing at low temperature is sufficient to recover the implantation damage. PL spectra arising from different depths have been obtained. PL results confirm that silicon in the region containing the highest density of cavities remains crystalline with a sufficiently low defect density for optoelectronic applications.