Raman spectra of the porous structure with intense blue emission formed on C+‐implanted silicon were examined using a 488 nm line of Ar+ laser. A Raman peak with full width at half‐maximum of 37 cm−1 was obtained at about 492 cm−1. No Raman signals related to the β‐SiC were detected. The experimental result indicates that the porous structure mainly consists of Si nanometer crystallites. The existence of β‐SiC precipitates with nanometer sizes may be beneficial to the reduction of crystallite sizes and strengthen the Si skeleton, which will lead to an increase in the energy band gap of Si to the blue light emission. Using a model of phonon confinement, the obtained Raman spectra could be fitted on the basis of Si quantum crystallites and the average crystallite size was estimated to be 1.4 nm.