The measurements of optical transmission, photoluminescence (PL), and PL excitation (PLE) of Si-implanted silicon nitride thin films annealed at various temperatures have been conducted. A red PL band at similar to 680 nm is largely enhanced by the Si implantation followed by thermal annealing. The excitation of the red PL band is attributed to the transitions between the Si-bond-related states of sigma and sigma(*), while the emission of the red PL band is believed to be from the radiative recombination associated with defect states which are largely increased by the Si ion implantation. Another excitation transition contributing to the red PL band, which is evidenced by the PLE peak at 425 nm, emerges after the annealing at 1100 degrees C, and it is attributed to the formation of stable Si nanoclusters.