Nanocrystalline Si (nc-Si) embedded in a SiO2 matrix, fabricated by plasma CVD and a subsequent post-treatment shows a broad red photoluminescence (PL). In this paper, the effects of annealing temperature, atmosphere and time on the red PL from 1.75 to 1.5 eV have been investigated in detail. It is found that the spectral shift and the PL intensity from 1.75 to 1.5 eV show a strong and unique dependence on annealing conditions. For a PL approximately 1.75 eV, upon 400 ℃ forming gas annealing, the spectral shift and the peak intensity versus accumulation annealing times show a novel temporal oscillation. This unique dependence and the novel temporal oscillation behavior, which have not been reported in porous silicon, exclude nc-Si itself as the source of the red PL. Instead they favor oxygen thermal donors (TDs)-like defect states as PL centers. This is in consensus with our earlier results of defect studies using electron spin resonance in this system. Furthermore, two PL centers in this red PL were distinguished according to their variance in annealing temperature- and time-dependence. The spectral change between 1.5 and 1.75 eV upon annealing conditions can be qualitatively explained by using the formation and annihilation kinetics of two oxygen TDs-like defect state.