Blue luminescence at about 431 nm is obtained from epitaxial silicon after C+implantation, annealing in hydrogen ambience and chemical etching sequentially. When annealed in nitrogen ambience and etched accordingly, there is a much narrower peak at about 430 nm. During C+implantation, C= O compounds are introduced into and embedded in the surface of nanometer Si formed during annealing, at last, nanometer silicon with embedded structure is formed, which contributes to the blue emission.