Blue luminescence at about 431nm is obtained from epitaxial silicon after sequential processing of C+ implantation, annealing in hydrogen ambience and chemical etching. With the increase of chemical etching, the blue peak was enhanced at first, decreased then and substituted by a red peak at last. C=O compounds induced during C+ implantation are embedded in the surface of nanometer Si formed during annealing, and nanometer silicon with embedded structure is formed at last, which contributes to the blue emission.