[摘要]:The mechanism behind the visible-light absorption in N-doped titania is resolved through first-principles calculations of the formation energies and excitation energies of the relevant N-related defects in anatase and rutile TiO(2). The results indicate that substitutional N(O) is the source of the visible-light absorption through the photo-excitation of a localized electron from the N(O) to the extended conduction- band states.