By means of first principles calculations we show that both rutile and anatase phases of bulk TiO2 doped by S, Se or Pb can display substantial decreasing in the band gap (up to 50%), while doping by Zr does not sizably affect the band-gap value. Moreover, the absorption edge is shifted (up to 1 eV) to the lower energy range in the case of TiO2 doped by S or Pb that opens a way to enhancin...