Abstract: Using the first-principles density functional theory , band structures , electronic density of states and optical properties of Sm-doped , C-doped , and Sm-C co-doped SnO 2 systems were calculated .The results show that the Sm-C co-doped SnO 2 structure in which Sm and C are the nearest neighbors is more stable than that of the next-nearest.The energy gap of the co-doped system is minimum , as demonstrates that the energy which made the electrons excite from valence band into the conduction band is the least . the optical absorption edge of the doped systems appeared shifted towards the longer wavelength side , and the degree of the shifting of Sm-C co-doped system is very big , which states that the doping led to expand the range of responding to visible light .The reflection coefficient , static dielectric constant , and static refractive index of doped systems are all bigger than those of pure SnO 2 , especially the optical values of Sm-C co-doped system is the greatest .

Key words: Using the first-principles density functional theory , band structures , electronic density of states and optical properties of Sm-doped , C-doped , and Sm-C co-doped SnO 2 systems were calculated .The results show that the Sm-C co-doped SnO 2 structure in which Sm and C are the nearest neighbors is more stable than that of the next-nearest.The energy gap of the co-doped system is minimum , as demonstrates that the energy which made the electrons excite from valence band into the conduction band is the least . the optical absorption edge of the doped systems appeared shifted towards the longer wavelength side , and the degree of the shifting of Sm-C co-doped system is very big , which states that the doping led to expand the range of responding to visible light .The reflection coefficient , static dielectric constant , and static refractive index of doped systems are all bigger than those of pure SnO 2 , especially the optical values of Sm-C co-doped system is the greatest .