First-principles calculation of the band structure, electronic states, and optical properties of Cr-doped ZnS double-wall nanotubes

Abstract

The density functional theory (DFT) and generalized gradient approximation plus U (GGA+U) are adopted to investigate the effects of chromium (Cr) doping on the band structure, density of states (DOS), dielectric functions, and optical absorption of (4,4)@(m,m) (m=6, 7, 8) double-wall zinc sulfide nanotubes (DW-ZnSNTs). Cr doping is found to produce half-metallic features in the DW-ZnSNTs and the band gaps of the minority spin are expanded for (4,4)@(6,6) DW-ZnSNTs, while they are reduced for (4,4)@(7,7) and (4,4)@(8,8) DW-ZnSNTs. When Cr is doped in the double-wall nanotubes, both the static dielectric constants and static refractive index are increased, but the maximum values of the real and imaginary parts of the dielectric functions, the maximum extinction coefficients, the maximum refractive index and extinction coefficient are decreased slightly. Compared to the pristine ones, the absorption peaks of Cr doped (4,4)@(m,m) DW-ZnSNTs are reduced a little and new peaks appear in the ultraviolet region. If the separation between adjacent walls is increased, light absorption is enhanced but the effects of Cr doping decrease due to the reduced interactions between the inner and outer nanotubes. The results illustrate that the electronic and optical properties of ZnS nanotubes can be improved by metal doping, which is expected to expedite the use of the materials in applications, such as, ultraviolet light-emitting diodes, flat panel displays, and photocatalysis.