DFT insights into the electronic and optical properties of fluorine-doped monoclinic niobium pentoxide (B-Nb sub(2)O sub(5):F)

We report on the effect of fluorine doping on the electronic structure and optical properties of monoclinic niobium pentoxide (B-Nb sub(2)O sub(5)) as revealed by the first principles calculations. Density functional theory (DFT) along with generalized gradient approximation (GGA) at the revised Perdew-Burke-Ernzerhof (PBEsol) exchange-correlation functional was used in this study. The band calculations revealed that the studied materials are indirect bandgap semiconductors, with bandgap energies of 2.67 and 2.28 eV for the undoped and F-doped B-Nb sub(2)O sub(5), respectively. Upon doping B-Nb sub(2)O sub(5), the Fermi level shifts towards the conduction band, allowing optical absorption in the visible region with enhanced transmittance in the wavelength range 400-1000 nm. The calculated static refractive index of the undoped B-Nb sub(2)O sub(5) is in good agreement with the reported experimental value, which is enhanced upon F-incorporation resulting in cladding properties for the F-doped B-Nb sub(2)O sub(5). Also, the effective mass of free charge carriers increased upon F-doping. The enhanced properties were attributed to the effect of the excessive valent electron of the incorporated F atom.