Strain influence on the structural properties of nitrogen and fluorine codoped TiO2

The present work aims at outlining the role of lattice strain in modifying the structural properties of doped samples. Dual doping of TiO2 by anions nitrogen (N) and fluorine (F) was carried out by a typical hydrothermal route using inorganic precursors; ammonia solution (NH3-H2O) and ammonium fluoride (NH4F). N monodoped TiO2 (NT) showed poor crystallinity while codoping with N, F promoted the crystal growth thereby resulting in tunable particle sizes. The synergistic effects of codoping was systematically examined by changing the molar ratio of F and N. The crystalline development in the doped samples was investigated by X-ray broadening and Williamson-Hall (W-H) analysis was used to study the contribution of lattice strain to it. In comparison to NT, codoped samples showed better visible light sensitivity. Strain; even in minute amounts; induced a pronounced effect on the structural properties of the doped samples. NFT1 with the maximum strain value exhibited distinct hexagonal morphology in comparison to NFT2 and NT with lower strain values. Also, photoluminescence intensity got enhanced with increase in strain values. This study manifests the influence of strain on the dynamics of charge carriers which might affect photoactivity as well.