High nonlinear optical response of Lanthanum-doped TiO2 nanorod arrays under pulsed laser irradiation at 532 nm

Abstract

La-doped TiO2 nanorod arrays were prepared using the hydrothermal method and the effects of doping on the structural and linear optical properties were considered by using UV–Vis diffused reflectance spectroscopy (DRS), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analyses. The XPS analysis confirmed the presence of La doping in TiO2 nanorod arrays. According to XRD patterns, La doping leads to an enhancement of lattice parameter, c, as well as a reduction in the other lattice parameter, a, which indicates an expansion along the c direction of the lattice in La-doped TiO2 nanorods. From UV–Vis DRS analysis, the band gap energy of undoped and doped samples were calculated by using Kubelka- Munk method that exhibited a slight decreasing with adding of La doping. The measurements of nonlinear optical (NLO) properties of undoped and La-doped TiO2 nanorod arrays carried out using a nanosecond Nd: YAG pulse laser by using the Z-scan technique. Both samples showed a negative NLO refractive index at 532 nm. The NLO absorption of undoped and La-doped nanorod arrays is attributed to two-photon absorption. The nonlinear susceptibility, χ(3), of undoped and La-doped TiO2 nanorods was determined by the Z-scan technique of the order of 10−5 esu which is remarkably large value. The consequences suggest that undoped and La-doped TiO2 nanorod arrays may be a promising candidate for the NLO applications.