Morphology related nonlinear optical response of tungsten trioxide nanostructures to nanosecond laser pulses

Nanomaterials continue to draw attention owing to their distinctive electronic, mechanical, and optical properties. Here, we synthesized one-dimensional nanowires (1DNWs), two-dimensional square nanoplates (2DSNPs), and three-dimensional nanoflower clusters (3DNFCs) tungsten trioxide (WO3) through a typical hydrothermal method. We confirm the morphologies of the nanostructures and propose a universal formation mechanism. The three WO3 nanostructures exhibit good crystallinities and thermal stabilities. We investigated the nonlinear optical (NLO) performance of the materials by the open-aperture Z-scan technique at a laser wavelength of 532 nm and a pulse width of 7 ns? Our WO3 nanostructures showed an irradiance intensity dependence transformation from saturable absorption to reverse-saturable absorption. Furthermore, the morphologies of the WO3 nanostructures were related to their NLO response. Among the three WO3 nanostructures we examined, the 1DNWs had the strongest NLO effect and the 3DNFCs had the weakest NLO activity. These results indicate that the NLO performances of WO3 nanostructures can be effectively optimized by morphological control. The observed NLO behaviors of the WO3 nanostructures are mainly attributable to nonlinear scattering and free carrier absorption. This study explores the potential for WO3 nanostructures to be applied as both saturable absorbers and optical limiters.