Nonlinear optical properties of hydroxyl groups modified multi-walled carbon nanotubes

► Systematic research on nonlinear optics properties of carbon nanotubes should be necessary to obtain the optimal experimental configuration in application. In this work, we comprehensively studied the nonlinear optics properties of hydroxyl groups modified MWNTs (MWNTs-OH) with diameter of 20-30 nm (MWNTs2030-OH) dispersed in water, N,N-dimethylformamide (DMF) and chloroform. Nonlinear optical properties of MWNTs-OH with different diameter in DMF were also studied, compared with multi-walled carbon nanotubes in DMF and C60 in toluene. Parts of interesting results are summarized as follows. ► Solvent effect and pulse-width effect on the nonlinear optics properties of MWNTs2030-OH were observed. This indicates the nonlinear scattering is dominant, unlike some soluble carbon nanotubes for which nonlinear absorption mechanism is proposed by people. ► For the DMF dispersion, the concentration which exceeds to a certain level can lead to the saturation of optical limiting performance. Therefore, it is required to choose suitable mass concentration for a certain laser source. ► The attachment of hydroxyl groups does not significantly influence the nonlinear optics properties of MWNTs2030-OH but produce better dispersion in DMF. ► The diameter has no significant influences on the nonlinear optics properties of MWNTs-OH and MWNTs-OH with different diameters in DMF dispersion shows stronger nonlinear optics properties than C60 at the higher fluence due to nonlinear scattering.