Mass ratio-dependently tunable enhancement of the optical nonlinearities of SnO2/RGO composites

Abstract

The composite of graphene and semiconductor nanoparticles has attracted increasing interest in the search for novel nonlinear optical materials. Herein, composites of reduced graphene oxide (RGO) and SnO2 nanoparticles with different mass ratios were synthesized via a facile hydrothermal method. The structural morphology and basic physical properties of the SnO2/RGO composites were characterized using TEM, SEM, XRD, Raman, XPS and UV–Vis spectra, indicating that SnO2 nanoparticles were uniformly anchored on the surface of graphene nanosheets through covalent and partial-ionic bonds. The third-order optical nonlinearities of the composites were studied for the first time by the Z-scan technique using a picosecond laser at 532 nm. It was found that the composites demonstrated saturable absorption and positive nonlinear refraction properties, and both were significantly enhanced compared with pure SnO2 nanoparticles and RGO nanosheets, and the enhancement was tunable with the variation of SnO2:GO mass ratio. The maximum saturable absorption coefficient and the third-order susceptibility of the as-prepared SnO2/RGO composites were obtained to be −2.93×10–11 m W−1 and 2.25 × 10–11 esu, respectively. The maximum saturable absorption modulation depth obtained was 10% with the corresponding saturation light intensity of 0.3 GW cm−2. Moreover, the optimised third-order susceptibility of SnO2/RGO was found much greater than many other materials ever studied. Several involved factors contributing to the nonlinearities were discussed. The results propose that the third-order optical nonlinearities of SnO2/RGO and other similarly structured composites can be potentially tuned to meet certain application requirements of nonlinear optical devices by controlling the mass ratio of semiconductor to graphene.