Strong optical nonlinearity of CdS/nitrogen-doped reduced graphene oxide nanocomposites using Z-scan technique

CdS/nitrogen-doped reduced graphene oxide nanocomposites with different reduced graphene oxide contents were prepared using a hydrothermal method and characterized by XRD, FTIR, and SEM analyses. The successful formation of nanocomposites has been confirmed by X-ray powder diffraction and indicated that the average crystalline sizes decreased as the reduced graphene oxide contents increased. The SEM results approved the anchoring of CdS nanoparticles to nitrogen-doped graphene oxide surface. FTIR spectra confirmed the successful reduction of graphene oxide. CdS/nitrogen-doped reduced graphene oxide nanocomposites exhibited strong nonlinear absorption and refraction response under a nanosecond Nd:YAG laser at 532 nm which is due to the reversed saturable absorption and self-defocusing phenomena, respectively. Using the open-aperture Z-scan technique, the two-photon absorption coefficients, beta, of nanocomposites are calculated of the order of 10(-6) cm/W that is 10 times larger than beta of graphene oxide. The nonlinear refractive indices, n(2), for these nanocomposites are measured in the order of 10(-12) cm(2)/W with a negative sign. The results showed that the nonlinear optical response of CdS/nitrogen-doped graphene oxide nanocomposites is third-order and susceptibility, chi((3)), was calculated in the order of 10(-8) esu and increased by adding reduced graphene oxide to nanocomposites, which can be related to the variation in contents of sp(2) domains and sp(2) clusters in the CdS/nitrogen-doped reduced graphene oxide due to the various reduced graphene oxide levels. The results suggest that CdS/nitrogen-doped graphene oxide may be promising candidates for nonlinear optical applications.