Vol.:(0123456789) 1 3 J Mater Sci: Mater Electron DOI 10.1007/s10854-017-8177-7 Strong optical nonlinearity of CdS/nitrogen-doped reduced graphene oxide nanocomposites using Z-scan technique Fahimeh Abrinaei 1  · Salimeh Kimiagar 2  · Sepideh Gharedaghi 3   Received: 19 August 2017 / Accepted: 31 October 2017 © Springer Science+Business Media, LLC 2017 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. 1 Introduction Today, scientists around the world are looking for new mate- rials that have high performance in optoelectronics applica- tions. Nonlinear optics applications in improving the perfor- mance of optoelectronics devices are not covered, anybody. Despite the many materials that have been introduced for nonlinear optical applications, the difculty of the produc- tion process, the high price of raw materials, toxicity, and the difculty in using these materials in the systems are some restrictions that confront the progressing in optoelectronics with many problems. Among the important substances that have a high poten- tial in optoelectronic are semiconductors. Cadmium sulfde (CdS) and its composites are considered as functional semi- conductors that have shown good nonlinearity in various wavelengths [1–6]. Doping of graphene with nitrogen has been accepted as a simple and efective way to improve its electron structure [7, 8]. The large surface area and tunable surface properties of graphene make it suitable for the heterogeneous growth of favorable active guest materials. For this purpose, the surface functional groups such as hydroxyl, carbonyl, epox- ide and carboxyl groups on graphene surface can operate as appropriate nucleation sites for guest materials [9]. The introducing of nitrogen into the graphene structure makes it possible to enhance the Fermi level towards the conduc- tion band compared to pristine graphene [10]. In this case, Abstract 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 suc- cessful formation of nanocomposites has been confrmed by X-ray powder difraction and indicated that the average crystalline sizes decreased as the reduced graphene oxide contents increased. The SEM results approved the anchor- ing of CdS nanoparticles to nitrogen-doped graphene oxide surface. FTIR spectra confrmed 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 absorp- tion and self-defocusing phenomena, respectively. Using the open-aperture Z-scan technique, the two-photon absorption coefcients, β, of nanocomposites are calculated of the order of 10 −6 cm/W that is 10 times larger than β of graphene oxide. The nonlinear refractive indices, n 2 , for these nano- composites 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 nanocom- posites is third-order and susceptibility, χ (3) , was calculated in the order of 10 −8 esu and increased by adding reduced graphene oxide to nanocomposites, which can be related to * Salimeh Kimiagar s_kimiagar@iauctb.ac.ir 1 Department of physics, East Tehran Branch, Islamic Azad University, Tehran, Iran 2 Nano Research Lab (NRL), Department of Physics, Central Tehran Branch, Islamic Azad University, Tehran, Iran 3 Department of physics, Central Tehran Branch, Islamic Azad University, Tehran, Iran