Optical Materials 109 (2020) 110366 Available online 15 September 2020 0925-3467/© 2020 Elsevier B.V. All rights reserved. Broadband optical power limiting with the decoration of TiO 2 nanoparticles on graphene oxide Bala Murali Krishna Mariserla a, ** , K. Shadak Alee b , S. Kasthuri c , Pratiksha Gawas c , D. Narayana Rao d , Venkatramaiah Nutalapati c, * a Ultrafast Physics Group, Department of Physics, Indian Institute of Technology, Jodhpur, 342037, India b School of Physics, Indian Institute of Science Education and Research (IISER), Thiruvananthapuram, 695551, India c Department of Chemistry, SRM Institute of Science and Technology (SRMIST), Kattankulathur, 603203, India d School of Physics, University of Hyderabad, Hyderabad, Telangana, 500046, India A R T I C L E INFO Keywords: Two-photon absorption Reverse saturable absorption Optical limiting NLO Fluorescence quenching ABSTRACT Graphene, in its pristine form and analogs, is revolutionizing the architecture and designing of materials for high- performance optoelectronic devices. The functionalization of graphene is very attractive and emerging field of interest for nonlinear optical devices. In this work, we have synthesized Graphene oxide (GO) decorated with TiO 2 semiconducting nanoparticles for nonlinear photonic devices. The nonlinear optical (NLO) measurements of GO-TiO 2 composite were studied with a popular Z-scan technique for optical power limiting applications. Functionalized graphene oxide with TiO 2 nanoparticles exhibits a strong enhancement in optical-response with nanosecond laser pulses. The composite show fingerprints of reverse saturable absorption (RSA) dominated by two-photon absorption (TPA) along with enhanced nonlinear absorption due to transfer of electrons/energy between TiO 2 nanoparticles and graphene oxide. The systematic spectroscopic studies with TEM, XRD, FT-IR, micro-Raman, steady-state and time-resolved photoluminescence reveals that successful conjugation of GO and TiO 2 nanoparticles and probes the structural and optical properties. The nonlinear optical measurements demonstrate that GO-TiO 2 composite exhibits promising optical power limiting features than individual coun- terparts implicating the potential contingent towards broadband optical limiting applications. 1. Introduction Graphene and its analogs have attracted immense interest from the scientific and industrial community to the forefront of technological advances. Thanks to their exceptional properties such as high thermal- conductivity (~5000 W m  1 K  1 ), sizeable surface-volume ratio (2630 m 2 g -1 ), exceptional charge carrier mobility (200,000 cm 2 V  1 s  1 ) and the strong mechanical stability [1–4]. Graphene shows excellent optical transparency, and its functionalization can alter the bandgap associated with this transparency with other materials. Recently, it was shown that the linear dispersion of graphene exhibits strong optical responses in the nonlinear regimes at terahertz (THz) frequencies due to inter-band op- tical transitions [5]. These factors have made graphene and its analogs as ideal candidates for different optoelectronic applications [6]. The highly hydrophilic nature of graphene oxide (GO) due to oxygen- containing bonds is suitable for functionalization with push-pull type organic chromophores and other metal nanoparticles. Recent works on the functionalization of graphene with different conjugated organic chromophores, nanoparticles reveals that functionalized graphene exhibit strong NLO and optical limiting (OL) properties are found to be significantly enhanced in comparison to its precursor materials due to high order crystallinity and conjugation [7–10]. Our research group is actively involved in the design and development of graphene-based functional materials aimed at enhanced optical limiting behavior. Our recent results on the NLO behavior of graphene-porphyrin composites at different pulse regimes show diverse nonlinear optical responses. Strong excited state absorption (ESA) and enhanced two-photon absorption (TPA) that facilitate large reverse saturable absorption (RSA) in the nanosecond pulse regime. Contrast NLO response of saturable absorp- tion (SA) behavior exhibited in the femtosecond regime [11,12]. It was observed that charge-separated excited states are produced by photo-excited electron transfer is the critical factor for the enhanced * Corresponding author. ** Corresponding author. E-mail addresses: baluuoh@gmail.com, bmkrishna@iitj.ac.in (B.M. Krishna Mariserla), nvenkat83@gmail.com (V. Nutalapati). Contents lists available at ScienceDirect Optical Materials journal homepage: http://www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2020.110366 Received 21 April 2020; Received in revised form 13 August 2020; Accepted 22 August 2020