Optical Materials 144 (2023) 114298 0925-3467/© 2023 Published by Elsevier B.V. Research Article Evaluation of structural, morphological and optical properties of Co 3 O 4 / SnO 2 nano-composite flms N.H.S. Nasralla a , Sahar M. Mousa b, * , Gehan T. El-Bassyouni c , G.M. El Komy a a Electron Microscope and Thin Films Dept., Physics Research Division, National Research Centre, 33 El-Buhouth St., P.O. 12622, Dokki, Giza, Egypt b Inorganic Chemistry Dept., Advanced Materials Technology and Mineral Resources Research Institute, National Research Centre, 33 EL-Buhouth St., P.O., 12622, Dokki, Giza, Egypt c Refractories, Ceramics and Building Materials Dept., Advanced Materials Technology and Mineral Resources Research Institute, National Research Centre, 33 EL- BuhouthSt., P.O. 12622, Dokki, Giza, Egypt A R T I C L E INFO Keywords: Sol-gel Co 3 O 4 /SnO 2 Nano-composite flms Optical properties ABSTRACT Nano-composite flms of cobalt (II⋅III) oxide/tin (IV) oxide (Co 3 O 4 /SnO 2 ) to be applicable for optoelectronic applications were prepared via sol gel method with variable concentrations of the Co 3 O 4 in the range of 0–45 mol %. Structural analysis using x-ray diffraction (XRD)of the composite powder Co 3 O 4 /SnO 2 revealed that a poly- crystalline structure was formed, whereas the composite flms showed an amorphous behavior. Transmission electron microscope (TEM) was performed to investigate the polycrystalline structure of the prepared flms. The results obtained from optical measurements indicated that the absorption edge was shifted towards longer wavelengths upon increasing the Co 3 O 4 content from 0 to 35 mol %. Further increase of Co 3 O 4 , revealed that the cut off transmission spectra were shifted to higher energies. The refractive index of prepared flms increases from 1.61to1.892 along with increasing the Co 3 O 4 mole %. The Co 3 O 4 /SnO 2 content ratio can control the optical properties and energy band gap of the mixture consequently, the present study is an innovative, promising, and appreciating the Co 3 O 4 /SnO 2 based composite for optical applications. 1. Introduction Nanostructure transition metal oxides such as Co 3 O 4 , vanadium oxide (V 2 O 5 ), manganese oxide (Mn 3 O 4 ), and chromium (III) oxide (Cr 2 O 3 )have involved extensive consideration because of their large optical properties [1]. Co 3 O 4 is p-type semiconductor while SnO 2 is n type semiconductor and a premium material reveals good transmittance in visible region with optical band gap 3.6 eV and. SnO2 also has cubic crystal structure and various morphologies. SnO 2 is applicable in lithium battery electrodes, catalysis and sensors, electrochemical storage. Tin oxide has recently got excellent scientifc interest due to its wide use [1]. In this perspective, the Co 3 O 4 /SnO 2 composite appears to have favorable semiconducting properties. Consequently, the combinations as n-p junctions are the foundation for most optoelectronic devices, and for the progress in nanoelectronics applications [2]. Oxide flms pre- pared via sol-gel method proved to be one of the best methods to obtain materials with nano-sized structure. The product of sol-gel method has many advantages as better homogeneity, higher purity and control of synthesis temperature [2–4]. Cobalt oxide is the most considered transition metal (TM) oxides; because of its signifcance for different scientifc technologies [5,6]. It takes place in two different oxidation states; CoO and Co 3 O 4 through a cubic lattice structure. Co 3 O 4 has an energy gap of 1.4–1.8 (eV) whereas for CoOit is 2.2–2.8 (eV) [7,8]. Co 3 O 4 demonstrates great potential applications as an excellent oxide for lithium-ion batteries, super capacitors, and catalysts [9]. These oxides are typically non-stoichiometric with an excess of ox- ygen that yields a p-type semiconducting behavior. In addition, the Co 3 O 4 has several industrialized applications, for instance catalyst in the hydro cracking route of crude fuels, solar selective absorber, colorant for glasses and ceramics and catalyst for oxygen progression [10]. Likewise, it is used as electro chromic materials, and newly invented application in super capacitors [11]. Few researchers have studied the p-n hetero- junction of Co 3 O 4 /SnO 2 in the feld of gas sensing and solar energy [12, 13] so, our research focus on synthesis of Co 3 O 4 /SnO 2, nanocomposite thin flms through the sol-gel dip coating technique and the study of the effect of varying the Co 3 O 4 concentration within the range 0–45 mol % aiming to tune their optical properties for optical devices and lenses applications. * Corresponding author. E-mail address: saharmousa69@yahoo.com (S.M. Mousa). Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2023.114298 Received 12 June 2023; Received in revised form 20 August 2023; Accepted 24 August 2023