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Growth, structural, optical and thermal studies of semi‑organic nonlinear optical potassium hydrogen oxalate single crystal S. Devi1 · Deepa Jananakumar1 Received: 23 December 2019 / Accepted: 20 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Single crystals of semi-organic nonlinear optical material potassium hydrogen oxalate are grown from the aqueous solutions of potassium hydroxide and oxalic acid in 1:1 stoichiometric ratio by slow evaporation solution growth method at room temperature. The grown crystals are subjected to various characterization techniques to explore their structural explication, thermal, linear and nonlinear optical perspectives for optoelectronic device applications. The monoclinic structure with non-centrosymmetric space group P21/c of the titular compound has been confirmed by single-crystal X-ray diffraction. The crystal packing is ruled by extensive networks of hydrogen bonds revealed by the detailed study of the refinement of the crystal structure. Optical transparency of the crystal in the entire visible region has been confirmed by ultraviolet–visible-near infrared (UV–Vis-NIR) analysis. The robust thermal stability of the grown crystal is ensured by thermogravimetric–differential thermal analysis. The presence of expected functional groups in the grown crystal has been confirmed by Fourier transform infrared spectroscopic studies. Second-harmonic generation efficiency has been calculated by Kurtz powder method. Keywords  Growth from solutions · Inorganic compounds · Organic compounds · Nonlinear optical materials

1 Introduction In recent years, nonlinear optical (NLO) materials with high thermal stability have been studied extensively for their potential applications in optoelectronics, signal conversion, optical data storage, frequency conversion, optical second harmonic generation, optical switching and photonics [1, 2]. The crystals grown from organic compounds have a high degree of optical non-linearity than inorganic compounds, but they are thermally and mechanically less stable [3]. In addition, organic materials cannot be grown to larger size with better quality single crystals for device applications. In contrast, NLO materials from inorganic compounds have outstanding mechanical and thermal properties, but they retain relatively limited nonlinearity [4, 5]. Thus, the intrinsic limitations on the optimized nonlinearity in inorganic materials and the restrained successes in growing the device grade single crystals of organic materials have led to researchers to search on * S. Devi [email protected] 1



Department of Physics, Velalar College of Engineering and Technology, Erode 638012, India

alternative approaches. By combining organic molecules of high polarizability with thermally stable and mechanically robust inorganic compounds, a new class of material called semi-organic is formed with high nonlinear optical properties and excellent thermal and mechanical properties [6–11]. Oxalic acid is a good crystalline organic acid having