Journal of Ovonic Research Vol. 20, No. 3, May - June 2024, p. 325 - 331 Investigations on synthesis, growth and characterisations of a NLO material: L-Tryptophanium phosphite (LTP) P. D. H. B. Santhi a , R. S. Samuel a,b,* , R. Raja c , A. M. Hidayathullah a,d , S. Janarthanan e , P. Suresh f a Centre for Research and Evaluation, Bharathiar University, Coimbatore, India b Department of Physics, The New College, Chennai, India c Department of Physics, S.A. Engineering College, Chennai, India d Department of Physics, Aalim Muhammed Salegh College of Engineering, Chennai, India e Department of Physics, Adhi College of Engineering and Technology, Kancheepuram, India f Department of Physics, VSA Engineering College, Uthamasolapuram, Salem, India The nonlinear optical material L-Tryptophanium phosphite (LTP) was synthesised and grown by the process of slow evaporation solution growth. Characterisations like single crystal XRD, FT-IR, and H 1 NMR spectral measurements were done to find the crystal structure and functional groups. The crystal was found to possess good transparency for the whole visible region from the UV-Vis-NIR spectral analysis. The thermal behaviour like stability and breakdown of the crystal were assessed using TG-DTA analyses. The hardness of the crystal was determined using Vickers micro hardness study. The Kurtz- Perry approach was used to study the nonlinear optical (NLO) characteristics of the crystal. A good value of conversion efficiency in second harmonic generation (SHG) makes the generated crystal suitable for frequency conversion. (Received February 15, 2024; Accepted May 15, 2024) Keywords: Solution growth, Amino acid, XRD, FT-IR, NLO 1. Introduction Many researchers looking for innovative materials have been fascinated by the potential uses of crystal research, notably in the discipline of nonlinear optical (NLO) characteristics. The applications of NLO include optical communication, optical data storage, optical switching, and others [1, 2]. Moreover, NLO materials have been used as sensitive probes in environmental and biological sciences [3 – 5]. According to crystal engineering research, the alignment of donor- acceptor chromophores in noncentrosymmetric arrangement determines the formation of efficient second order nonlinear optical behaviour in the materials. The researchers have presented many practical ways in this respect [6–8]. Amino acids have carboxyl acid groups (COOH) which are proton-donors and amino groups (NH 2 ) which are proton-acceptors, making these materials for NLO applications. These are commonly employed because their chiral carbon atoms directly crystallize into non-centrosymmetric space groups and their zwitter ionic nature results in crystal toughness. An amino acid that occurs naturally, the L-tryptophan has no net charge and non-polar chain at physiological pH. The L-tryptophan shows non-exponential degradation of fluorescence in an aqueous solution. The observed decay could be attributed to the emission originating from the non-interconverting rotamers, that possess distinct lifetime as a result of varying rates of intermolecular charge transfer [9, 10]. Phosphonium salts are frequently transformed into ylides by the application of potent bases, however relatively weaker bases can also be employed provided that the salt exhibits sufficient acidity. Phosphonium salts, as photo-resistive materials, have potential applications in communication technologies [11]. This study focuses on the synthesis and * Corresponding author: sugarajsamuel@yahoo.com https://doi.org/10.15251/JOR.2024.203.325