Cryst. Res. Technol. 42, No. 11, 1097 – 1103 (2007) / DOI 10.1002/crat.200710954 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Investigations on the growth, optical behaviour and factor group of an NLO crystal: L-alanine alaninium nitrate A. Aravindan 1,2 , P. Srinivasan 1 , N. Vijayan 3 , R. Gopalakrishnan* 1 , and P. Ramasamy 4 1 Department of Physics, Anna University, Chennai – 600 025, India 2 Department of Physics, Sri Venkateswara College of Engineering, Pennalur, Sriperumbudur, 602105, India 3 Materials Characterization Division, National Physical Laboratory, New Delhi- 110 012, India 4 SSN College of Engineering, Kalavakkam- 603 110, India Received 11 April 2007, revised 14 May 2007, accepted 1 June 2007 Published online 6 August 2007 Key words organic compounds, growth from solutions, X-ray diffraction, nonlinear optic materials. PACS 81.10.-h Amino acid family crystals exhibit excellent nonlinear and electro-optical properties. L-alanine alaninium nitrate (LAAN) single crystal belonging to the amino acid group was grown by slow cooling solution growth technique. The High resolution X-ray diffraction (HRXRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, UV-Vis., Photoluminescence (PL) and Factor group analyses were carried out. The factor group analysis reveals 183 internal vibrations for the title compound. The second harmonic generation property was tested by Kurtz-Perry powder technique. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction The overwhelming success of molecular engineering in controlling nonlinear optical (NLO) properties has attracted the attention of researchers to search for a variety of new types of non-linear optical materials [1]. An organic molecule should have high second-order hyperpolarizability (β) to exhibit effective nonlinear optical properties [2]. Organic molecules containing π electron systems asymmetrized by the electron donor and acceptor groups are highly polarizable entities for NLO applications. The donor / acceptor benzene derivatives can produce high molecular nonlinearity. Nonlinear optical (NLO) materials, which can generate highly efficient second harmonic blue-violet are of great interest for various applications including high speed optical communication, wireless optical computing, optical parallel information processing, optical disk data storage, laser fusion reactions, laser remote sensing, color display, medical diagnostics, etc. [3-5]. Organic compounds exhibit high nonlinear optical response, in many cases, orders of magnitude larger than the widely known inorganic materials. Alanine is an efficient organic NLO compound under amino acid category. The title compound was first crystallized by Manuela Ramos Silva [6], which belongs to the monoclinic crystal system with space group P2 1 and the molecular weight is 241.21. The L-alanine alaninium nitrate (LAAN) is the charge transfer complex of L-alanine and nitric acid. The intra-molecular charge transfer substantially modified by the electron-vibration interactions is the principal role in such kind of systems. That is the main reason why investigations of the corresponding FTIR spectra are very crucial for understanding the nonlinear optical properties [7]. The SHG efficiency of L-alanine is about one third of KDP but for the title compound LAAN is many orders of magnitude higher than that of KDP due to the protonation of the amino group. In this investigation, we report for the first time, the bulk growth and characterization studies of LAAN single crystals. The solubility of LAAN was estimated at different temperatures using water as a solvent. The grown single crystals were characterized by various characterization methods. The NLO response was tested by Kurtz-Perry powder technique using an Nd:YAG laser. ____________________ * Corresponding author: e-mail: krgkrishnan@annauniv.edu, krgkrishnan@yahoo.com