Optik 125 (2014) 5069–5074 Contents lists available at ScienceDirect Optik jo ur nal homepage: www.elsevier.de/ijleo Effect of Co 2+ on the growth, optical properties and laser damage threshold of potential nonlinear optical l-alanine single crystal M. Lydia Caroline a,∗ , G. Mani a , S. Usha b a PG & Research Department of Physics, Arignar Anna Govt. Arts College, Cheyyar 604 407, Tamil Nadu, India b Bharath University, Selaiyur, Chennai 600 073, India a r t i c l e i n f o Article history: Received 6 October 2013 Accepted 10 April 2014 PACS: 42.70.Mp 81.10.Dn 61.05.Cp 81.70.Pg Keywords: Nonlinear optical material Growth from solutions X-ray diffraction Thermal analysis Optical properties a b s t r a c t Good transparent bulk single crystals of pure l-alanine (LA) and cobalt doped LA crystals have been syn- thesized and successfully grown by slow-cooling method from their aqueous solutions. The concentration of metal dopants in the mother solution with 0.5 mol% for cobalt was carried out individually and crystals were obtained with well defined morphology. The as grown metal doped and pure single crystals were characterized by single crystal XRD studies which confirm that the incorporation of metallic dopants has not changed the basic structure of the parent crystal. The absorption of these crystals was analyzed and the result confirms that they possess low absorption in the range 230–1100 nm. Fourier transform infrared (FTIR) spectroscopy was carried out to investigate the molecular vibrations of these crystals and to confirm the incorporation of the dopants. The thermal properties have been studied by TGA/DTA curves. The EDAX measurement and surface morphology were studied for pure and metal doped LA crys- tals. The second harmonic generation (SHG) signals were observed using Nd: YAG laser with fundamental wavelength of 1064 nm in pure and metal doped crystals. The laser damage threshold was measured for pure and metal doped LA crystals and also tested by using a Q-switched Nd: YAG laser showed enhanced LDT value for metal (Co 2+ ) doped LA crystal compared to pure LA crystal due to the metallic substitutions thus proving their useful candidature for nonlinear optical applications. © 2014 Elsevier GmbH. All rights reserved. 1. Introduction Amino acid family has over the years been subjected to exten- sive investigations due to their non-linear optical properties for their possible applications in various fields like telecommunication, optical computing, optical data storage and optical information processing. Complexes of amino acids with inorganic salts exhibit the advantage of the organic amino acids and the inorganic salts. The generation of coherent blue light through second harmonic generation (SHG) from near infrared (NIR) laser sources is an impor- tant technological problem that has attracted much attention in the last few years. Potential applications lie in the fields of high- density data storage, high-resolution printing and spectroscopy [1–3]. Organic crystals have large nonlinear susceptibilities com- pared to inorganic crystals. Among organic crystals for nonlinear optics (NLO) applications, amino acids display specific features ∗ Corresponding author. Tel.: +91 04182 225313/44 22281622; fax: +91 04182 222286; mobile: +91 9841720216/9443099026. E-mail addresses: lydiacaroline2006@yahoo.co.in (M. Lydia Caroline), mani0709@yahoo.com (G. Mani). of interest, such as (i) molecular chirality, which secures acen- tric crystallographic structures; (ii) absence of strongly conjugated bonds, leading to wide transparency ranges in the visible and UV spectral regions; (iii) zwitterionic nature of the molecule, which favors crystal hardness [4]. Further to that, -aminoacids can be used (iv) as chiral auxiliaries for nitro-aromatics and other donor- acceptor molecules with large hyperpolarizabilities [5] and (v) as a basis for synthesizing organic-inorganic compounds like l-arginine phosphate and derivatives [6]. l-Alanine (LA) is the smallest, natu- rally occurring chiral amino acid with a non-reactive hydrophobic methyl group ( CH 3 ) as a side chain. LA has the zwitterionic form ( + NH 3 -C 2 H 4 -COO - ) both in crystal and in aqueous solution over a large range of pH. The crystalline state is well defined structurally and can be successfully used for a detailed examination of a broad range of molecular properties. l-Alanine (LA) is the smallest, natu- rally occurring chiral amino acid with a non-reactive hydrophobic methyl group ( CH 3 ) as a side chain. l-Alanine (CH 3 CHNH 2 COOH), the simplest acentric member of the family, was first crystallized by Bernal [7] and later by Simpson et al. [8] and Destro et al. [9], who refined the structure (a = 6.032 ˚ A, b = 12.343 ˚ A, c = 5.784 ˚ A, ˛ = ˇ =  = 90 ◦ ) and assigned it the P2 1 2 1 2 1 space group. The growth and characterization of l-alanine crystals were reported by many http://dx.doi.org/10.1016/j.ijleo.2014.06.055 0030-4026/© 2014 Elsevier GmbH. All rights reserved.