Growth and characterization of glycine picrate—Remarkable second- harmonic generation in centrosymmetric crystal Mohd. Shakir, S.K. Kushwaha, K.K. Maurya, Manju Arora, G. Bhagavannarayana à Materials Characterization Division, National Physical Laboratory, New Delhi 110 012, India article info Article history: Received 2 May 2009 Received in revised form 25 May 2009 Accepted 2 June 2009 Communicated by M. Schieber Available online 10 June 2009 PACS: 61.05.C 61.72.-y 77.84.-s 42.70.Mp Keywords: A1. High-resolution X-ray diffraction A2. Single crystal growth B2. Dielectric materials B2. Nonlinear optic materials abstract Remarkable second-harmonic generation (SHG) efficiency has been observed in the glycine picrate (GP) though it crystallizes in centrosymmetric structure. Bulk single crystals of GP with a good size of 20  10  3 mm 3 have been successfully grown by the slow cooling method in aqueous medium. Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) and FT-Raman studies have confirmed, respectively, the crystal structure and functional groups of the grown crystal. Crystalline perfection of single crystals has been evaluated by high-resolution X-ray diffractometry (HRXRD) using a multicrystal X-ray diffractometer and found that the grown crystals are nearly perfect. Nonlinear optical (NLO) behavior of glycine picrate crystals has been studied for the first time by Kurtz powder technique and its second-harmonic generation efficiency is found to be 2.34 times higher than that of KDP. Transparency of crystals in UV–vis–NIR region has also been studied. Dielectric measurements have been carried out using an impedance analyzer over a wide range of frequency (100 Hz–3 MHz) at room temperature. The slight decrease in dielectric constant has been observed as the frequency is increased and the dielectric loss is very low for the entire frequency range. The ac conductivity is almost constant up to 1 MHz and sudden increase has been observed above this frequency. & 2009 Elsevier B.V. All rights reserved. 1. Introduction In the recent past two decades, nonlinear optical (NLO) crystals have attracted the scientists and technologists due to their potential applications in the area of photonics including optical information processing [1–4], high-energy lasers for inertial confinement fusion research [5], color display, electro-optic switches, frequency conversion, etc. [6]. The organic compounds exhibit larger NLO response than inorganic materials due to the presence of active p-bonds. However, these materials have poor mechanical strength, thermal stability, laser damage threshold, etc. As organic materials exhibit prominent NLO properties, it is very important to synthesize new organic NLO materials. Picric acid is having tendency to form the stable picrate compounds with various organic molecules like glycine due to the presence of active p- and ionic bonds [7]. It is almost a well proven fact by both theory and experiment that for having a good second- harmonic generation (SHG) character, the material should have a non-centrosymmetric crystalline structure. However, a very few reports are available in the literature which show that the centrosymmetric crystals [8–10] or films [11] also exhibit NLO properties. Glycine picrate (GP) is a stable organic compound of picric acid and glycine with monoclinic crystal system having lattice parameters a ¼ 14.968, b ¼ 6.722 and c ¼ 15.165 ˚ A and space group P2 1 /a [12,13]. Recently, single crystals of GP were grown by simultaneous slow evaporation and cooling technique and characterized [13]. However, crystalline perfection, SHG efficiency and dielectric studies have not been carried out so far. In the present investigation, GP has been synthesized and its single crystals have been grown by slow cooling method [14]. The powdered specimen of crystals was subjected to powder X-ray diffraction (PXRD) to calculate the lattice parameters and confirm the crystalline structure. To analyze the vibrational modes present in crystals, these were subjected to Fourier transform infrared (FT- IR) and FT-Raman spectrometer in the wave-number range 400–4000 cm 1 with 4 cm 1 resolution at ambient temperature. High-resolution X-ray diffractometry (HRXRD) has been employed on the as-grown single crystal to assess its crystalline perfection. An impedance analyzer has been used to study the dielectric properties of GP over a wide frequency range from 100Hz to 3 MHz at room temperature. Homogeneous powdered specimen of GP was characterized by Kurtz powder technique to evaluate SHG efficiency of grown crystals. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2009.06.007 à Correspondence to: Crystal Growth and Crystallography Section, National Physical Laboratory, New Delhi 110 012, India. Tel.: +911145608261; fax: +911125726938/52. E-mail address: bhagavan@mail.nplindia.ernet.in (G. Bhagavannarayana). Journal of Crystal Growth 311 (2009) 3871–3875