Growth and characterization of nonlinear optical single crystal: Glycine zinc sulfate

Transcription

1 International Journal of ChemTech Research CODEN (USA): IJCRGG ISSN : Vol.6, No.5, pp , Aug-Sept 2014 Growth and characterization of nonlinear optical single crystal: Glycine zinc sulfate M. Lenin*, M. Chandrasekar, G. Udhayakumar Department of Physics, T.A.G. Govt. Arts College Tindivanam , India *Corres. author: lenincgc@gmail.com Telephone No : Abstract: Single crystal of Glycine zinc sulfate (GZS), a semiorganic nonlinear optical (NLO) material, have been grown by Sankaranarayanan-Ramasamy (SR) method from a mixture of aqueous solution of glycine and zinc sulfate at ambient temperature. Good optical quality single crystals with dimensions up to 45 length x 15 diameter are obtained. The grown crystal was subjected to powder X-ray diffraction studies, High resolution X- ray diffraction, the thermal analysis, FTIR and UV-visible spectral analysis have been carried out. The UV cutoff of GZS is below 300 nm and has a wide transparency window, which can be suitable for second harmonic generation of laser in the blue region. Nonlinear optical characteristics of GZS were studied using Q-switched Nd:YAG laser (λ=1064 nm). The second harmonic generation conversion efficiency of GZS is comparable with potassium dihydrogen phosphate. Keywords: X-ray diffraction, Growth from solutions, Single crystal growth, Nonlinear optical materials. 1. Introduction It is generally believed that organic-inorganic nonlinear optical crystal material compound not only possesses the high optical nonlinearity of a purely organic compound but also the favorable thermal and mechanical properties of an inorganic compound. They do not have π electrons as organic NLO materials [1]. Amino acid family crystals have over the years been subjected to extensive investigations by several researchers for their non-linear optical (NLO) properties [2 4]. In the recent years, efforts have been made on the growth of amino acid mixed organic inorganic complex crystals, in order to improve the chemical stability, laser damage threshold, and linear and non-linear optical properties. The growth and study on a series of semi-organic compounds such as L-arginine phosphate (LAP) [5], L-arginine hydrobromide (LAHBr) [6], L-arginine hydrochloride (LAHCl) [7], L-histidine dihydrogen phosphate (LHP) [8], L-histidine tetrafluoroborate (L-HFB) [9], and L-arginine tetrafluoroborate (L-AFB) [10] have been reported. Among the amino acids, glycine [amino acetic acid: NH 2 CH 2 COOH] is the simplest amino acid. It has been reported that glycine combines with H 2 SO 4 [11], AgNO 3 [12], CaCl 2 [13], CaNO 3 [14], BaCl 2 [15], CoBr 2 [16], NaNO 3 [17], HCl [18] etc., to form single crystals. But only very few of these are reported to have nonlinear optical (NLO) property such as glycine sodium nitrate, bisglycine hydrogen chloride, etc. Hence, glycine mixed semi-organic material will be of special interest as a fundamental building block to develop many complex crystals with improved NLO properties. In view of this, the present investigation has been focused on the growth of semi-organic glycine zincsulfate (GZS) single crystals. The optical properties and thermal properties of GZS single crystals have been studied.

2 M. Lenin et al /Int.J. ChemTech Res.2014,6(5),pp Material Synthesis GZS was synthesized from equimolar ratio of glycine (grade AR) and zincsulfate (grade AR), (1:1 molar ratio). Single crystals of GZS were grown by slow evaporation of the aqueous solution. The synthesized compound was stirred at 60 C for 1 hr to thoroughly dissolve in double distilled water and let to cool off to room temperature. Few drops of sulphuric acid were added while stirring to adjust the ph value to 3 2 at 32 C (room temperature) and the solution was filtered twice to remove the suspended impurities as well as the micro crystals. The saturated solution was kept at room temperature and subjected to slow evaporation. Good-quality single crystals of 14 x12 x10 mm 3 are obtained by solvent evaporation at room temperature shown in Fig. 1a. The grown crystals are stable at room temperature. The solution growth technique is widely employed to grow single crystals of semiorganic compounds. In order to select the suitable solvent for crystal growth, the solubility of GZS in different solvents such as water, acetone, methanol, and ethanol, were measured. The solubility curve of GZS in water was determined by using equilibrium method. The solubility of GZS was found to be higher in deionized water compared to other solvents (150g/100ml). From the solubility studies deionized water was found to be a better solvent for bulk single-crystal growth of GZS. The 2 mm thickness of GZS was prepared from conventional solution method which was used as a seed crystal for SR method. The SR method experimental setup to grow GZS was designed as earlier as reported [19,20]. It consists of two ring heaters, one at the bottom (around the seed crystal) and the other at the top (around the solution surface) that provide the necessary temperature difference. The top heater provides the necessary temperature for solvent evaporation of around 40 C while the bottom one is kept at room temperature. The later one was moved upwards depending on the growth rate of the crystal. Each of the heaters was connected to a temperature controller equipped with a thermocouple to set the desired temperature. In this condition, growth of highly transparent crystal was observed (Fig. 1b). The crystals of 45 mm length and 15 mm diameter have been grown in a period of 30 days. The average growth rate was about ~2 mm/day. The entire SR set-up was placed in a water bath in order to avoid thermal fluctuations. Fig 1 (a) The SEST grown crystal (b) SR grown GZS 3. Characterizations Single crystal x-ray diffraction was carried out to find out the unit cells of the grown crystal. Powder x- ray diffraction pattern was recorded using Kappa Apex-2 diffractrometer with CuKα (λ= Å) radiation for structural analysis. HRXRD studies were made to reveal the crystalline perfection. In order to confirm the presence of functional groups in the crystal lattice, FTIR spectra were recorded by KBr pellet technique using a Bruker Model IFS 66V spectrometer in the wavelength range cm -1 for GZS crystals. Optical transmission spectrum recorded using a UV visible spectrometer (SHIMADZU-1601) revealed the linear optical property of the GZS crystal. 4. Results and discussion 4.1 X-ray diffraction study The grown crystal was subjected to single crystal X-ray diffraction in order to find out the lattice parameter and the morphology of the crystal. It was found that the grown crystal crystallizes in orthorhombic system with space group Pca2 1 whose a = 8.43Å b =8.22Å, c = 12.37Å. The results show good agreement with the reported value [21]. The grown crystal was crushed to powder and X-ray powder diffraction studies have

3 M. Lenin et al /Int.J. ChemTech Res.2014,6(5),pp been carried out. The recorded spectrum is shown in Fig. 2. The PXRD peaks are indexed with the help of the DICVOL91 program Intensity (232) 5 0 (111) (112) (020) (120) (203) (124) (025) (241) (θ ) d eg Fig. 2. Powder x-ray diffraction spectrum of grown crystal 4.2 HRXRD studies Fig. 3 shows the high-resolution diffraction curve (DC) recorded for GZS specimen grown by slow evaporation technique using (111) diffracting planes in symmetrical Bragg geometry by employing the multicrystal x-ray diffractometer described above with MoKα 1 radiation. Diffracted X-ray intensity [c/sec] G ZS_SEST ( ) Planes M okα 1 (+,-,-,+) 68" 250" GZS_SR METHOD 35" G lancing angle [arc sec] Fig.3 HRXRD curve of SR grown crystal As seen in the figure, the curve does not contain a single diffraction peak. The solid line, which follows well with the experimental points (filled rectangles), is the convoluted curve of three peaks using the Lorentzian fit. The well resolved peak at 250 arc sec away from the main peak shows an internal structural low angle (tilt angle > 1 arc min but less than an arc degree) boundary [22] whose tilt angle (misorientation angle between the two crystalline regions on both sides of the structural grain boundary) is 250 arc sec from the main peak. The broad central deconvoluted (dotted) curve with very less peak intensity can not confirm a clear boundary but indicates some mosaicity throughout the crystal. The FWHM (full width at half maximum) of the main peak and the well resolved low angle boundary (having 250 arc sec tilt angle) are respectively 35 and 68 arc sec.

4 M. Lenin et al /Int.J. ChemTech Res.2014,6(5),pp Though the specimen contains a low angle boundary, the relatively low angular spread of around 400 arc sec of the diffraction curve and the low FWHM values show that the crystalline perfection is reasonably good. 4.3 Infrared (IR) studies The FT-IR spectrum was recorded in the frequency range of cm -1 to identify the functional groups in GZS and is shown in Fig. 4. The sample is made in pellet form using KBr. Fig. 4 FTIR spectrum of Glycine zincsulfate crystal The characteristic bands at 3500 cm -1 and 1476 cm -1 due to NH asymmetric stretching and COO - stretching [23] confirmed the existence of amino group. The band at 3028 cm -1 established the presence of CH group. The bands at 1651 cm -1 and 1433 cm -1 established the presence of NH 3+ and C = O symmetric stretching. The bands at 1115 cm -1 and 1037 cm -1 established the presence of C - C stretching. The band at 617 cm -1 is assigned to the COO - out of plane bending vibration. The vibration of CH 2 group appears at 1476 cm -1. The characteristic stretching vibrations of SO 4 - group appear at 894 and 648 cm -1. The carboxylate group (COO - ) asymmetric and symmetric stretching vibrations appear at 1651 and 1433 cm -1 [24]. The frequencies at 504, 892 and 1614 cm -1 are assigned to carboxylate group which are observed at , and 1618 cm -1, respectively. The presence of carboxylate ion and ammonium ion clearly indicated that glycine molecule exists in zwitter ionic form in GZS. 4.4 Optical properties The transmittance spectrum of a 2mm thickness glycine zinc sulfate crystal was recorded as a percentage of transmittance (T %) vs. wavelength. thickness 2mm was used. The GZS crystals are quite transparent almost till the UV region as the cutoff wavelength is around 220 nm, and show more than 70% transmittance and there is no absorption in the entire visible region. As there is no absorption in the visible and near infrared region it can be used as a potential material for frequency doubling. The SHG behavior of GZS crystal was observed by illuminating the crystal using spectra physics quanta ray GCR-2 Nd: YAG laser with the first harmonic output of 1064 nm, a pulse width of 8ns and pulse energy of up to 300 mj. The beam was well focused before it was incident on the crystal. The second harmonic signal generated in the crystal was confirmed from a strong bright green emission emerging from the GZS crystal which shows that the samples exhibit good NLO property. The second harmonic generation efficiency has been found to be comparable to phase matched potassium dihydrogen phosphate crystal. The output power of the crystal was measured using OPHIR power meter model DG with power head model OPHIR 30A. 4.5 Thermal Analysis TGA spectrum of GZS was obtained. A 4.2 mg sample was heated at a rate of 10K/min in inert nitrogen atmosphere. TGA curves show that there is a weight loss at 70 C which may be due to loss of moisture. The 14% weight loss is due to the removal of occluded and adsorbed water molecules occurring up to 85 C. The

5 M. Lenin et al /Int.J. ChemTech Res.2014,6(5),pp loss at 122 C may be due to dehydration of water molecules of crystallization occurring which is continued up to 125 C. There is no further weight loss up to 310 C and the sample undergoes gradual weight loss till 470 C. The loss in weight, in the temperature range C, suggest loss of CO. The compound weight gradually decreases as the temperature goes up to 630 C. It may be due to loss of CO 2. Fig. 5 TGA spectrum of grown crystal 5. Conclusion We have synthesized a new non-linear optical crystal Glycine zincsulfate by SR method. Seed crystal for SR method was obtained from slow evaporation technique. Optically good quality single crystals of GZS were grown using the said technique. The crystalline nature of the grown sample was confirmed by X-ray diffraction analysis. The crystal perfection was observed by HRXRD studies and showed that the crystalline perfection is good. Various functional groups present in the grown crystal were identified by FTIR spectrum. The crystal possesses good stability and does not show any hygroscopic and efflorescent effect for a long time. The thermal stability of the grown sample was studied by TGA. The TGA was used to formulate the dehydration patterns of the compound. The optical quality of the grown crystal was justified by optical transmission studies and showed that the UV cutoff wavelength of GZS is 220 nm. The second harmonic generation efficiency was measured and has been found to be comparable to phase matched potassium dihydrogen phosphate crystal. This new crystalline material possesses an effective second-order nonlinear optical susceptibility comparable with KDP, with the significant advantage of being stable at room temperature. References 1. V. Venkataramanan, J.N. Sherwood and H.L. Bhat, Proc. SPIE Vol (2002). 2. L. Misoguti, A.T. Varela, F.D. Nunes, V.S. Bagnato, F.E.A. Melo, J. Mendes Filho, S.C Zilio, Opt. Mater. 6 (1996) W.S. Wang, M.D. Aggarwal, J. Choi, T. Gebre, A.D. Shields, B.G. Penn, D.O. Frazier, J. Cryst.Growth 198 (1999) S. Chenthamarai, D. Jayaraman, P.M. Ushasree, K. Meera, C. Subramanian, P. Ramasamy, Mater. Chem. Phys. 64 (2000) D. Eimerl, S. Velsko, L. Davis, F. Wang, G. Loicono, G. Kennedy, IEEE J. Quantum Electron. QE-25 (1989) S.B. Monaco, L.E. Davis, S.P. Velsko, F.T. Wang, D. Eimerl, J. Cryst. Growth 85 (1987) L.N. Rashkovich, B.Yu. Shekunov, J. Cryst. Growth, 112 (1991) E. Espinosa, B. Wyncke, F. Brehat, X. Gerbaux, S. Veintemillas, E. Molins, Infrared Phys. Technol. 38 (1997) M.D. Aggarwal, J. Choi, W.S. Wang, K. Bhat, R.B. Lal, A.D. Shields, B.G. Penn, D.O. Frazier, J. Cryst. Growth 204 (1999) C. Owens, K. Bhat, W.S. Wang, A. Tan, M.D. Aggarwal, B.G. Penn, D.O. Frazier, J. Cryst. Growth 225 (2001) B. Brezina, Mat. Res. Bull. 6 (1971) J.K. Mohan Rao, M.A. Vishwamitra, Acta Crystallogr. B28 (1972) 1484.

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