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Chemical analysis, FTIR and microhardness study to find out nonlinear optical property of l -asparagine lithium chloride: a semiorganic crystal
Microchemical Journal 110 (2013) 749–752
Contents lists available at ScienceDirect
Microchemical Journal journal homepage: www.elsevier.com/locate/microc
Chemical analysis, FTIR and microhardness study to find out nonlinear optical property of L-asparagine lithium chloride: a semiorganic crystal S. Masilamani a,⁎, A. Mohamed Musthafa b a b
Department of Physics, K. S. Rangasamy College of Technology, Tiruchengode 637 215, Tamil Nadu, India Department of Physics, Francis Xavier Engineering College, Tirunelveli 627 003, Tamil Nadu, India
a r t i c l e
i n f o
Article history: Received 18 August 2013 Received in revised form 3 September 2013 Accepted 4 September 2013 Available online 11 September 2013 Keywords: Crystal growth Semiorganic Microhardness FTIR NLO materials
a b s t r a c t In recent times semiorganic nonlinear optical material is a forefront of current research because of its importance to providing key functions of frequency conversion, light modulations and optical memory storage. Most of the organic materials have inadequate transparency, poor optical quality and low laser damage threshold. Inorganic materials have excellent mechanical and thermal properties but they possess relatively modest nonlinearity. Semiorganic materials which have combined properties of both organic and inorganic materials. In this coordination complex the organic ligand plays an important role for the nonlinear optical property. Nowadays, amino acids are more suitable organic materials for nonlinear optical applications because they contain dipolar nature − due to the presence of a protonated amino group (NH+ 3 ) and deprotonated carboxylic group (COO ). In the present study L-asparagine lithium chloride (LALC) was grown from aqueous solution by slow evaporation method. The crystalline perfection of the material was confirmed by powder X-ray diffraction. The lattice parameters were calculated by single crystal X-ray diffraction and it was found to be the LALC crystallized in orthorhombic crystal system with noncentro symmetric space group of Pna21 which is one of the essential parameters in nonlinear optical materials. The optical transparency was analyzed by UV–vis transmission spectral study and it was found to be of lower cut off wavelength of the grown crystal which is 234 nm. The presence of functional groups was identified by FTIR spectral analysis. The percentage of carbon, hydrogen and nitrogen in the crystal was calculated by chemical analysis and compared with its theoretical values. The mechanical strength was calculated by Vickers microhardness tester. The nonlinear optical efficiency of the crystal was estimated by using Kurtz Perry powder technique and it was found to be 2.08 times that of potassium dihydrogen phosphate (KDP) due to noncentro symmetric space group of good nonlinear optical material. Hence, LALC crystal is more suitable for the fabrication of optoelectronic devices. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Nonlinear optical (NLO) single crystals find a variety of applications to perform functions like electro-optic switching, optical memory storage, frequency conversion, second harmonic generation and high energy lasers for inertial confinement fusion research [1–6]. In recent years, there have been extensive researches in the investigation of nonlinear optical crystals because of their potential applications in fabrication of optoelectronic devices [7–10]. The organic crystals have large nonlinearity but they have poor mechanical and thermal stability and are susceptible for damage during processing. Moreover growth of large size single crystal is difficult to grow for fabrication of devices. Inorganic crystals have excellent mechanical and thermal properties, but possess relatively modest optical nonlinearity because of the lack of ⁎ Corresponding author at: Department of Physics, K. S. Rangasamy College of Technology, Tiruchengode, Namakkal 637215, Tamil Nadu, India. Tel.: +91 4288 274741; fax: +91 4288 274745. E-mail address: [email protected] (S. Masilamani). 0026-265X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.microc.2013.09.003
extended π-electron delocalization. Due to the above reasons, investigations have been made on semiorganic crystals which have combined properties of both organic and inorganic crystals and it is more suitable for device fabrication [11]. Amino acid crystals have subjected to extensive investigation by several researches for their excellent characteristics [12–14]. Amino acids are suitable organic materials for nonlinear optical application devices because they contain donor carboxylic (COOH) group and proton acceptor amino (NH2) group known as zwitterions which create hydrogen bonds [15]. This dipolar nature exhibits the peculiar physical and chemical properties in amino acids which makes them suitable material for the fabrication of nonlinear optical application devices. In the present work L-asparagine lithium chloride (LALC), a semi organic NLO crystal was grown from aqueous solution by slow evaporation technique. The grown crystal was subjected to various characterization techniques such as X-ray diffraction, UV–visible, Fourier transform infra red, elemental analysis, microhardness study, thermal analysis and second harmonic studies which were discussed in detail.
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2. Experimental procedure 2.1. Material synthesis and crystal growth L-asparagine
lithium chloride compound was synthesized from and lithium chloride was taken at 1:2 equimolar ratio. The required quantity of L-asparagine and lithium chloride were thoroughly dissolved by adding double distilled water according to their solubility and stirred well continuously for about three hours using magnetic stirrer with hot plate and to obtain a homogenous mixture. The solution was filtered to remove any insoluble impurities by using Whattman filter paper of pore size ten micrometer. Then, the filtered solution of LALC is transferred to borosil glass beaker and optimally closed using perforated lid in order to control the evaporation rate and kept at room temperature without disturbed position for crystallization. Finally, a well defined transparent single crystal was obtained after thirty five days due to slow evaporation. The purity of the synthesized material was further improved by successive recrystallization process. The photograph of the grown crystal of LALC is shown in Plate 1. L-asparagine
2.2. Characterization methods The powder X-ray diffraction analysis was carried out using BRUKER X-ray diffractometer with Cu Kα radiation (λ = 1.5406 Å). The single crystal XRD data of the grown crystal of LALC was obtained by using Enraf nonius (CAD4-MV3) single crystal X-ray diffratometer with MoKα radiation (λ = 0.71073 Å). The UV–visible spectrum of LALC crystal was recorded at room temperature using PerkinElmer Lambda 35 spectrometer with scan range between 190 and 1000 nm. The FTIR spectrum was recorded using Bruker Tensor 27 with ±2 resolution in the mid IR region of 400 and 4000 cm−1. The presence of carbon, hydrogen and nitrogen percentage was calculated using VARIO EL III CHNS analyzer. The microhardness study was carried out by using Shimadzu (HMV2) tester fitted with a Vickers diamond pyramidal indenter. The second harmonic generation (SHG) efficiency was also carried out using Kurtz Perry powder technique. 3. Result and discussions 3.1. X-ray diffraction analysis
3.2. UV–vis Spectral analysis The UV transmission spectrum is very important for any optical material because a nonlinear optical material is of practical use only if it has a wide transparency window [13]. This study also gives important structural information because absorption of UV and visible light involves promotion of the electrons in п and σ orbital from the ground state to higher energy states. The suitability of LALC single crystal for optical applications was known from optical transmission spectra. The recorded UV–vis transmission spectra between 190 and 1000 nm is shown in Fig. 2. The high transparency was confirmed from the recorded spectra and observed that there was no significant absorption in the range 234 to 1000 nm. This is an advantage of the use of amino acids, where the absence of strongly conjugated bonds leads to wide transparency range in the visible and UV spectral regions. The lower cut off wave length was found to be around 234 nm combined with good transparency attests to the usefulness of LALC crystal for fabrication of optoelectronic devices. 3.3. FTIR analysis The recorded Fourier transform infrared spectra of LALC crystal is shown in Fig. 3 and the tentative vibrational assignments are given in Table 1. The peak observed at 3448 cm−1 was assigned due to OH stretching vibration of COOH [16]. The absorption peak observed at 3112 cm−1 indicates asymmetric NH+ 3 stretching vibration [17]. The C\H stretching vibration was observed at 2937 cm−1 [17]. The absorption peak at 2744 and 2525 cm−1 indicates NH+ 3 symmetric stretching vibration [18]. The peak observed at 1640 cm−1 was evident that there is asymmetric NH+ 3 deformation vibration. The symmetric −1 . The presence NH+ 3 deformation vibration was observed at 1525 cm of CH deformation vibration was evident from the absorption peak at 1356 and 1305 cm−1. The peak observed at 1230 cm−1 was assigned due to C\O stretching vibration [19]. The presence of NH+ 3 rocking
Intensity (a.u)
The crystalline nature of the grown crystal was identified by taking the X-ray diffraction pattern of powder samples using X-Ray diffractometer
with Cu kα (λ = 1.5406 Å) radiation. The sample was scanned in the range of 10°–80° at the rate of 2°/min. The powder XRD pattern is shown in Fig. 1. The presence of sharp well defined Bragg's peaks confirms the good crystalline nature of the grown LALC crystal [15]. The unit cell parameters of the grown LALC crystal was obtained by using single crystal X-ray diffractometer with MoKα radiation (λ = 0.71073 Å). It was found to be LALC crystallized in orthorhombic system and space group of Pna21 with unit cell lattice parameters a = 5.46 Å; b = 7.93 Å; c = 13.29 Å; and α = β = γ = 90°, and V = 575.42 Å3 which is recognized as noncentrosymmetric, thus it satisfying one of the basic and essential requirements for second harmonic generation activity of nonlinear optical material.
2 Theta Plate 1. The photograph of LALC crystal.
Fig. 1. Powder XRD pattern of LALC crystal.
S. Masilamani, A.M. Musthafa / Microchemical Journal 110 (2013) 749–752
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Table 1 Tentative vibrational assignments of LALC crystal. Wave number (cm−1)
Tentative vibrational assignments
3448 3112 2937 2744,2525 1640 1525 1356,1305 1230 1146 562 510
OH stretching vibration of COOH [16] NH+ 3 asymmetric stretching [17] C\H stretching [17] NH+ 3 symmetric stretching [18] NH+ 3 asymmetric deformation [19] NH+ 3 symmetric deformation [19] C\H deformation [19] C\O stretching [19] NH+ 3 rocking [18] COO− symmetric stretching [16] C\C\N deformation [19]
3.5. Microhardness study
Fig. 2. UV–vis spectrum of LALC crystal.
vibration was indicated from the absorption peak at 1146 cm−1 [18]. The peak at 562 cm−1 was assigned due to COO− symmetric stretching vibration [16]. The C\C\N deformation vibration was observed at 510 cm−1 [19]. Hence, the presence of various functional groups was confirmed from the above tentative assignment. 3.4. Elemental analysis The presence of carbon, hydrogen and nitrogen percentage of LALC compound was determined by CHNS analyzer which is shown in Table 2. The observed experimental data of carbon is 20.81%; hydrogen is 4.34%; nitrogen is 11.78%. The calculated theoretical values are of carbon, 21%; hydrogen, 4.7%; and nitrogen, 12.25%. Therefore, the experimental values of CHN have a good agreement with theoretical values. Thus, the presence of expected elements in LALC crystal was confirmed.
Hardness of a material is the resistance it offers to indentation on the material. It is a measure of its resistance to local deformation [15]. It is correlated with other mechanical properties like elastic constants, yield strength, brittleness index and temperature of cracking. The microhardness have been carried out on LALC single crystals using the microhardness tester fitted with a Vickers diamond pyramid indenter for various loads ranging from 25 to 100 g for constant time indentations. The distance between any two indentations is well chosen in such a way that it is at least three times greater than the pit diagonal length in order to avoid any mutual influence of the indentations. Vickers microhardness number was calculated using the relation Hv = 1.8544P/d2 Kg/mm2, where P is the applied load in kg and d is the average diagonal length of the indentation. A graph was plotted between the hardness number (Hv) and the applied load (P) which is shown in Fig. 4. From the graph, it is observed that the hardness value increases as the load increases and attains maximum value at 100 g. At the above load of 100 g, multiple cracks were initiated on the crystal surface around the indenter. This can be explained on the basis of penetration depth of the indenter and it was due to the release of internal stress generated locally by indentation [20]. Hence, the LALC crystal was suitable material for optoelectronic device fabrication.
Fig. 3. FTIR spectrum of LALC crystal.
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Table 2 Elemental analysis of LALC crystal. Element
Theoretical (%)
Experimental (%)
C H N
21 4.70 12.25
20.81 4.47 11.78
Acknowledgments
100 95
The authors acknowledge Prof. P. K. Das, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore for extending the laser facilities for the SHG measurement. Authors also acknowledge STIC, Cochin and SAIF, IIT, Chennai for providing the analytical instrument facilities.
90
Hardness (HV)
crystal was identified by FTIR spectral analysis. The carbon, hydrogen and nitrogen percentage was found out by elemental analysis. The mechanical stability was calculated by using Vickers microhardness tester. The second harmonic generation efficiency was found to be 2.08 times higher than that of standard KDP crystal. Hence, semiorganic LALC single crystal is a more suitable material for device fabrication in optoelectronics.
85 80 75
References
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[1] Hong Luo, Jianguo Pan, Bingqian Lar, Yuebao Li, Xing Li, Lei Han, Synthesis, crystal structure and nonlinear optical property of CsV2O5, Inorg. Chem. Commun. 27 (2013) 79–81. [2] Qi Wu, Yanjun Li, Huaichuan Chen, Kui Jiang, Hua Li, Chen Zhong, Xingguo Chen, Jingui Qin, HgBrl: a promising nonlinear optical material in IR region, Inorg. Chem. Commun. 34 (2013) 1–3. [3] M. Lydia Caroline, R. Sankar, R.M. Indirani, S. Vasudevan, Growth, optical, thermal and dielectric studies of an amino acid organic nonlinear optical material: L-Alanine, Mater. Chem. Phys. 114 (2009) 490–494. [4] Min-hua Jiang, Qi Fang, Organic and semiorganic nonlinear optical materials, Adv. Mater. 11 (1999) 1147–1151. [5] Redrothu Hanumantharao, S. Kalainathan, Growth, spectroscopic, dielectric and nonlinear optical studies of semiorganic nonlinear optical crystal—L-Alanine lithium chloride, Spectrochim. Acta A 86 (2012) 80–84. [6] M.J. Roskar, P. Cunningham, M.D. Ewbank, H.O. Marcy, F.R. Vachss, L.F. Warren, R. Gappinger, R. Borwick, Salt-based approach for frequency conversion materials, Pure Appl. Opt. 5 (1996) 667–680. [7] N.J. Long, Organometallic compounds for nonlinear optics—the search of enlightenment, Angew. Chem. Int. Ed. 34 (1995) 21–38. [8] J. Zyss, Molecular nonlinear optics: materials, physics and devices, Academic Press, Boston, 1994. [9] S.R. Marder, J.E. Sohn, in: Struck (Ed.), Materials for Nonlinear Optics, Academic Press, New York, 1991. [10] In: D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules and Crystals, vol. 1 and 2, Academic Press, New York, 1987. [11] P.R. Newman, L.F. Warren, P. Cunningham, T.Y. Chang, D.E. Cooper, G.L. Burdge, et al., Semiorganics: a new class of NLO materials, Mater. Res. Soc. Proc. 173 (1990) 557–561. [12] S. Gowri, T. Umadevi, D. Sajan, C. Surendra Dlip, A. Chandramohan, N. Lawrence, Crystal growth, spectral, optical and thermal properties of semiorganic nonlinear optical material: picolinic acid and hydrochloride, Spectrochim. Acta A 110 (2013) 28–35. [13] Soma Adhikari, Tanusree Kar, Bulk single crystal growth and characterization of L-leucine—a nonlinear optical material, Mater. Chem. Phys. 133 (2012) 1055–1059. [14] K. Moovendaran, Bikshandarkoil R. Srinivasan, J. Kalyana Sundar, S.A. Martin Britto Dhas, S. Natarajan, Structural, vibrational and thermal studies of a nonlinear optical material: L-Asparagine-L-tartaric acid, Spectrochim. Acta B 92 (2012) 388–391. [15] S. Masilamani, P. Ilayabarathi, P. Maadeswaran, J. Chandrasekaran, K. Tamilarasan, Synthesis, growth and characterization of a novel semiorganic nonlinear optical single crystal, Optik 123 (2012) 1304–1306. [16] A.R. Gargaro, L.D. Barron, L. Hetch, Vibrational Raman activity of simple amino acids, J. Raman Spectrosc. 24 (1993) 91–96. [17] In: R.J.H. Clark, R.E. Hester (Eds.), Advanced in Infrared and Raman Spectroscopy, Wiley, New York, 1984. [18] R. Griffiths, J.A. de Haseth, FT-IR spectroscopy, Wiley, New York, 1986. [19] George Socrates, Infrared and Raman characteristic group frequencies, tables and charts, Third ed. John Wiley & Sons Ltd., New York, 2001. [20] B.W. Mott, Microindentation Hardness Testing, vol. 206, Butterworths, London, 1956. [21] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical material, J. Appl. Phys. 39 (1968) 3798–3813. [22] P.A. Franken, A.E. Hill, C.W. Peters, G. Weinreich, Generation of optical harmonics, Phys. Rev. Lett. 7 (1961) 118–119. [23] P. Dhanasekaran, K. Srinivasan, Studies on the growth, structural, thermal, mechanical and optical properties of the semiorganic nonlinear optical crystal L-glutamic acid hydrobromide, J. Phys. Chem. Solids 74 (2013) 934–942.
65 60 0
10
20
30
40
50
60
70
80
90
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Load (P) Fig. 4. Hardness vs. load graph of LALC crystal.
3.6. Nonlinear optical study The second harmonic generation efficiency of LALC crystal was determined from the modified version of powder technique developed by Kurtz and Perry [21]. In this technique LALC crystal was ground into a fine powder and it is filled in an air tight micro capillary tube that serves as the sample cell. A Q switched Nd:YAG laser emitting a fundamental wavelength of 1064 nm and a pulse width of 8 ns with a repetition rate of 10 Hz was used. The input laser energy incident on the sample was 1.6 mJ/pulse, an energy level optimized not to cause any chemical decomposition of the sample. The output could be seen as a bright green light (532 nm) from the sample, which confirms the frequency doubling of LALC crystal. The output light was passed through an IR filter to collect only 532 nm radiation and its energy was measured by means of a detector (photo multiplier tube) with oscilloscope assembly [22,23]. The reference material of potassium dihydrogen phosphate (KDP) of same particle size was also filled in an airtight micro capillary tube. The output beam voltage of sample material (LALC) and reference material (KDP) were found to be 16.9 mV/s and 8.1 mV/s respectively. Hence, from the above discussion the result obtained from the nonlinear optical study highlighted the SHG efficiency of the LALC crystal was 2.08 times higher than that of standard KDP crystal. 4. Conclusions The semiorganic single crystal of LALC was grown by slow evaporation solution growth method. The material crystallized in orthorhombic structure was identified by single crystal XRD analysis and good crystalline nature was confirmed by powder XRD analysis. The optical transmission study reveals that LALC crystal had good transparency in the entire visible region and there was no absorption in this range. The presence of various functional groups in the grown
Contents lists available at ScienceDirect
Microchemical Journal journal homepage: www.elsevier.com/locate/microc
Chemical analysis, FTIR and microhardness study to find out nonlinear optical property of L-asparagine lithium chloride: a semiorganic crystal S. Masilamani a,⁎, A. Mohamed Musthafa b a b
Department of Physics, K. S. Rangasamy College of Technology, Tiruchengode 637 215, Tamil Nadu, India Department of Physics, Francis Xavier Engineering College, Tirunelveli 627 003, Tamil Nadu, India
a r t i c l e
i n f o
Article history: Received 18 August 2013 Received in revised form 3 September 2013 Accepted 4 September 2013 Available online 11 September 2013 Keywords: Crystal growth Semiorganic Microhardness FTIR NLO materials
a b s t r a c t In recent times semiorganic nonlinear optical material is a forefront of current research because of its importance to providing key functions of frequency conversion, light modulations and optical memory storage. Most of the organic materials have inadequate transparency, poor optical quality and low laser damage threshold. Inorganic materials have excellent mechanical and thermal properties but they possess relatively modest nonlinearity. Semiorganic materials which have combined properties of both organic and inorganic materials. In this coordination complex the organic ligand plays an important role for the nonlinear optical property. Nowadays, amino acids are more suitable organic materials for nonlinear optical applications because they contain dipolar nature − due to the presence of a protonated amino group (NH+ 3 ) and deprotonated carboxylic group (COO ). In the present study L-asparagine lithium chloride (LALC) was grown from aqueous solution by slow evaporation method. The crystalline perfection of the material was confirmed by powder X-ray diffraction. The lattice parameters were calculated by single crystal X-ray diffraction and it was found to be the LALC crystallized in orthorhombic crystal system with noncentro symmetric space group of Pna21 which is one of the essential parameters in nonlinear optical materials. The optical transparency was analyzed by UV–vis transmission spectral study and it was found to be of lower cut off wavelength of the grown crystal which is 234 nm. The presence of functional groups was identified by FTIR spectral analysis. The percentage of carbon, hydrogen and nitrogen in the crystal was calculated by chemical analysis and compared with its theoretical values. The mechanical strength was calculated by Vickers microhardness tester. The nonlinear optical efficiency of the crystal was estimated by using Kurtz Perry powder technique and it was found to be 2.08 times that of potassium dihydrogen phosphate (KDP) due to noncentro symmetric space group of good nonlinear optical material. Hence, LALC crystal is more suitable for the fabrication of optoelectronic devices. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Nonlinear optical (NLO) single crystals find a variety of applications to perform functions like electro-optic switching, optical memory storage, frequency conversion, second harmonic generation and high energy lasers for inertial confinement fusion research [1–6]. In recent years, there have been extensive researches in the investigation of nonlinear optical crystals because of their potential applications in fabrication of optoelectronic devices [7–10]. The organic crystals have large nonlinearity but they have poor mechanical and thermal stability and are susceptible for damage during processing. Moreover growth of large size single crystal is difficult to grow for fabrication of devices. Inorganic crystals have excellent mechanical and thermal properties, but possess relatively modest optical nonlinearity because of the lack of ⁎ Corresponding author at: Department of Physics, K. S. Rangasamy College of Technology, Tiruchengode, Namakkal 637215, Tamil Nadu, India. Tel.: +91 4288 274741; fax: +91 4288 274745. E-mail address: [email protected] (S. Masilamani). 0026-265X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.microc.2013.09.003
extended π-electron delocalization. Due to the above reasons, investigations have been made on semiorganic crystals which have combined properties of both organic and inorganic crystals and it is more suitable for device fabrication [11]. Amino acid crystals have subjected to extensive investigation by several researches for their excellent characteristics [12–14]. Amino acids are suitable organic materials for nonlinear optical application devices because they contain donor carboxylic (COOH) group and proton acceptor amino (NH2) group known as zwitterions which create hydrogen bonds [15]. This dipolar nature exhibits the peculiar physical and chemical properties in amino acids which makes them suitable material for the fabrication of nonlinear optical application devices. In the present work L-asparagine lithium chloride (LALC), a semi organic NLO crystal was grown from aqueous solution by slow evaporation technique. The grown crystal was subjected to various characterization techniques such as X-ray diffraction, UV–visible, Fourier transform infra red, elemental analysis, microhardness study, thermal analysis and second harmonic studies which were discussed in detail.
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S. Masilamani, A.M. Musthafa / Microchemical Journal 110 (2013) 749–752
2. Experimental procedure 2.1. Material synthesis and crystal growth L-asparagine
lithium chloride compound was synthesized from and lithium chloride was taken at 1:2 equimolar ratio. The required quantity of L-asparagine and lithium chloride were thoroughly dissolved by adding double distilled water according to their solubility and stirred well continuously for about three hours using magnetic stirrer with hot plate and to obtain a homogenous mixture. The solution was filtered to remove any insoluble impurities by using Whattman filter paper of pore size ten micrometer. Then, the filtered solution of LALC is transferred to borosil glass beaker and optimally closed using perforated lid in order to control the evaporation rate and kept at room temperature without disturbed position for crystallization. Finally, a well defined transparent single crystal was obtained after thirty five days due to slow evaporation. The purity of the synthesized material was further improved by successive recrystallization process. The photograph of the grown crystal of LALC is shown in Plate 1. L-asparagine
2.2. Characterization methods The powder X-ray diffraction analysis was carried out using BRUKER X-ray diffractometer with Cu Kα radiation (λ = 1.5406 Å). The single crystal XRD data of the grown crystal of LALC was obtained by using Enraf nonius (CAD4-MV3) single crystal X-ray diffratometer with MoKα radiation (λ = 0.71073 Å). The UV–visible spectrum of LALC crystal was recorded at room temperature using PerkinElmer Lambda 35 spectrometer with scan range between 190 and 1000 nm. The FTIR spectrum was recorded using Bruker Tensor 27 with ±2 resolution in the mid IR region of 400 and 4000 cm−1. The presence of carbon, hydrogen and nitrogen percentage was calculated using VARIO EL III CHNS analyzer. The microhardness study was carried out by using Shimadzu (HMV2) tester fitted with a Vickers diamond pyramidal indenter. The second harmonic generation (SHG) efficiency was also carried out using Kurtz Perry powder technique. 3. Result and discussions 3.1. X-ray diffraction analysis
3.2. UV–vis Spectral analysis The UV transmission spectrum is very important for any optical material because a nonlinear optical material is of practical use only if it has a wide transparency window [13]. This study also gives important structural information because absorption of UV and visible light involves promotion of the electrons in п and σ orbital from the ground state to higher energy states. The suitability of LALC single crystal for optical applications was known from optical transmission spectra. The recorded UV–vis transmission spectra between 190 and 1000 nm is shown in Fig. 2. The high transparency was confirmed from the recorded spectra and observed that there was no significant absorption in the range 234 to 1000 nm. This is an advantage of the use of amino acids, where the absence of strongly conjugated bonds leads to wide transparency range in the visible and UV spectral regions. The lower cut off wave length was found to be around 234 nm combined with good transparency attests to the usefulness of LALC crystal for fabrication of optoelectronic devices. 3.3. FTIR analysis The recorded Fourier transform infrared spectra of LALC crystal is shown in Fig. 3 and the tentative vibrational assignments are given in Table 1. The peak observed at 3448 cm−1 was assigned due to OH stretching vibration of COOH [16]. The absorption peak observed at 3112 cm−1 indicates asymmetric NH+ 3 stretching vibration [17]. The C\H stretching vibration was observed at 2937 cm−1 [17]. The absorption peak at 2744 and 2525 cm−1 indicates NH+ 3 symmetric stretching vibration [18]. The peak observed at 1640 cm−1 was evident that there is asymmetric NH+ 3 deformation vibration. The symmetric −1 . The presence NH+ 3 deformation vibration was observed at 1525 cm of CH deformation vibration was evident from the absorption peak at 1356 and 1305 cm−1. The peak observed at 1230 cm−1 was assigned due to C\O stretching vibration [19]. The presence of NH+ 3 rocking
Intensity (a.u)
The crystalline nature of the grown crystal was identified by taking the X-ray diffraction pattern of powder samples using X-Ray diffractometer
with Cu kα (λ = 1.5406 Å) radiation. The sample was scanned in the range of 10°–80° at the rate of 2°/min. The powder XRD pattern is shown in Fig. 1. The presence of sharp well defined Bragg's peaks confirms the good crystalline nature of the grown LALC crystal [15]. The unit cell parameters of the grown LALC crystal was obtained by using single crystal X-ray diffractometer with MoKα radiation (λ = 0.71073 Å). It was found to be LALC crystallized in orthorhombic system and space group of Pna21 with unit cell lattice parameters a = 5.46 Å; b = 7.93 Å; c = 13.29 Å; and α = β = γ = 90°, and V = 575.42 Å3 which is recognized as noncentrosymmetric, thus it satisfying one of the basic and essential requirements for second harmonic generation activity of nonlinear optical material.
2 Theta Plate 1. The photograph of LALC crystal.
Fig. 1. Powder XRD pattern of LALC crystal.
S. Masilamani, A.M. Musthafa / Microchemical Journal 110 (2013) 749–752
751
Table 1 Tentative vibrational assignments of LALC crystal. Wave number (cm−1)
Tentative vibrational assignments
3448 3112 2937 2744,2525 1640 1525 1356,1305 1230 1146 562 510
OH stretching vibration of COOH [16] NH+ 3 asymmetric stretching [17] C\H stretching [17] NH+ 3 symmetric stretching [18] NH+ 3 asymmetric deformation [19] NH+ 3 symmetric deformation [19] C\H deformation [19] C\O stretching [19] NH+ 3 rocking [18] COO− symmetric stretching [16] C\C\N deformation [19]
3.5. Microhardness study
Fig. 2. UV–vis spectrum of LALC crystal.
vibration was indicated from the absorption peak at 1146 cm−1 [18]. The peak at 562 cm−1 was assigned due to COO− symmetric stretching vibration [16]. The C\C\N deformation vibration was observed at 510 cm−1 [19]. Hence, the presence of various functional groups was confirmed from the above tentative assignment. 3.4. Elemental analysis The presence of carbon, hydrogen and nitrogen percentage of LALC compound was determined by CHNS analyzer which is shown in Table 2. The observed experimental data of carbon is 20.81%; hydrogen is 4.34%; nitrogen is 11.78%. The calculated theoretical values are of carbon, 21%; hydrogen, 4.7%; and nitrogen, 12.25%. Therefore, the experimental values of CHN have a good agreement with theoretical values. Thus, the presence of expected elements in LALC crystal was confirmed.
Hardness of a material is the resistance it offers to indentation on the material. It is a measure of its resistance to local deformation [15]. It is correlated with other mechanical properties like elastic constants, yield strength, brittleness index and temperature of cracking. The microhardness have been carried out on LALC single crystals using the microhardness tester fitted with a Vickers diamond pyramid indenter for various loads ranging from 25 to 100 g for constant time indentations. The distance between any two indentations is well chosen in such a way that it is at least three times greater than the pit diagonal length in order to avoid any mutual influence of the indentations. Vickers microhardness number was calculated using the relation Hv = 1.8544P/d2 Kg/mm2, where P is the applied load in kg and d is the average diagonal length of the indentation. A graph was plotted between the hardness number (Hv) and the applied load (P) which is shown in Fig. 4. From the graph, it is observed that the hardness value increases as the load increases and attains maximum value at 100 g. At the above load of 100 g, multiple cracks were initiated on the crystal surface around the indenter. This can be explained on the basis of penetration depth of the indenter and it was due to the release of internal stress generated locally by indentation [20]. Hence, the LALC crystal was suitable material for optoelectronic device fabrication.
Fig. 3. FTIR spectrum of LALC crystal.
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Table 2 Elemental analysis of LALC crystal. Element
Theoretical (%)
Experimental (%)
C H N
21 4.70 12.25
20.81 4.47 11.78
Acknowledgments
100 95
The authors acknowledge Prof. P. K. Das, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore for extending the laser facilities for the SHG measurement. Authors also acknowledge STIC, Cochin and SAIF, IIT, Chennai for providing the analytical instrument facilities.
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Hardness (HV)
crystal was identified by FTIR spectral analysis. The carbon, hydrogen and nitrogen percentage was found out by elemental analysis. The mechanical stability was calculated by using Vickers microhardness tester. The second harmonic generation efficiency was found to be 2.08 times higher than that of standard KDP crystal. Hence, semiorganic LALC single crystal is a more suitable material for device fabrication in optoelectronics.
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References
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[1] Hong Luo, Jianguo Pan, Bingqian Lar, Yuebao Li, Xing Li, Lei Han, Synthesis, crystal structure and nonlinear optical property of CsV2O5, Inorg. Chem. Commun. 27 (2013) 79–81. [2] Qi Wu, Yanjun Li, Huaichuan Chen, Kui Jiang, Hua Li, Chen Zhong, Xingguo Chen, Jingui Qin, HgBrl: a promising nonlinear optical material in IR region, Inorg. Chem. Commun. 34 (2013) 1–3. [3] M. Lydia Caroline, R. Sankar, R.M. Indirani, S. Vasudevan, Growth, optical, thermal and dielectric studies of an amino acid organic nonlinear optical material: L-Alanine, Mater. Chem. Phys. 114 (2009) 490–494. [4] Min-hua Jiang, Qi Fang, Organic and semiorganic nonlinear optical materials, Adv. Mater. 11 (1999) 1147–1151. [5] Redrothu Hanumantharao, S. Kalainathan, Growth, spectroscopic, dielectric and nonlinear optical studies of semiorganic nonlinear optical crystal—L-Alanine lithium chloride, Spectrochim. Acta A 86 (2012) 80–84. [6] M.J. Roskar, P. Cunningham, M.D. Ewbank, H.O. Marcy, F.R. Vachss, L.F. Warren, R. Gappinger, R. Borwick, Salt-based approach for frequency conversion materials, Pure Appl. Opt. 5 (1996) 667–680. [7] N.J. Long, Organometallic compounds for nonlinear optics—the search of enlightenment, Angew. Chem. Int. Ed. 34 (1995) 21–38. [8] J. Zyss, Molecular nonlinear optics: materials, physics and devices, Academic Press, Boston, 1994. [9] S.R. Marder, J.E. Sohn, in: Struck (Ed.), Materials for Nonlinear Optics, Academic Press, New York, 1991. [10] In: D.S. Chemla, J. Zyss (Eds.), Nonlinear Optical Properties of Organic Molecules and Crystals, vol. 1 and 2, Academic Press, New York, 1987. [11] P.R. Newman, L.F. Warren, P. Cunningham, T.Y. Chang, D.E. Cooper, G.L. Burdge, et al., Semiorganics: a new class of NLO materials, Mater. Res. Soc. Proc. 173 (1990) 557–561. [12] S. Gowri, T. Umadevi, D. Sajan, C. Surendra Dlip, A. Chandramohan, N. Lawrence, Crystal growth, spectral, optical and thermal properties of semiorganic nonlinear optical material: picolinic acid and hydrochloride, Spectrochim. Acta A 110 (2013) 28–35. [13] Soma Adhikari, Tanusree Kar, Bulk single crystal growth and characterization of L-leucine—a nonlinear optical material, Mater. Chem. Phys. 133 (2012) 1055–1059. [14] K. Moovendaran, Bikshandarkoil R. Srinivasan, J. Kalyana Sundar, S.A. Martin Britto Dhas, S. Natarajan, Structural, vibrational and thermal studies of a nonlinear optical material: L-Asparagine-L-tartaric acid, Spectrochim. Acta B 92 (2012) 388–391. [15] S. Masilamani, P. Ilayabarathi, P. Maadeswaran, J. Chandrasekaran, K. Tamilarasan, Synthesis, growth and characterization of a novel semiorganic nonlinear optical single crystal, Optik 123 (2012) 1304–1306. [16] A.R. Gargaro, L.D. Barron, L. Hetch, Vibrational Raman activity of simple amino acids, J. Raman Spectrosc. 24 (1993) 91–96. [17] In: R.J.H. Clark, R.E. Hester (Eds.), Advanced in Infrared and Raman Spectroscopy, Wiley, New York, 1984. [18] R. Griffiths, J.A. de Haseth, FT-IR spectroscopy, Wiley, New York, 1986. [19] George Socrates, Infrared and Raman characteristic group frequencies, tables and charts, Third ed. John Wiley & Sons Ltd., New York, 2001. [20] B.W. Mott, Microindentation Hardness Testing, vol. 206, Butterworths, London, 1956. [21] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical material, J. Appl. Phys. 39 (1968) 3798–3813. [22] P.A. Franken, A.E. Hill, C.W. Peters, G. Weinreich, Generation of optical harmonics, Phys. Rev. Lett. 7 (1961) 118–119. [23] P. Dhanasekaran, K. Srinivasan, Studies on the growth, structural, thermal, mechanical and optical properties of the semiorganic nonlinear optical crystal L-glutamic acid hydrobromide, J. Phys. Chem. Solids 74 (2013) 934–942.
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Load (P) Fig. 4. Hardness vs. load graph of LALC crystal.
3.6. Nonlinear optical study The second harmonic generation efficiency of LALC crystal was determined from the modified version of powder technique developed by Kurtz and Perry [21]. In this technique LALC crystal was ground into a fine powder and it is filled in an air tight micro capillary tube that serves as the sample cell. A Q switched Nd:YAG laser emitting a fundamental wavelength of 1064 nm and a pulse width of 8 ns with a repetition rate of 10 Hz was used. The input laser energy incident on the sample was 1.6 mJ/pulse, an energy level optimized not to cause any chemical decomposition of the sample. The output could be seen as a bright green light (532 nm) from the sample, which confirms the frequency doubling of LALC crystal. The output light was passed through an IR filter to collect only 532 nm radiation and its energy was measured by means of a detector (photo multiplier tube) with oscilloscope assembly [22,23]. The reference material of potassium dihydrogen phosphate (KDP) of same particle size was also filled in an airtight micro capillary tube. The output beam voltage of sample material (LALC) and reference material (KDP) were found to be 16.9 mV/s and 8.1 mV/s respectively. Hence, from the above discussion the result obtained from the nonlinear optical study highlighted the SHG efficiency of the LALC crystal was 2.08 times higher than that of standard KDP crystal. 4. Conclusions The semiorganic single crystal of LALC was grown by slow evaporation solution growth method. The material crystallized in orthorhombic structure was identified by single crystal XRD analysis and good crystalline nature was confirmed by powder XRD analysis. The optical transmission study reveals that LALC crystal had good transparency in the entire visible region and there was no absorption in this range. The presence of various functional groups in the grown