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Non linear optical studies on semiorganic single crystal: L-arginine 4-nitrophenalate 4-nitrophenol dihydrate (LAPP)
Optics & Laser Technology 92 (2017) 168–172
Contents lists available at ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Full length article
Non linear optical studies on semiorganic single crystal: L-arginine 4nitrophenalate 4-nitrophenol dihydrate (LAPP)
MARK
⁎
M. Mahadevana, , P.K. Sankarb, G. Vinithac, M. Arivanandhand, K. Ramachandrane, P. Anandanf a
Department of Physics, Adhiparasakthi Engineering College, Melmaruvathur 603319, India Department of Physics, Karpaga Vinayaga College of Eigineering and Technology, Madurantagam 603308 India c Division of Physics, School of Advanced Science, VIT Chennai, Chennai 600127, India d Centre for Nanoscience and Technology, Anna University, Chennai 600025, India e Department of Physics, SRM University, Vadapalani Campus, Chennai 600026, India f PG & Research Department of Physics, Thiru Kolanjiappar Government Arts College, Vriddhachalam 606001, India b
A R T I C L E I N F O
A BS T RAC T
Keywords: A. Optical materials B. Crystal growth B. Radiation damage C. Refractive index C. Raman spectroscopy
L-arginine
4-nitrophenalate 4-nitrophenol dihydrate (LAPP) has been synthesized and grown by solution growth at room temperature using deionized water as a solvent. The various functional groups of the sample were identified by Fourier transform infra-red and Fourier transforms – Raman spectroscopic analyses. The Laser damage threshold of LAPP has been studied. Refractive index of LAPP single crystal was measured using Metricon prism coupler Instrument. The etching studies were carried out to study the quality of the grown crystals. The third order nonlinear optical properties of LAPP sample was analyzed by the Z-scan technique using 532 nm diode pumped CW Nd: YAG laser. The LAPP material exhibits negative optical nonlinearity. The results show that LAPP sample has potential applications in nonlinear optics and it can be exploited for optical limiting or switching.
1. Introduction Nonlinear optical (NLO) crystals are playing a dominant role in generating green laser from infra-red laser by second harmonic generation (SHG) process. Compared to inorganic NLO crystals, organic crystals are highly efficient in terms of response time, high nonlinear susceptibility, and high laser damage threshold. However, the mechanical properties of the organic materials are very weak due to Vander Waals bonding which restricts their applications. Therefore, semi-organic NLO crystals are useful for highly efficient frequency conversion applications. Since semi organic materials has physicochemical properties of both organic and inorganic crystal, many researchers focused their interest in growing semi organic single crystals [1,2]. Amino acids are the promising material for synthesis of NLO single crystals. Since it has carboxyl and amine group, it can form zwitterion when it is dissolved in a solvents and capable of forming salt with other counter ions of either organic or inorganic materials. Number of amino acid based NLO crystals has been reported and their properties were studied [3–5]. L-arginine is one of the promising amino acids which gives large numbers of derivatives with its inorganic as well as organic compounds [6–8]. After the successful investigations on the formation of NLO crystals of 4-nitrophenol ⁎
derivative with its inorganic counterpart, 4-nitrophenols derivative with amino acids were investigated and found to have great importance for SHG applications [9,10]. The design and engineering of NLO material for enhancing SHG efficiency is relatively well understood. On the other hand, the demand for efficient third order generation (THG) materials is increasing due to its importance in converting the infra-red laser radiation into intense UV radiation. Moreover, the preparation of THG material and enhancing the THG efficiency remains as a challenging task, despite of huge efforts made by the researchers. Initially, L-argininium-4-nitro phenolate monohydrate (LARP) was synthesized and the crystal structure and nonlinear optical properties were reported by Srinivasan et al. [11]. Later, Wang et al. grown Larginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) and analyzed the structural, NLO properties and compared with theoretical calculation [12]. Recently we have synthesized LAPP material and grown as a single crystal. Moreover, the structural, thermal, mechanical and optical properties of the LAPP crystals were studied and reported [13]. However, the laser damage threshold and THG properties of the LAPP crystal are not studied in details. These studies are highly essential to improve the NLO properties of the material. In the present study, single crystals have been grown from solutions prepared by
Corresponding author. E-mail address: [email protected] (M. Mahadevan).
http://dx.doi.org/10.1016/j.optlastec.2017.01.025 Received 30 June 2016; Received in revised form 23 December 2016; Accepted 24 January 2017 0030-3992/ © 2017 Elsevier Ltd. All rights reserved.
Optics & Laser Technology 92 (2017) 168–172
M. Mahadevan et al.
harvested carefully from the solution. The dimension of grown crystal has 19×12×10 mm3 as shown in Fig. 1. 3. Results and discussion 3.1. Spectral analysis FTIR spectroscopic analysis is an important technique to confirm the presence of functional groups of a material. The FTIR Spectrum of LAPP crystal is shown in Fig. 2. The functional groups of the grown LAPP crystal such as phenyl group, nitro group, carboxyl group, water molecule, etc. were properly assigned and discussed in detail. As a wide spread inter or intra molecular force, hydrogen bond has tremendous effect on the shift of FTIR spectrum. The stretching vibration of detached N–H bond generally located at 3500–3300 cm−1, but we can observe that there is a distinct absorption band at 3158 cm−1. In addition to this, the stretching vibration of C˭O band falls to 1660 cm−1. As it was proved by XRD analysis, carboxyl group acts as a proton donor in the molecule. This negative charge induces strongly hydrogen bond effect, lowering vibration frequency correspondingly. A sharp and intense peak is observed at 3629 cm−1 due to stretching vibration of OH group of LAPP material. A broad peak at 3300 cm−1 is observed due to the surface hydroxyl group of the material. Aromatic C–C stretching is observed in the range of 1500–1600 cm−1. In plane bending vibrations of benzene ring are observed in the range of 1000– 1400 cm−1. The peaks observed at less than 1000 cm−1 are due to out of plane bending of benzene ring of LAPP crystal [14]. As a consequence, the FTIR spectrum confirms the presence of various functional groups of the grown crystal. In addition to this, FT-Raman spectroscopy was used to find the molecular vibrations which are not clearly resolved in the FTIR spectrum. FT-Raman spectrum has been recorded in the range between 100 and 4000 cm−1 using BRUKER RFS 27 stand alone FT-Raman spectrometer. Due to the presence of hydrogen bonds in the molecule the vibrations are not clearly resolved in FTIR spectrum around 3000 cm−1. But it is clearly resolved in the FTRaman spectrum as shown in Fig. 3. N–H stretching of the material is observed in the Raman spectrum at 2939 cm−1. FTIR and FT-Raman modes of vibrations are compared and their assignments are given in Table 1.
Fig. 1. Photograph of as-grown LAPP Crystal.
appropriate ratio of L-arginine and 4-nitrophenol using slow evaporation solution growth method. The quality of the LAPP crystals was analyzed by etching studies. In addition, the laser damage threshold of the material has been studied and the THG of the LAPP crystal was studied by Z-scan method.
2. Material synthesis and crystal growth The purchased L-arginine (Merck Product) and 4-nitrophenol (99%) were used as source materials to synthesis the LAPP material. LAPP material was synthesized by taking the source material in appropriate ratio in excess of water. L-arginine and 4-nitrophenol were taken in equimolar ratio (1:1) and dissolved one by one in excess of water by continuous stirring. The reaction of synthesis process is illustrated in the following equation, C6H14N4O2+2C6H4NO2OH → C6H15N4O2C6H5NO3C6H4NO3 (H2O)2 After the solution became homogeneous, it was filtered and transferred to another beaker, and then the excess water was allowed to evaporate at 40 °C. Yellow color crystalline salt was obtained at the bottom of the crystallizer. The synthesized material was purified by recrystallizing for four times. It was observed that the color of the LAPP material has changed from pale yellow to dark yellow after recrystallization process. According to the solubility data, saturated solution of LAPP was prepared at constant temperature (30 °C) [12]. The solution was covered by perforated sheets and kept in a dust free place for solvent evaporation. After a period of 45 days the single crystals were
3.2. Refractive index measurement The refractive index is one of the significant properties of nonlinear
Fig. 2. FTIR spectrum recorded for LAPP crystalline powder sample.
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Fig. 3. FT-Raman spectrum recorded for LAPP crystal sample.
Table 1 Some important vibration modes of functional groups of LAPP observed in FTIR and FTRaman spectrum and their Assignments. Wave number (cm−1) FTIR
FT-Raman
3629 3438 3337 3158 – – 1909 1660 1582 1506 1457 1336 1289 1168 1108 – 518 – 705 495
– – – – 2973 2939 – – 1593 1504 1439 1325 1284 1164 1105 852 – 638 – 436
Assignments
O-H Stretching N-H asymmetric Stretching N-H Stretching N-H Symmetric Stretching CH2 asymmetric stretching NH3+ symmetric stretching C˭O Stretching N-H in plane bending Phenyl Stretching Phenyl Stretching COO- symmetric bending C-O Stretching NO2 symmetric Stretching O-H in plane bending C-C-N asymmetric Stretching C-C Stretching Phenyl C-H out plan bending O-C˭O in plane of deformation COO- in plane bending N-H rocking
Fig. 5. (a) Optical microscopic image of etched surface of LAPP crystals (etching time, t=60 s). (b) Optical microscopic image of etched surface of LAPP crystals (etching time, t=90 s).
optical materials due to its anisotropic nature which results birefringence. In order to study the refractive index, measurements were made using a fully automated computer-driven rotary table to vary the incident angle, and located the crystal propagation mode automatically [15]. To measure the refractive index of the grown crystal, a mirror polished crystal sample of size 10×10×2 mm3 was used and the sample was brought into contact with the base of a prism by means of a pneumatically operated coupling head, created a small air gap between the crystal and the prism. A laser beam was irradiated on the base of the prism and has been totally reflected at the prism base onto a photo detector. At certain incident angle (θc), called mode angle, photons could tunnel across the air gap into the crystal and entered into a
Fig. 4. Plot of intensity vs. internal angle shows the drop in intensity for refractive index measurement of LAPP.
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observed by optical microscope and the etch patterns are shown in Fig. 5a and b. As can be seen from the Fig. 5a, the etched patterns are rectangular in shape and almost the pits are aligned in same direction. The etch pattern reflects the two dimensional growth process of the crystal as the etching is the reverse process of the growth [17]. The size as well as the depth of the etch pits are drastically increases as the etching time increases (Fig. 5b). Moreover, the steps were clearly observed on the rectangular pits which confirms the layered growth process of the crystal (Fig. 5b) [17,18]. 3.4. Third order nonlinear optical property study The Z-scan technique [19] is a simple but very accurate method to determine both nonlinear index of refraction n2 and nonlinear absorption coefficient β of a material. Third-order susceptibility (Reχ(3)) is proportional to the real part of the third-order susceptibility (Reχ(3)) and Imaginary part (Imχ(3)) is proportional to the nonlinear absorption coefficient. The Z-scan experiments were performed using a 532 nm diode pumped CW Nd: YAG Laser (Coherent CompassTM215M-50), focused using a 3.5-cm focal length lens. The laser beam waist at the focus is found out to be 15.84 µm and the Rayleigh length as 1.48 mm. A 1 mm wide optical cell containing the LAPP sample in distilled water is translated across the focal region along the axial direction, i.e the direction of the laser beam propagation. The transmission of the beam through an aperture placed in the far field was measured using photo detector which was fed to the digital power meter (Field master GScoherent). For an open aperture Z-scan, a lens replaced the aperture to collect the entire laser beam transmitted through the sample. Closed aperture gives both nonlinear refraction and absorption. Open aperture gives only nonlinear absorption. Hence ratio of closed to open aperture is taken in order to get pure nonlinear refraction [20]. Fig. 6 gives a closed, open and ratio of the closed-to-open normalized Z-scan of LAPP sample in distilled water at 63% transmittance. The peak followed by a valley-normalized transmittance obtained from the closed aperture Z-scan data indicates that the sign of the refraction nonlinearity is negative, i.e., self-defocusing. The selfdefocusing effect is due to the local variation in the refractive index with the temperature. The open aperture curves show that the material exhibits saturable absorption. The peak followed by the valley in the zscan closed aperture curve exhibits the negative optical nonlinearity of the material. The third order nonlinear parameters such as nonlinear refractive index (n2=5.22×10 −8 cm2/W), nonlinear absorption coefficient β=0.49×10−4 cm/W and nonlinear susceptibility (3) (χ =1.74×10−6 esu) of the LAPP crystal were measured. The results show that the material is a potential candidate for third order nonlinear optical applications. It is worth noting that the measured value of χ(3) of LAPP crystal is larger than those of some representative third-order nonlinear optical materials such as organic polymers and organic metals [21–23].
Fig. 6. Normalized transmittance curve obtained during z-scan with closed aperture, open aperture and ratio of closed to open aperture.
guided optical propagation mode, caused a sharp drop in the intensity of light reached the detector. To a rough approximation, the angular location of the mode (dip) determines the refractive index of the crystal. The index was determined by measuring the critical angle θc for the sample-prism interface [16]. The knee observed is shown in Fig. 4 and the calculated refractive index is 1.56 and the value shows that the material is a potential candidate for nonlinear applications like optical limiting and optical switching too.
3.5. Laser damage threshold study The application of nonlinear optical crystals depends not only on the linear and nonlinear optical properties but also largely on its ability to withstand high power lasers. Laser damage threshold (LDT) is an important crystal parameter as the knowledge of which is essential for using the crystal as a nonlinear optical element in various applications involving large laser input power like frequency doubling, optical parametric processes, etc. The LDT depends on many factor like pulse duration, sample quality, focal spot geometry, experimental technique employed [24,25]. The laser damage thresholds studies were carried out for the LAPP crystals using single shot laser mode using a Qswitched Nd: YAG laser 6 ns (nanoseconds) pulse width, 10 Hz repetition rate and second harmonic wavelength of 532 nm. The calculated LDT value of LAPP is 24.3 GW/cm2 and it is relatively
3.3. Etching studies In order to find the dislocation sites and defects in the crystal, chemical etching method was used. The etching studies were carried out on the grown crystals of LAPP by using ethanol as etchant. Carl Zeiss High resolution optical microscope was used to observe the etched surfaces of the samples. The selected region of the sample was etched at different time period of 60 and 90 s. The etched patterns were 171
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[5] G. Ramesh Kumar, S. Gokul Raj, V. Mathivanan, M. Kovendhan, Raghavalu Thenneti, R. Mohan, Opt. Mater. 30 (2008) 1405–1409. [6] P. Anandan, T. Saravanan, G. Parthipan, R. Mohan Kumar, G. Bhagavannarayana, G. Ravi, R. Jayavel, Solid State Sci. 139 (2011) 915–922. [7] L. Wang, G.H. Zhang, X.T. Liu, L.N. Wang, X.Q. Wang, L.Y. Zhu, D. Xu, J. Mol. Struct. 1058 (2014) 155–162. [8] T. Baraniraj, P. Philominathan, Spectrochim. Acta A 75 (2010) 74–76. [9] M. Prakash, M. Lydia Caroline, D. Geetha, Spectrochim. Acta A 108 (2013) 32–37. [10] B. Dhanalakshmi, S. Ponnusamy, C. Muthamizhchelvan, J. Cryst. Growth 313 (2010) 30–36. [11] P. Srinivasan, Y. Vidyalakshmi, R. Gopalakrishnan, Cryst. Growth Des. 8 (2008) 2329–2334. [12] L.N. Wang, X.Q. Wang, G.H. Zhang, X.T. Liu, Z.H. Sun, G.H. Sun, L. Wang, W.T. Yu, D. Xu, Single crystal growth, crystal structure and characterization of a novel crystal: l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP), J. Cryst. Growth 327 (2011) 133–139. [13] M. Mahadevan, K. Ramachandran, P. Anandan, G. Arivanandhan, Y. Bhagavannarayana, Hayakawa, Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 133 (2014) 396–402. [14] R.J. Abraham, M. Mobli, An NMR, IR and theoretical investigation of 1H Chemical Shifts and hydrogen bonding in phenols, Mag. Reson. Chem. 45 (2007) 865–877. [15] P. Anandan, R. Jayavel, T. Saravanan, G. Parthipan, C. Vedhi, R. Mohan Kumar, Opt. Mater. 34 (2012) 1225–1230. [16] P. Anandan, G. Parthipan, T. Saravanan, R. Mohan Kumar, G. Bhagavannarayana, R. Jayavel, (15 December)Physica B: Condens. Matter 405 (24) (2010) 4951–4956. [17] A.S. Haja Hameed, P. Anandan, R. Jayavel, P. Ramasamy, G. Ravi, J. Cryst. Growth 249 (2003) 316–320. [18] M. Szurgot, Cryst. Res. Technol. 25 (1990) 71–79. [19] M. Sheik-Bahae, A.A. Said, T. Wei, D.J. Hagan, E.W. Van Stryland, Sensitive measurement of optical nonlinearities using a single beam, IEEE J. Quantum Electron. QE-26 (1990) 760–769. [20] G. Vinitha, A. Ramalingam, P.K. Palanisamy, Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 68 (2007) 1–5. [21] F. Li, Y. Song, K. Yang, S. Liu, C. Li, Appl. Phys. Lett. 71 (1997) 2073. [22] G. Ravindra Kumar, F.A. Rajgara, Appl. Phys. Lett. 67 (1995) 3871. [23] A. Clementi, N. Chiodini, A. Pleari, Appl. Phys. Lett. 84 (2004) 960. [24] S. Vanishri, J.N. Babu Reddy, H.L. Bhat, S. Ghosh, Appl. Phys. B. 88 (2007) 457–461. [25] G. Bhagavannarayana, B. Riscob, Mohd Shakir, Mat. Chem. Phys. 126 (2011) 20–23.
larger than that of KDP which is used as a reference material. Thus the LAPP crystal is a material with high LDT and it can be used for NLO device applications. 4. Conclusions Single crystals of LAPP were been grown by slow evaporation method. Various functional groups of the grown crystals were analyzed by FTIR and FT-RAMAN methods. Refractive index of LAPP single crystal was measured using Metricon prism coupler and the calculated refractive index is 1.56. The quality of the grown crystal was analyzed by etching studies. The etch pattern revealed the layered growth mechanism of the crystal. The laser damage threshold of the LAPP was determined as 24.3 GW/cm2 and the value is relatively larger than that of KDP. The THG properties of the grown crystal was analyzed and found to be a potential candidate for nonlinear optical device applications. Acknowledgements One of the Authors (M M) is grateful to Sakthi Dr. G. B. Senthil Kumar, Correspondent, Adhiparasakthi Engineering College, Melmaruvathur, India for his constant motivation and support. References [1] Z. Kotler, R. Hierle, D. Josse, J. Zyss, R. Masse, J. Opt. Soc. Am. B 9 (1992) 534–547. [2] S.R. Marder, J.W. Perry, C.P., Yakymyshyn, Chem. Mater. 6 (1994) 1137–1147. [3] A.M. Petrosyan, R.P. Sukiasyan, H.A. Karapetyan, S.S. Terzyan, R.S. Feigelson, J. Cryst. Growth 213 (2000) 103–111. [4] R.P. Sukiasyan, A.A. Karapetyan, A.M. Petrosyan, J. Mol. Struct. 888 (2008) 230–237.
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Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
Full length article
Non linear optical studies on semiorganic single crystal: L-arginine 4nitrophenalate 4-nitrophenol dihydrate (LAPP)
MARK
⁎
M. Mahadevana, , P.K. Sankarb, G. Vinithac, M. Arivanandhand, K. Ramachandrane, P. Anandanf a
Department of Physics, Adhiparasakthi Engineering College, Melmaruvathur 603319, India Department of Physics, Karpaga Vinayaga College of Eigineering and Technology, Madurantagam 603308 India c Division of Physics, School of Advanced Science, VIT Chennai, Chennai 600127, India d Centre for Nanoscience and Technology, Anna University, Chennai 600025, India e Department of Physics, SRM University, Vadapalani Campus, Chennai 600026, India f PG & Research Department of Physics, Thiru Kolanjiappar Government Arts College, Vriddhachalam 606001, India b
A R T I C L E I N F O
A BS T RAC T
Keywords: A. Optical materials B. Crystal growth B. Radiation damage C. Refractive index C. Raman spectroscopy
L-arginine
4-nitrophenalate 4-nitrophenol dihydrate (LAPP) has been synthesized and grown by solution growth at room temperature using deionized water as a solvent. The various functional groups of the sample were identified by Fourier transform infra-red and Fourier transforms – Raman spectroscopic analyses. The Laser damage threshold of LAPP has been studied. Refractive index of LAPP single crystal was measured using Metricon prism coupler Instrument. The etching studies were carried out to study the quality of the grown crystals. The third order nonlinear optical properties of LAPP sample was analyzed by the Z-scan technique using 532 nm diode pumped CW Nd: YAG laser. The LAPP material exhibits negative optical nonlinearity. The results show that LAPP sample has potential applications in nonlinear optics and it can be exploited for optical limiting or switching.
1. Introduction Nonlinear optical (NLO) crystals are playing a dominant role in generating green laser from infra-red laser by second harmonic generation (SHG) process. Compared to inorganic NLO crystals, organic crystals are highly efficient in terms of response time, high nonlinear susceptibility, and high laser damage threshold. However, the mechanical properties of the organic materials are very weak due to Vander Waals bonding which restricts their applications. Therefore, semi-organic NLO crystals are useful for highly efficient frequency conversion applications. Since semi organic materials has physicochemical properties of both organic and inorganic crystal, many researchers focused their interest in growing semi organic single crystals [1,2]. Amino acids are the promising material for synthesis of NLO single crystals. Since it has carboxyl and amine group, it can form zwitterion when it is dissolved in a solvents and capable of forming salt with other counter ions of either organic or inorganic materials. Number of amino acid based NLO crystals has been reported and their properties were studied [3–5]. L-arginine is one of the promising amino acids which gives large numbers of derivatives with its inorganic as well as organic compounds [6–8]. After the successful investigations on the formation of NLO crystals of 4-nitrophenol ⁎
derivative with its inorganic counterpart, 4-nitrophenols derivative with amino acids were investigated and found to have great importance for SHG applications [9,10]. The design and engineering of NLO material for enhancing SHG efficiency is relatively well understood. On the other hand, the demand for efficient third order generation (THG) materials is increasing due to its importance in converting the infra-red laser radiation into intense UV radiation. Moreover, the preparation of THG material and enhancing the THG efficiency remains as a challenging task, despite of huge efforts made by the researchers. Initially, L-argininium-4-nitro phenolate monohydrate (LARP) was synthesized and the crystal structure and nonlinear optical properties were reported by Srinivasan et al. [11]. Later, Wang et al. grown Larginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) and analyzed the structural, NLO properties and compared with theoretical calculation [12]. Recently we have synthesized LAPP material and grown as a single crystal. Moreover, the structural, thermal, mechanical and optical properties of the LAPP crystals were studied and reported [13]. However, the laser damage threshold and THG properties of the LAPP crystal are not studied in details. These studies are highly essential to improve the NLO properties of the material. In the present study, single crystals have been grown from solutions prepared by
Corresponding author. E-mail address: [email protected] (M. Mahadevan).
http://dx.doi.org/10.1016/j.optlastec.2017.01.025 Received 30 June 2016; Received in revised form 23 December 2016; Accepted 24 January 2017 0030-3992/ © 2017 Elsevier Ltd. All rights reserved.
Optics & Laser Technology 92 (2017) 168–172
M. Mahadevan et al.
harvested carefully from the solution. The dimension of grown crystal has 19×12×10 mm3 as shown in Fig. 1. 3. Results and discussion 3.1. Spectral analysis FTIR spectroscopic analysis is an important technique to confirm the presence of functional groups of a material. The FTIR Spectrum of LAPP crystal is shown in Fig. 2. The functional groups of the grown LAPP crystal such as phenyl group, nitro group, carboxyl group, water molecule, etc. were properly assigned and discussed in detail. As a wide spread inter or intra molecular force, hydrogen bond has tremendous effect on the shift of FTIR spectrum. The stretching vibration of detached N–H bond generally located at 3500–3300 cm−1, but we can observe that there is a distinct absorption band at 3158 cm−1. In addition to this, the stretching vibration of C˭O band falls to 1660 cm−1. As it was proved by XRD analysis, carboxyl group acts as a proton donor in the molecule. This negative charge induces strongly hydrogen bond effect, lowering vibration frequency correspondingly. A sharp and intense peak is observed at 3629 cm−1 due to stretching vibration of OH group of LAPP material. A broad peak at 3300 cm−1 is observed due to the surface hydroxyl group of the material. Aromatic C–C stretching is observed in the range of 1500–1600 cm−1. In plane bending vibrations of benzene ring are observed in the range of 1000– 1400 cm−1. The peaks observed at less than 1000 cm−1 are due to out of plane bending of benzene ring of LAPP crystal [14]. As a consequence, the FTIR spectrum confirms the presence of various functional groups of the grown crystal. In addition to this, FT-Raman spectroscopy was used to find the molecular vibrations which are not clearly resolved in the FTIR spectrum. FT-Raman spectrum has been recorded in the range between 100 and 4000 cm−1 using BRUKER RFS 27 stand alone FT-Raman spectrometer. Due to the presence of hydrogen bonds in the molecule the vibrations are not clearly resolved in FTIR spectrum around 3000 cm−1. But it is clearly resolved in the FTRaman spectrum as shown in Fig. 3. N–H stretching of the material is observed in the Raman spectrum at 2939 cm−1. FTIR and FT-Raman modes of vibrations are compared and their assignments are given in Table 1.
Fig. 1. Photograph of as-grown LAPP Crystal.
appropriate ratio of L-arginine and 4-nitrophenol using slow evaporation solution growth method. The quality of the LAPP crystals was analyzed by etching studies. In addition, the laser damage threshold of the material has been studied and the THG of the LAPP crystal was studied by Z-scan method.
2. Material synthesis and crystal growth The purchased L-arginine (Merck Product) and 4-nitrophenol (99%) were used as source materials to synthesis the LAPP material. LAPP material was synthesized by taking the source material in appropriate ratio in excess of water. L-arginine and 4-nitrophenol were taken in equimolar ratio (1:1) and dissolved one by one in excess of water by continuous stirring. The reaction of synthesis process is illustrated in the following equation, C6H14N4O2+2C6H4NO2OH → C6H15N4O2C6H5NO3C6H4NO3 (H2O)2 After the solution became homogeneous, it was filtered and transferred to another beaker, and then the excess water was allowed to evaporate at 40 °C. Yellow color crystalline salt was obtained at the bottom of the crystallizer. The synthesized material was purified by recrystallizing for four times. It was observed that the color of the LAPP material has changed from pale yellow to dark yellow after recrystallization process. According to the solubility data, saturated solution of LAPP was prepared at constant temperature (30 °C) [12]. The solution was covered by perforated sheets and kept in a dust free place for solvent evaporation. After a period of 45 days the single crystals were
3.2. Refractive index measurement The refractive index is one of the significant properties of nonlinear
Fig. 2. FTIR spectrum recorded for LAPP crystalline powder sample.
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Fig. 3. FT-Raman spectrum recorded for LAPP crystal sample.
Table 1 Some important vibration modes of functional groups of LAPP observed in FTIR and FTRaman spectrum and their Assignments. Wave number (cm−1) FTIR
FT-Raman
3629 3438 3337 3158 – – 1909 1660 1582 1506 1457 1336 1289 1168 1108 – 518 – 705 495
– – – – 2973 2939 – – 1593 1504 1439 1325 1284 1164 1105 852 – 638 – 436
Assignments
O-H Stretching N-H asymmetric Stretching N-H Stretching N-H Symmetric Stretching CH2 asymmetric stretching NH3+ symmetric stretching C˭O Stretching N-H in plane bending Phenyl Stretching Phenyl Stretching COO- symmetric bending C-O Stretching NO2 symmetric Stretching O-H in plane bending C-C-N asymmetric Stretching C-C Stretching Phenyl C-H out plan bending O-C˭O in plane of deformation COO- in plane bending N-H rocking
Fig. 5. (a) Optical microscopic image of etched surface of LAPP crystals (etching time, t=60 s). (b) Optical microscopic image of etched surface of LAPP crystals (etching time, t=90 s).
optical materials due to its anisotropic nature which results birefringence. In order to study the refractive index, measurements were made using a fully automated computer-driven rotary table to vary the incident angle, and located the crystal propagation mode automatically [15]. To measure the refractive index of the grown crystal, a mirror polished crystal sample of size 10×10×2 mm3 was used and the sample was brought into contact with the base of a prism by means of a pneumatically operated coupling head, created a small air gap between the crystal and the prism. A laser beam was irradiated on the base of the prism and has been totally reflected at the prism base onto a photo detector. At certain incident angle (θc), called mode angle, photons could tunnel across the air gap into the crystal and entered into a
Fig. 4. Plot of intensity vs. internal angle shows the drop in intensity for refractive index measurement of LAPP.
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observed by optical microscope and the etch patterns are shown in Fig. 5a and b. As can be seen from the Fig. 5a, the etched patterns are rectangular in shape and almost the pits are aligned in same direction. The etch pattern reflects the two dimensional growth process of the crystal as the etching is the reverse process of the growth [17]. The size as well as the depth of the etch pits are drastically increases as the etching time increases (Fig. 5b). Moreover, the steps were clearly observed on the rectangular pits which confirms the layered growth process of the crystal (Fig. 5b) [17,18]. 3.4. Third order nonlinear optical property study The Z-scan technique [19] is a simple but very accurate method to determine both nonlinear index of refraction n2 and nonlinear absorption coefficient β of a material. Third-order susceptibility (Reχ(3)) is proportional to the real part of the third-order susceptibility (Reχ(3)) and Imaginary part (Imχ(3)) is proportional to the nonlinear absorption coefficient. The Z-scan experiments were performed using a 532 nm diode pumped CW Nd: YAG Laser (Coherent CompassTM215M-50), focused using a 3.5-cm focal length lens. The laser beam waist at the focus is found out to be 15.84 µm and the Rayleigh length as 1.48 mm. A 1 mm wide optical cell containing the LAPP sample in distilled water is translated across the focal region along the axial direction, i.e the direction of the laser beam propagation. The transmission of the beam through an aperture placed in the far field was measured using photo detector which was fed to the digital power meter (Field master GScoherent). For an open aperture Z-scan, a lens replaced the aperture to collect the entire laser beam transmitted through the sample. Closed aperture gives both nonlinear refraction and absorption. Open aperture gives only nonlinear absorption. Hence ratio of closed to open aperture is taken in order to get pure nonlinear refraction [20]. Fig. 6 gives a closed, open and ratio of the closed-to-open normalized Z-scan of LAPP sample in distilled water at 63% transmittance. The peak followed by a valley-normalized transmittance obtained from the closed aperture Z-scan data indicates that the sign of the refraction nonlinearity is negative, i.e., self-defocusing. The selfdefocusing effect is due to the local variation in the refractive index with the temperature. The open aperture curves show that the material exhibits saturable absorption. The peak followed by the valley in the zscan closed aperture curve exhibits the negative optical nonlinearity of the material. The third order nonlinear parameters such as nonlinear refractive index (n2=5.22×10 −8 cm2/W), nonlinear absorption coefficient β=0.49×10−4 cm/W and nonlinear susceptibility (3) (χ =1.74×10−6 esu) of the LAPP crystal were measured. The results show that the material is a potential candidate for third order nonlinear optical applications. It is worth noting that the measured value of χ(3) of LAPP crystal is larger than those of some representative third-order nonlinear optical materials such as organic polymers and organic metals [21–23].
Fig. 6. Normalized transmittance curve obtained during z-scan with closed aperture, open aperture and ratio of closed to open aperture.
guided optical propagation mode, caused a sharp drop in the intensity of light reached the detector. To a rough approximation, the angular location of the mode (dip) determines the refractive index of the crystal. The index was determined by measuring the critical angle θc for the sample-prism interface [16]. The knee observed is shown in Fig. 4 and the calculated refractive index is 1.56 and the value shows that the material is a potential candidate for nonlinear applications like optical limiting and optical switching too.
3.5. Laser damage threshold study The application of nonlinear optical crystals depends not only on the linear and nonlinear optical properties but also largely on its ability to withstand high power lasers. Laser damage threshold (LDT) is an important crystal parameter as the knowledge of which is essential for using the crystal as a nonlinear optical element in various applications involving large laser input power like frequency doubling, optical parametric processes, etc. The LDT depends on many factor like pulse duration, sample quality, focal spot geometry, experimental technique employed [24,25]. The laser damage thresholds studies were carried out for the LAPP crystals using single shot laser mode using a Qswitched Nd: YAG laser 6 ns (nanoseconds) pulse width, 10 Hz repetition rate and second harmonic wavelength of 532 nm. The calculated LDT value of LAPP is 24.3 GW/cm2 and it is relatively
3.3. Etching studies In order to find the dislocation sites and defects in the crystal, chemical etching method was used. The etching studies were carried out on the grown crystals of LAPP by using ethanol as etchant. Carl Zeiss High resolution optical microscope was used to observe the etched surfaces of the samples. The selected region of the sample was etched at different time period of 60 and 90 s. The etched patterns were 171
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[5] G. Ramesh Kumar, S. Gokul Raj, V. Mathivanan, M. Kovendhan, Raghavalu Thenneti, R. Mohan, Opt. Mater. 30 (2008) 1405–1409. [6] P. Anandan, T. Saravanan, G. Parthipan, R. Mohan Kumar, G. Bhagavannarayana, G. Ravi, R. Jayavel, Solid State Sci. 139 (2011) 915–922. [7] L. Wang, G.H. Zhang, X.T. Liu, L.N. Wang, X.Q. Wang, L.Y. Zhu, D. Xu, J. Mol. Struct. 1058 (2014) 155–162. [8] T. Baraniraj, P. Philominathan, Spectrochim. Acta A 75 (2010) 74–76. [9] M. Prakash, M. Lydia Caroline, D. Geetha, Spectrochim. Acta A 108 (2013) 32–37. [10] B. Dhanalakshmi, S. Ponnusamy, C. Muthamizhchelvan, J. Cryst. Growth 313 (2010) 30–36. [11] P. Srinivasan, Y. Vidyalakshmi, R. Gopalakrishnan, Cryst. Growth Des. 8 (2008) 2329–2334. [12] L.N. Wang, X.Q. Wang, G.H. Zhang, X.T. Liu, Z.H. Sun, G.H. Sun, L. Wang, W.T. Yu, D. Xu, Single crystal growth, crystal structure and characterization of a novel crystal: l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP), J. Cryst. Growth 327 (2011) 133–139. [13] M. Mahadevan, K. Ramachandran, P. Anandan, G. Arivanandhan, Y. Bhagavannarayana, Hayakawa, Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 133 (2014) 396–402. [14] R.J. Abraham, M. Mobli, An NMR, IR and theoretical investigation of 1H Chemical Shifts and hydrogen bonding in phenols, Mag. Reson. Chem. 45 (2007) 865–877. [15] P. Anandan, R. Jayavel, T. Saravanan, G. Parthipan, C. Vedhi, R. Mohan Kumar, Opt. Mater. 34 (2012) 1225–1230. [16] P. Anandan, G. Parthipan, T. Saravanan, R. Mohan Kumar, G. Bhagavannarayana, R. Jayavel, (15 December)Physica B: Condens. Matter 405 (24) (2010) 4951–4956. [17] A.S. Haja Hameed, P. Anandan, R. Jayavel, P. Ramasamy, G. Ravi, J. Cryst. Growth 249 (2003) 316–320. [18] M. Szurgot, Cryst. Res. Technol. 25 (1990) 71–79. [19] M. Sheik-Bahae, A.A. Said, T. Wei, D.J. Hagan, E.W. Van Stryland, Sensitive measurement of optical nonlinearities using a single beam, IEEE J. Quantum Electron. QE-26 (1990) 760–769. [20] G. Vinitha, A. Ramalingam, P.K. Palanisamy, Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 68 (2007) 1–5. [21] F. Li, Y. Song, K. Yang, S. Liu, C. Li, Appl. Phys. Lett. 71 (1997) 2073. [22] G. Ravindra Kumar, F.A. Rajgara, Appl. Phys. Lett. 67 (1995) 3871. [23] A. Clementi, N. Chiodini, A. Pleari, Appl. Phys. Lett. 84 (2004) 960. [24] S. Vanishri, J.N. Babu Reddy, H.L. Bhat, S. Ghosh, Appl. Phys. B. 88 (2007) 457–461. [25] G. Bhagavannarayana, B. Riscob, Mohd Shakir, Mat. Chem. Phys. 126 (2011) 20–23.
larger than that of KDP which is used as a reference material. Thus the LAPP crystal is a material with high LDT and it can be used for NLO device applications. 4. Conclusions Single crystals of LAPP were been grown by slow evaporation method. Various functional groups of the grown crystals were analyzed by FTIR and FT-RAMAN methods. Refractive index of LAPP single crystal was measured using Metricon prism coupler and the calculated refractive index is 1.56. The quality of the grown crystal was analyzed by etching studies. The etch pattern revealed the layered growth mechanism of the crystal. The laser damage threshold of the LAPP was determined as 24.3 GW/cm2 and the value is relatively larger than that of KDP. The THG properties of the grown crystal was analyzed and found to be a potential candidate for nonlinear optical device applications. Acknowledgements One of the Authors (M M) is grateful to Sakthi Dr. G. B. Senthil Kumar, Correspondent, Adhiparasakthi Engineering College, Melmaruvathur, India for his constant motivation and support. References [1] Z. Kotler, R. Hierle, D. Josse, J. Zyss, R. Masse, J. Opt. Soc. Am. B 9 (1992) 534–547. [2] S.R. Marder, J.W. Perry, C.P., Yakymyshyn, Chem. Mater. 6 (1994) 1137–1147. [3] A.M. Petrosyan, R.P. Sukiasyan, H.A. Karapetyan, S.S. Terzyan, R.S. Feigelson, J. Cryst. Growth 213 (2000) 103–111. [4] R.P. Sukiasyan, A.A. Karapetyan, A.M. Petrosyan, J. Mol. Struct. 888 (2008) 230–237.
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