- Email: [email protected]
Studies on growth, spectral and mechanical properties of new organic NLO crystal: Guanidinium 4-nitrobenzoate (GuNB)
Journal of Crystal Growth 362 (2013) 304–307
Contents lists available at SciVerse ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Studies on growth, spectral and mechanical properties of new organic NLO crystal: Guanidinium 4-nitrobenzoate (GuNB) T. Arumanayagam, P. Murugakoothan n PG and Research Department of Physics, Pachiyappa’s College, Chennai 600 030, India
a r t i c l e i n f o
a b s t r a c t
Available online 19 November 2011
A new organic nonlinear optical single crystal guanidinium 4-nitrobenzoate (GuNB) was successfully grown by solution growth using the slow evaporation technique. Solubility and metastable zone width were determined for different solvents. The structure of the grown crystal has been determined by single crystal x-ray diffraction analysis. The presence of functional groups and coordination of para nitro benzoate ions in the GuNB crystal have been identified by FTIR and FT Raman spectroscopic studies. The optical transparency range has been studied through UV–vis–NIR spectroscopy. The second harmonic generation efficiency of the grown GuNB crystal has been obtained by the Kurtz–Perry powder technique. The laser induced surface damage threshold for the grown crystal has been measured using Nd: YAG laser. The mechanical behavior has also been studied by Vicker’s microhardness test. & 2011 Elsevier B.V. All rights reserved.
Keywords: A1. Characterization A1. Recrystallization A2. Growth from solution B2. Nonlinear optic materials
1. Introduction Nonlinear optical materials find a number of applications like frequency conversion, optical switching, light modulation and optical memory storage. Recent researches reveal that the organic nonlinear optical materials are used for developing relatively lowpower laser-driven nonlinear optical system. They exhibit less optical response time but high second harmonic generation (SHG) efficiency compared to that of inorganic materials [1,2]. ‘‘In addition to this, the organic phases possess unlimited molecular engineering and also it is possible to control the absorption edges of intermolecular charge transfer compound by selecting the proper combination of donor acceptor’’. Guanidinium is a simple organic chemical compound, whose structure is related to those of amides and proteins and its specific planar configuration makes this cation as a potential H-donor in hydrogen bonds [3]. Thus researchers are very much interested in searching guanidine based organic compounds with good nonlinear properties such as guanidinium L-tartrate monohydrate, aminoguanidinium(1þ) hydrogen L-tartrate monohydrate, etc. [4–6]. ‘‘These materials exhibit good nonlinear optical response and thermal stability. In this molecular engineering series, another type of crystal structure was evident explicitly guanidinium 4-nitrobenzoate.’’ In the present work, an optically transparent pale yellow guanidinium 4-nitrobenzoate single crystal was obtained by the slow
evaporation technique and its structural, optical and mechanical properties are analyzed in detail. 2. Experimental Details 2.1. Synthesis of material The required amount of starting materials for synthesis of guanidinium 4-nitrobenzoate (GuNB) salt was calculated according to the following reaction: CðNH2 Þ3 þ þ C6 H4 NO2 COO -CðNH2 Þ3 þ C6 H4 NO2 COO High purity guanidine carbonate and 4-nitrobenzoic acid (Merck, AR grade) were mixed in the molar ratio 0.5:1.0 in aqueous solution. The pH of the working solution was measured as 7.6, adjusted the pH value of this solution to 8.3 by the addition of few drops of standard potassium hydroxide and the pH remained constant at least for 3 h, indicating the stability of the solution. ‘‘As the growth kinetics is considerably influenced by the pH of solution, it is observed that the growth rate and quality of GuNB crystals are good at the pH of 8.3.’’ The filtered solution was allowed to dry at room temperature. The purity of the synthesized salt was further improved by successive recrystallization in deionized water. 2.2. Solubility and metastable zone width measurement
n
Corresponding author. Tel.: þ91 44 26507586, Mobile: þ91 944 444 7586. E-mail address: [email protected] (P. Murugakoothan).
0022-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2011.10.063
Thermodynamically, the chemical potential of the pure solid is equal to the chemical potential of the same solute in the saturated
T. Arumanayagam, P. Murugakoothan / Journal of Crystal Growth 362 (2013) 304–307
Concentration (g/100 mL)
14 12 10
Concentration (g/100 mL)
solution. Also the growth rate of the crystal depends on its solubility and temperature. Hence solubility is one of the most important factors for bulk crystal growth. The synthesized salt of GuNB was further purified by repeated recrystallization process. ‘‘The rate of diffusion of growth units are mainly depends on the solute–solvent interactions, which can be effectively tuned by means of providing mixed solvents instead of single solvent.’’ The solubility of GuNB for different solvents such as water and water– ethanol (1:1) in the temperature range 30–50 1C is determined. Solubility study has been carried out using a constant temperature bath attached with a temperature indicator and a programmer. Initially, the temperature has been maintained at 30 1C and the synthesized salt is added step by step to 100 mL of de-ionized water in an air-tight container kept on the magnetic stirrer in the temperature bath. The addition of the salt and the stirring is continued till supersaturation is achieved. Then 10 mL of the solution was pipetted out and taken in a beaker and it is warmed up till the solvent has completely evaporated. By measuring the amount of salt present in the beaker, the solubility at a particular temperature in de-ionized water is determined. In the same manner, the amount of salt dissolved in 100 mL at 35, 40, 45 and 50 1C has been determined. The solubility curve of GuNB for different solvents is presented in Fig. 1(a). The solubility of GuNB is found to be higher in water–ethanol mixed solvent and it has a positive slope, indicating the possibility of growth of GuNB by both slow cooling and slow evaporation methods. Metastable zone width is an essential parameter for the growth of large size single crystal from solution, since it is the direct measure of the stability of the solution in the supersaturated region. Metastable zone width is determined by dissolving the recrystallized salt of GuNB in water–ethanol mixed solvent. The solution was stirred for about 6 h continuously for stabilization and then the temperature of the bath was reduced at a rate of 5 1C/hour. The temperature at which the first speck of a particle appeared is noted as nucleation temperature. The difference in temperature between the saturated temperature and the nucleation temperature is regarded to be the metastable zone width of the sample. The metastable zone width of GuNB in water–ethanol solvent is given in Fig. 1(b). From the graph it is clear that the metastable zone width decrease with increase of saturation temperature. The larger width shows that the growth of GuNB is suitable for slow evaporation and slow cooling technique.
8
solubility curve nucleation curve
10
2.3. Crystal growth The saturated solution of GuNB at 40 1C was prepared using recrystallized GuNB crystalline material in accordance with the solubility data. Small crystals free of macro defects, obtained by the spontaneous nucleation from the water–ethanol solution of GuNB were selected as seed crystals. For getting the optimum super saturation at this temperature, the solution was tested by checking the dissolution of a seed crystal over a period of two days. Then the solution was allowed to cool at the rate of 0.03 1C/ day till the room temperature was reached. Optically transparent pale yellow color single crystal GuNB of molecular formula C8H10N4O4 with dimension 25 7 2 mm3 is harvested after a period of 23 days. Fig. 2 shows the photograph of as grown GuNB single crystal.
2.4. Characterization The single crystal X-ray diffraction data of the grown GuNB single crystal was obtained using ENRAF NONIUS (AD4-MV3) single crystal X-ray diffractometer. FTIR and FT Raman spectra were recorded to understand the chemical bonding and molecular structure of GuNB. The FTIR spectrum was recorded in the range 400–4000 cm 1 by PERKIN-ELMER spectrometer using the KBr pellet technique. FT Raman spectrum was recorded using FTRAMAN spectrometer (Perkin-Elmer GX 2000) in the range 4000 400 cm 1. Kurtz and Perry powder method was employed to measure the second harmonic generation (SHG) efficiency of the grown GuNB crystal. Vicker’s microhardness number of the material was measured using the REICHERT MD 4000E ultra microhardness tester fitted with a diamond pyramidal indenter. The surface laser damage threshold of GuNB crystal was determined using a Q-switched Nd: YAG laser with 10 Hz pulse repetition rate operating in TEM00 mode.
3. Result and discussion 3.1. X-ray diffraction study The XRD data revealed that the grown crystal belongs to the monoclinic crystallographic system with non-centrosymmetric space group P21. The unit cell parameters obtained are a¼11.13 ˚ b ¼6.64 (2) A, ˚ c¼6.94 (2) A, ˚ b ¼107.971 and v ¼512.9 (3) A˚ 3. (2) A, The obtained lattice parameter values are in good agreement with the reported literature values [7].
8
6
4 10
20 30 40 Temperature (°C)
50
6 4
water water-ethanol
2 20
25
30
35 40 Temperature (°C)
45
50
Fig. 1. (a) Variation of solubility with temperature for GuNB. 1(b) Metastable zone width of GuNB.
305
Fig. 2. Photograph of grown GuNB single crystal.
306
T. Arumanayagam, P. Murugakoothan / Journal of Crystal Growth 362 (2013) 304–307
3.2. Spectroscopic studies
3.4. Laser damage threshold (LDT) and microhardness studies
The compound GuNB can be easily identified using spectroscopic studies such as FT-IR and FT-Raman spectroscopy. The FT-IR and FTRaman spectra for GuNB are presented in Fig. 3. On examining the FT-IR spectra for GuNB, the high-frequency absorption peaks observed at 3485 cm 1and 3382 cm 1 are assigned to NH2 asymmetric and symmetric stretching mode [8], in which symmetric stretching is active but asymmetric stretching is relatively weak as obtained from Raman spectrum. The broad absorption band at 3105 cm 1 in the IR and Raman shift at 3098 cm 1 are assigned to aromatic C–OH symmetric stretching vibration. The strong characteristic peak in IR spectrum found at 1663 cm 1 the respective Raman shift line that occur at 1602 cm 1 probably corresponds to stretching vibration of C¼O bond in COOH group [9]. The nitro group NO2 had characteristic bands caused by asymmetric and symmetric stretching vibrations. Symmetric stretching vibration gives intense bands in both IR and Raman spectra, while asymmetric stretching is intensive in the IR and relatively weak in the Raman spectrum [10].
One of the device criteria for a NLO crystal to perform as a device is its resistance to laser damage, since high optical intensities are involved in nonlinear process. Laser damage threshold in materials is often very complex involving the various processes like electron avalanche, multiple photon absorption and photo-ionization by thermal absorption. In addition to the thermal effect, a function of pulse duration, maximum pulse power, pulse wavelength and focal point radius are also involved. In the case of multiple shot experiments LDT depends on repetition rate [12]. In the present study, an actively Q-switched Nd: YAG laser for 20 ns pulse width was used. Output intensity of the laser was controlled with a variable attenuator and delivered to the test sample located at the near focusing of the converging lens. The energy density of the input laser beam for which the crystal gets damage was recorded using power meter during the
100
80
The optical transmittance of grown GuNB crystal ‘‘of thickness 2 mm’’ has been carried out between the wavelength range 200 nm and 2000 nm and the spectrum is presented in Fig. 4. From the spectrum it is clear that the grown crystal exhibit high transparency in the entire visible region with the lower cut off wavelength of 380 nm. The second harmonic generation efficiency of GuNB has been measured by the Kurtz and Perry powder technique [11]. The SHG behavior was confirmed from the output of the laser beam, which had bright green emission (l ¼532 nm) from the powder sample. The second harmonic signal of 35 mV was obtained for an input energy of 31 mJ/pulse, while the standard KDP crystal gives a SHG signal of 11 mV for the same input energy. It shows that the SHG efficiency of GuNB is 3.3 times that of standard NLO material, KDP.
Transmittance (%)
3.3. Linear and nonlinear optical studies
60
40
20
0 400
800 1200 Wavelength (nm)
Fig. 4. UV–vis–NIR transmittance spectra of GuNB crystal.
100
511
670 551 727 538
3098
1501
0.010
633
1009
0.015
865
1104
1602
0.020
3379
Raman intensity
0.025
0.005
803
1663 1556 1512 1378 1368 1339 1343
3105
40
0 0.030
885
1008 1102
60
3485 3382
%T
80
20
0.000 4000
3500
3000
2500
1600
2000
1500
Wavenumber (cm-1) Fig. 3. FTIR and FT Raman spectra of GuNB.
1000
500
2000
T. Arumanayagam, P. Murugakoothan / Journal of Crystal Growth 362 (2013) 304–307
Table 1 LDT value of the GuNB crystal along with other important NLO crystals. Compound
Laser damage threshold (GW/cm2)
Potassium dihydrogen phosphate Urea Methyl p-hydroxybenzoate Benzimidazole Guanidinium 4-nitrobenzoate
0.20a 1.50a 2.77a 2.90a 2.55b
a b
Ref. [14]. Present work.
35 (001) (101)
30
HV (kg/mm2)
25
307
shows that the hardness increases gradually with the increase of load. The hardness number for the (001) and (010) planes are different for the same applied load. The maximum Hv for (001) plane is calculated as 32.5 kg/mm2 for the load of 100 g and almost constant up to 115 g but for (010) plane, the value of Hv is 23.5 kg/mm2 for the load of 80 g and thereafter, it suddenly decreases. This result reveals that the hardness of the plane (001) is higher than that of (010) plane. This confirms that the crystal exhibit microhardness anisotropy. The anisotropy coefficient was calculated from the relation, A¼ DHV/HV, where DHV is the difference in microhardness of the two planes and HV is the maximum value of hardness of the crystal [15]. The anisotropy coefficient of GuNB crystal is calculated to be 27.7%. The work hardening coefficient ‘n’ was calculated from Meyer’s law, P¼ kdn connecting load P and average diagonal length d of the indentation, where k be the material constant. The work hardening coefficient of grown crystal for the (001) plane is found to be 2.23 by taking a slope in the straight line of the graph drawn between log d and log P. According to Hanneeman [16], n should be between 1 and 1.6 for hard materials and above 1.6 for soft one. Thus the grown GuNB crystal belongs to soft material category.
4. Conclusion
20
15
10
5 20
40
60
80
100
120
Load P (x10-3 kg) Fig. 5. Variation of Vicker’s hardness number with applied load of GuNB.
laser radiation. The surface damage threshold of the crystal was calculated using the formula, viz., Power density, P(d) ¼E/tA, where E is the energy (mJ), t is the pulse width (ns) and A is the area of the circular spot size (cm2). Multiple shot LDT measurements were made on the well polished (001) plane of the grown crystal. The beam spot size on the sample was 1 mm and the energy was measured as 40 mJ. The LDT value for the grown GuNB crystal is calculated to be 2.55 GW/cm2. In general the multiple shot LDT value is 1/3 times of single shot value [13]. Recent investigations of LDT in various optical materials by ns pulse have shown that the temperature at the damage site reaches very high, in the order of 1000 K. The comparisons of LDT value of the present sample with some other NLO crystals are given in Table 1. As seen from the table, the laser damage threshold of GuNB is higher than KDP and urea crystals [14]. In order to study the mechanical properties, microhardness measurements have carried out on GuNB single crystals. Smooth surfaces of the grown crystal were subjected to the Vicker’s microhardness test at room temperature using a Leitz Wetzler hardness tester with diamond pyramidal indenter. The load of different magnitudes was applied for a fixed interval time of 5 s. The microhardness number Hv of the crystal was calculated using the standard formula Hv ¼1.8544 P/d2 in kg/mm2, where P is the applied load and d is the average diagonal length of the indentation, which is measured by a calibrated microscope. A graph plotted between hardness number (Hv) and applied load P is depicted in Fig. 5. The graph
A potential new organic nonlinear optical GuNB single crystal was successfully grown by the slow evaporation technique. Single crystal XRD confirmed that the grown crystal belongs to the monoclinic system with the non-centrosymmetric space group P21. The spectroscopic analyses reveal the functional groups and mode of vibrations of the grown GuNB crystal. The grown crystal has a wide transparency window from 380 to 1800 nm thus confirming the suitability of this material for optical applications. The powder second harmonic generation efficiency of GuNB is about 3.3 times that of KDP. The crystal exhibits high laser damage threshold, which is a favorable property for nonlinear optical applications. The Vicker’s microhardness values measured on the different planes of GuNB crystal indicate high mechanical strength and microhardness anisotropy. References [1] M. Kitazawa, R. Higuchi, M. Takahashi, Applied Physics Letters 64 (1994) 2477. [2] W.S. Wang, M.D. Aggarwal, J. Choi, T. Gebre, A.D. Shields, B.G. Penn, D.O. Frazier, Journal of Crystal Growth 198 (1999) 578. [3] J.P. Jasinski, R.J. Butcher, M.T. Swamy, H.S. Yathirajan, A.R. Ramesha, Acta Crystallographica E 65 (2009) o2788. ¨ ¨ [4] W. Krumbe, S. Haussuhl, R. Frohlich, Zeitschrift fur Kristallographie 187 (1989) 309. [5] Zorka Machova, Ivan Nemec, Karel Teubner, Petr Nemec, Premysl Vanek, Zdenk Micka, Journal of Molecular Structure 832 (2007) 101. [6] V. Siva shanker, R. Siddeswaran, T. Bharthasarathi, P. Murugakoothan, Journal of Crystal Growth 311 (2009) 2709. [7] J.M. Adams, R.G. Pritchard, Journal of Applied Crystallography 8 (1975) 392. [8] M. Drozd, Spectrachimica Acta Part A 65 (2006) 1069. [9] X.M. Yang, D.A. Tryk, K. Hashimoto, A. Fujishima, Journal of Physical Chemistry B 102 (1998) 4933. [10] H.A. Petrosyan, H.A. Apetyan, A.M. Petrosyan, Journal of Molecular Structure 794 (2006) 160. [11] S.K. Kurtz, T.T. Perry, Journal of Applied Physics 39 (1968) 3798. [12] S. Vanishri, J.N. Babu Reddy, H.I. Bhat, S. GhoSh, Applied Physics B 88 (2007) 457. [13] S. Boomadevi, H.P. Mittal, R. Dhanasekaran, Journal of Crystal Growth 261 (2004) 55. [14] N. Vijayan, G. Bhagavannarayana, K.R. Ramesh, R. Gopalakrisnan, K.K. Maurya, P. Ramasamy, Crystal Growth and Design 6 (2006) 1542. [15] A. Bhaskaran, C.M. Ragavan, R. Sankar, R. Mohankumar, R. Jayavel, Crystal Research and Technology 42 (2007) 477. [16] M. Hanneeman, Metallurgia Manchu 23 (1941) 135.
Contents lists available at SciVerse ScienceDirect
Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro
Studies on growth, spectral and mechanical properties of new organic NLO crystal: Guanidinium 4-nitrobenzoate (GuNB) T. Arumanayagam, P. Murugakoothan n PG and Research Department of Physics, Pachiyappa’s College, Chennai 600 030, India
a r t i c l e i n f o
a b s t r a c t
Available online 19 November 2011
A new organic nonlinear optical single crystal guanidinium 4-nitrobenzoate (GuNB) was successfully grown by solution growth using the slow evaporation technique. Solubility and metastable zone width were determined for different solvents. The structure of the grown crystal has been determined by single crystal x-ray diffraction analysis. The presence of functional groups and coordination of para nitro benzoate ions in the GuNB crystal have been identified by FTIR and FT Raman spectroscopic studies. The optical transparency range has been studied through UV–vis–NIR spectroscopy. The second harmonic generation efficiency of the grown GuNB crystal has been obtained by the Kurtz–Perry powder technique. The laser induced surface damage threshold for the grown crystal has been measured using Nd: YAG laser. The mechanical behavior has also been studied by Vicker’s microhardness test. & 2011 Elsevier B.V. All rights reserved.
Keywords: A1. Characterization A1. Recrystallization A2. Growth from solution B2. Nonlinear optic materials
1. Introduction Nonlinear optical materials find a number of applications like frequency conversion, optical switching, light modulation and optical memory storage. Recent researches reveal that the organic nonlinear optical materials are used for developing relatively lowpower laser-driven nonlinear optical system. They exhibit less optical response time but high second harmonic generation (SHG) efficiency compared to that of inorganic materials [1,2]. ‘‘In addition to this, the organic phases possess unlimited molecular engineering and also it is possible to control the absorption edges of intermolecular charge transfer compound by selecting the proper combination of donor acceptor’’. Guanidinium is a simple organic chemical compound, whose structure is related to those of amides and proteins and its specific planar configuration makes this cation as a potential H-donor in hydrogen bonds [3]. Thus researchers are very much interested in searching guanidine based organic compounds with good nonlinear properties such as guanidinium L-tartrate monohydrate, aminoguanidinium(1þ) hydrogen L-tartrate monohydrate, etc. [4–6]. ‘‘These materials exhibit good nonlinear optical response and thermal stability. In this molecular engineering series, another type of crystal structure was evident explicitly guanidinium 4-nitrobenzoate.’’ In the present work, an optically transparent pale yellow guanidinium 4-nitrobenzoate single crystal was obtained by the slow
evaporation technique and its structural, optical and mechanical properties are analyzed in detail. 2. Experimental Details 2.1. Synthesis of material The required amount of starting materials for synthesis of guanidinium 4-nitrobenzoate (GuNB) salt was calculated according to the following reaction: CðNH2 Þ3 þ þ C6 H4 NO2 COO -CðNH2 Þ3 þ C6 H4 NO2 COO High purity guanidine carbonate and 4-nitrobenzoic acid (Merck, AR grade) were mixed in the molar ratio 0.5:1.0 in aqueous solution. The pH of the working solution was measured as 7.6, adjusted the pH value of this solution to 8.3 by the addition of few drops of standard potassium hydroxide and the pH remained constant at least for 3 h, indicating the stability of the solution. ‘‘As the growth kinetics is considerably influenced by the pH of solution, it is observed that the growth rate and quality of GuNB crystals are good at the pH of 8.3.’’ The filtered solution was allowed to dry at room temperature. The purity of the synthesized salt was further improved by successive recrystallization in deionized water. 2.2. Solubility and metastable zone width measurement
n
Corresponding author. Tel.: þ91 44 26507586, Mobile: þ91 944 444 7586. E-mail address: [email protected] (P. Murugakoothan).
0022-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2011.10.063
Thermodynamically, the chemical potential of the pure solid is equal to the chemical potential of the same solute in the saturated
T. Arumanayagam, P. Murugakoothan / Journal of Crystal Growth 362 (2013) 304–307
Concentration (g/100 mL)
14 12 10
Concentration (g/100 mL)
solution. Also the growth rate of the crystal depends on its solubility and temperature. Hence solubility is one of the most important factors for bulk crystal growth. The synthesized salt of GuNB was further purified by repeated recrystallization process. ‘‘The rate of diffusion of growth units are mainly depends on the solute–solvent interactions, which can be effectively tuned by means of providing mixed solvents instead of single solvent.’’ The solubility of GuNB for different solvents such as water and water– ethanol (1:1) in the temperature range 30–50 1C is determined. Solubility study has been carried out using a constant temperature bath attached with a temperature indicator and a programmer. Initially, the temperature has been maintained at 30 1C and the synthesized salt is added step by step to 100 mL of de-ionized water in an air-tight container kept on the magnetic stirrer in the temperature bath. The addition of the salt and the stirring is continued till supersaturation is achieved. Then 10 mL of the solution was pipetted out and taken in a beaker and it is warmed up till the solvent has completely evaporated. By measuring the amount of salt present in the beaker, the solubility at a particular temperature in de-ionized water is determined. In the same manner, the amount of salt dissolved in 100 mL at 35, 40, 45 and 50 1C has been determined. The solubility curve of GuNB for different solvents is presented in Fig. 1(a). The solubility of GuNB is found to be higher in water–ethanol mixed solvent and it has a positive slope, indicating the possibility of growth of GuNB by both slow cooling and slow evaporation methods. Metastable zone width is an essential parameter for the growth of large size single crystal from solution, since it is the direct measure of the stability of the solution in the supersaturated region. Metastable zone width is determined by dissolving the recrystallized salt of GuNB in water–ethanol mixed solvent. The solution was stirred for about 6 h continuously for stabilization and then the temperature of the bath was reduced at a rate of 5 1C/hour. The temperature at which the first speck of a particle appeared is noted as nucleation temperature. The difference in temperature between the saturated temperature and the nucleation temperature is regarded to be the metastable zone width of the sample. The metastable zone width of GuNB in water–ethanol solvent is given in Fig. 1(b). From the graph it is clear that the metastable zone width decrease with increase of saturation temperature. The larger width shows that the growth of GuNB is suitable for slow evaporation and slow cooling technique.
8
solubility curve nucleation curve
10
2.3. Crystal growth The saturated solution of GuNB at 40 1C was prepared using recrystallized GuNB crystalline material in accordance with the solubility data. Small crystals free of macro defects, obtained by the spontaneous nucleation from the water–ethanol solution of GuNB were selected as seed crystals. For getting the optimum super saturation at this temperature, the solution was tested by checking the dissolution of a seed crystal over a period of two days. Then the solution was allowed to cool at the rate of 0.03 1C/ day till the room temperature was reached. Optically transparent pale yellow color single crystal GuNB of molecular formula C8H10N4O4 with dimension 25 7 2 mm3 is harvested after a period of 23 days. Fig. 2 shows the photograph of as grown GuNB single crystal.
2.4. Characterization The single crystal X-ray diffraction data of the grown GuNB single crystal was obtained using ENRAF NONIUS (AD4-MV3) single crystal X-ray diffractometer. FTIR and FT Raman spectra were recorded to understand the chemical bonding and molecular structure of GuNB. The FTIR spectrum was recorded in the range 400–4000 cm 1 by PERKIN-ELMER spectrometer using the KBr pellet technique. FT Raman spectrum was recorded using FTRAMAN spectrometer (Perkin-Elmer GX 2000) in the range 4000 400 cm 1. Kurtz and Perry powder method was employed to measure the second harmonic generation (SHG) efficiency of the grown GuNB crystal. Vicker’s microhardness number of the material was measured using the REICHERT MD 4000E ultra microhardness tester fitted with a diamond pyramidal indenter. The surface laser damage threshold of GuNB crystal was determined using a Q-switched Nd: YAG laser with 10 Hz pulse repetition rate operating in TEM00 mode.
3. Result and discussion 3.1. X-ray diffraction study The XRD data revealed that the grown crystal belongs to the monoclinic crystallographic system with non-centrosymmetric space group P21. The unit cell parameters obtained are a¼11.13 ˚ b ¼6.64 (2) A, ˚ c¼6.94 (2) A, ˚ b ¼107.971 and v ¼512.9 (3) A˚ 3. (2) A, The obtained lattice parameter values are in good agreement with the reported literature values [7].
8
6
4 10
20 30 40 Temperature (°C)
50
6 4
water water-ethanol
2 20
25
30
35 40 Temperature (°C)
45
50
Fig. 1. (a) Variation of solubility with temperature for GuNB. 1(b) Metastable zone width of GuNB.
305
Fig. 2. Photograph of grown GuNB single crystal.
306
T. Arumanayagam, P. Murugakoothan / Journal of Crystal Growth 362 (2013) 304–307
3.2. Spectroscopic studies
3.4. Laser damage threshold (LDT) and microhardness studies
The compound GuNB can be easily identified using spectroscopic studies such as FT-IR and FT-Raman spectroscopy. The FT-IR and FTRaman spectra for GuNB are presented in Fig. 3. On examining the FT-IR spectra for GuNB, the high-frequency absorption peaks observed at 3485 cm 1and 3382 cm 1 are assigned to NH2 asymmetric and symmetric stretching mode [8], in which symmetric stretching is active but asymmetric stretching is relatively weak as obtained from Raman spectrum. The broad absorption band at 3105 cm 1 in the IR and Raman shift at 3098 cm 1 are assigned to aromatic C–OH symmetric stretching vibration. The strong characteristic peak in IR spectrum found at 1663 cm 1 the respective Raman shift line that occur at 1602 cm 1 probably corresponds to stretching vibration of C¼O bond in COOH group [9]. The nitro group NO2 had characteristic bands caused by asymmetric and symmetric stretching vibrations. Symmetric stretching vibration gives intense bands in both IR and Raman spectra, while asymmetric stretching is intensive in the IR and relatively weak in the Raman spectrum [10].
One of the device criteria for a NLO crystal to perform as a device is its resistance to laser damage, since high optical intensities are involved in nonlinear process. Laser damage threshold in materials is often very complex involving the various processes like electron avalanche, multiple photon absorption and photo-ionization by thermal absorption. In addition to the thermal effect, a function of pulse duration, maximum pulse power, pulse wavelength and focal point radius are also involved. In the case of multiple shot experiments LDT depends on repetition rate [12]. In the present study, an actively Q-switched Nd: YAG laser for 20 ns pulse width was used. Output intensity of the laser was controlled with a variable attenuator and delivered to the test sample located at the near focusing of the converging lens. The energy density of the input laser beam for which the crystal gets damage was recorded using power meter during the
100
80
The optical transmittance of grown GuNB crystal ‘‘of thickness 2 mm’’ has been carried out between the wavelength range 200 nm and 2000 nm and the spectrum is presented in Fig. 4. From the spectrum it is clear that the grown crystal exhibit high transparency in the entire visible region with the lower cut off wavelength of 380 nm. The second harmonic generation efficiency of GuNB has been measured by the Kurtz and Perry powder technique [11]. The SHG behavior was confirmed from the output of the laser beam, which had bright green emission (l ¼532 nm) from the powder sample. The second harmonic signal of 35 mV was obtained for an input energy of 31 mJ/pulse, while the standard KDP crystal gives a SHG signal of 11 mV for the same input energy. It shows that the SHG efficiency of GuNB is 3.3 times that of standard NLO material, KDP.
Transmittance (%)
3.3. Linear and nonlinear optical studies
60
40
20
0 400
800 1200 Wavelength (nm)
Fig. 4. UV–vis–NIR transmittance spectra of GuNB crystal.
100
511
670 551 727 538
3098
1501
0.010
633
1009
0.015
865
1104
1602
0.020
3379
Raman intensity
0.025
0.005
803
1663 1556 1512 1378 1368 1339 1343
3105
40
0 0.030
885
1008 1102
60
3485 3382
%T
80
20
0.000 4000
3500
3000
2500
1600
2000
1500
Wavenumber (cm-1) Fig. 3. FTIR and FT Raman spectra of GuNB.
1000
500
2000
T. Arumanayagam, P. Murugakoothan / Journal of Crystal Growth 362 (2013) 304–307
Table 1 LDT value of the GuNB crystal along with other important NLO crystals. Compound
Laser damage threshold (GW/cm2)
Potassium dihydrogen phosphate Urea Methyl p-hydroxybenzoate Benzimidazole Guanidinium 4-nitrobenzoate
0.20a 1.50a 2.77a 2.90a 2.55b
a b
Ref. [14]. Present work.
35 (001) (101)
30
HV (kg/mm2)
25
307
shows that the hardness increases gradually with the increase of load. The hardness number for the (001) and (010) planes are different for the same applied load. The maximum Hv for (001) plane is calculated as 32.5 kg/mm2 for the load of 100 g and almost constant up to 115 g but for (010) plane, the value of Hv is 23.5 kg/mm2 for the load of 80 g and thereafter, it suddenly decreases. This result reveals that the hardness of the plane (001) is higher than that of (010) plane. This confirms that the crystal exhibit microhardness anisotropy. The anisotropy coefficient was calculated from the relation, A¼ DHV/HV, where DHV is the difference in microhardness of the two planes and HV is the maximum value of hardness of the crystal [15]. The anisotropy coefficient of GuNB crystal is calculated to be 27.7%. The work hardening coefficient ‘n’ was calculated from Meyer’s law, P¼ kdn connecting load P and average diagonal length d of the indentation, where k be the material constant. The work hardening coefficient of grown crystal for the (001) plane is found to be 2.23 by taking a slope in the straight line of the graph drawn between log d and log P. According to Hanneeman [16], n should be between 1 and 1.6 for hard materials and above 1.6 for soft one. Thus the grown GuNB crystal belongs to soft material category.
4. Conclusion
20
15
10
5 20
40
60
80
100
120
Load P (x10-3 kg) Fig. 5. Variation of Vicker’s hardness number with applied load of GuNB.
laser radiation. The surface damage threshold of the crystal was calculated using the formula, viz., Power density, P(d) ¼E/tA, where E is the energy (mJ), t is the pulse width (ns) and A is the area of the circular spot size (cm2). Multiple shot LDT measurements were made on the well polished (001) plane of the grown crystal. The beam spot size on the sample was 1 mm and the energy was measured as 40 mJ. The LDT value for the grown GuNB crystal is calculated to be 2.55 GW/cm2. In general the multiple shot LDT value is 1/3 times of single shot value [13]. Recent investigations of LDT in various optical materials by ns pulse have shown that the temperature at the damage site reaches very high, in the order of 1000 K. The comparisons of LDT value of the present sample with some other NLO crystals are given in Table 1. As seen from the table, the laser damage threshold of GuNB is higher than KDP and urea crystals [14]. In order to study the mechanical properties, microhardness measurements have carried out on GuNB single crystals. Smooth surfaces of the grown crystal were subjected to the Vicker’s microhardness test at room temperature using a Leitz Wetzler hardness tester with diamond pyramidal indenter. The load of different magnitudes was applied for a fixed interval time of 5 s. The microhardness number Hv of the crystal was calculated using the standard formula Hv ¼1.8544 P/d2 in kg/mm2, where P is the applied load and d is the average diagonal length of the indentation, which is measured by a calibrated microscope. A graph plotted between hardness number (Hv) and applied load P is depicted in Fig. 5. The graph
A potential new organic nonlinear optical GuNB single crystal was successfully grown by the slow evaporation technique. Single crystal XRD confirmed that the grown crystal belongs to the monoclinic system with the non-centrosymmetric space group P21. The spectroscopic analyses reveal the functional groups and mode of vibrations of the grown GuNB crystal. The grown crystal has a wide transparency window from 380 to 1800 nm thus confirming the suitability of this material for optical applications. The powder second harmonic generation efficiency of GuNB is about 3.3 times that of KDP. The crystal exhibits high laser damage threshold, which is a favorable property for nonlinear optical applications. The Vicker’s microhardness values measured on the different planes of GuNB crystal indicate high mechanical strength and microhardness anisotropy. References [1] M. Kitazawa, R. Higuchi, M. Takahashi, Applied Physics Letters 64 (1994) 2477. [2] W.S. Wang, M.D. Aggarwal, J. Choi, T. Gebre, A.D. Shields, B.G. Penn, D.O. Frazier, Journal of Crystal Growth 198 (1999) 578. [3] J.P. Jasinski, R.J. Butcher, M.T. Swamy, H.S. Yathirajan, A.R. Ramesha, Acta Crystallographica E 65 (2009) o2788. ¨ ¨ [4] W. Krumbe, S. Haussuhl, R. Frohlich, Zeitschrift fur Kristallographie 187 (1989) 309. [5] Zorka Machova, Ivan Nemec, Karel Teubner, Petr Nemec, Premysl Vanek, Zdenk Micka, Journal of Molecular Structure 832 (2007) 101. [6] V. Siva shanker, R. Siddeswaran, T. Bharthasarathi, P. Murugakoothan, Journal of Crystal Growth 311 (2009) 2709. [7] J.M. Adams, R.G. Pritchard, Journal of Applied Crystallography 8 (1975) 392. [8] M. Drozd, Spectrachimica Acta Part A 65 (2006) 1069. [9] X.M. Yang, D.A. Tryk, K. Hashimoto, A. Fujishima, Journal of Physical Chemistry B 102 (1998) 4933. [10] H.A. Petrosyan, H.A. Apetyan, A.M. Petrosyan, Journal of Molecular Structure 794 (2006) 160. [11] S.K. Kurtz, T.T. Perry, Journal of Applied Physics 39 (1968) 3798. [12] S. Vanishri, J.N. Babu Reddy, H.I. Bhat, S. GhoSh, Applied Physics B 88 (2007) 457. [13] S. Boomadevi, H.P. Mittal, R. Dhanasekaran, Journal of Crystal Growth 261 (2004) 55. [14] N. Vijayan, G. Bhagavannarayana, K.R. Ramesh, R. Gopalakrisnan, K.K. Maurya, P. Ramasamy, Crystal Growth and Design 6 (2006) 1542. [15] A. Bhaskaran, C.M. Ragavan, R. Sankar, R. Mohankumar, R. Jayavel, Crystal Research and Technology 42 (2007) 477. [16] M. Hanneeman, Metallurgia Manchu 23 (1941) 135.