- Email: [email protected]
Study on growth, spectral, optical and thermal characterization of an NLO crystal: 6-Methyl nicotinic acid (6MNA)
Optics & Laser Technology 90 (2017) 133–135
Contents lists available at ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
crossmark
Study on growth, spectral, optical and thermal characterization of an NLO crystal: 6-Methyl nicotinic acid (6MNA) S. Mary Delphinea, A.R.S. Janci Rani Julietb, S. Janarthananc, R. Sugaraj Samueld,
⁎
a
Department of Physics, Holy Cross College, Nagercoil, Tamil Nadu, India Department of Physics, Lady Doak College, Madurai, Tamil Nadu, India Department of Physics, Adhi College of Engineering and Technology, Kancheepuram, Tamil Nadu, India d Department of Physics, The New College, Chennai, Tamil Nadu, India b c
A R T I C L E I N F O
A BS T RAC T
Keywords: X-ray diffraction Growth from solutions Single crystal growth Nonlinear optical materials
6-methyl-nictinic acid (6MNA), organic non linear optical (NLO) single crystals were grown by slow evaporation solution technique. The cell parameters of 6MNA were confirmed from single crystal X-ray diffraction analysis. The Fourier transforms infrared and proton Nuclear magnetic resonance spectral analysis confirm the presence of various functional groups and the placement of protons respectively in 6MNA compound. UV–vis–NIR spectral studies revealed that the grown 6MNA has good optical transmission in the range of entire visible region. The thermal properties of crystals were evaluated from thermogravimetric (TG) and differential thermal analysis (DTA). It has shown that the grown crystals were stable up to 213°C. The second harmonic generation (SHG) measurements indicated that the efficiency of 6MNA is two times greater than that of the KDP crystals and is suitable for frequency conversion applications.
1. Introduction In the recent year, the nonlinear optical crystals, both organic and inorganic, with large second-order optical nonlinearities, attracted the materials scientists. These materials have a significant impact on optical communication, remote switching, laser technology and optical storage technology etc. In the few decades, many organic and inorganic materials have been developed to cover the possible applications in ultra-violet, near and far- infrared wavelength regions [1–3]. Great attention has been paid to organic NLO materials due to their promising applications in optoelectronics and the much larger nonlinear response, very fast switching time and convenient optimization routs through molecular engineering compared to the currently studied inorganic materials [4–6]. Many organic compounds show good NLO property due to the presence of π-bonds, which helps in the molecular engineering for the tailor made applications. With cascaded frequency conversions, deep UV coherent light can be produced in solid state lasers using NLO crystals. Large second order NLO response is possible in the molecule with various delocalization π electrons, since there will be a change in the dipole moment from ground state to keyed up state which will have large transition moment and noncentro symmetric response [7–9]. Recently, several investigations have been carried out on the
⁎
complexes of pyridine carboxylic acids, namely nicotinic, isonicotinic acid and picolinic acids. This has led to their use in various fields including electronics; for instance, in electroluminescent devices in analytic tools, functional biological assays and in medical imaging devices [10–12]. Single crystals are the backbone of the modern technological revolution. The impact of single crystals is clearly visible in industries that deal with semiconductors, laser technology etc. Most of the high performance. Optoelectronic devices are made from crystalline materials [13,14]. We report the results of our work on 6-methyl nicotinic acid (6MNA) single crystals right from the crystal growth by slow evaporation solution growth and various characterizations such as singly crystal XRD, spectral, optical, and thermal and powder SHG measurements. 2. Materials and methods 2.1. Crystal growth The commercially available 6-methyl- nictinic acid (6MNA) (AR grade) was purified by repeated crystallization process before growth as it would improve the purity of the material, which in turn would enhance the optical quality of the crystals. As the growth process and the quality of the crystals significantly depend on super saturation, the
Corresponding author. E-mail address: [email protected] (R.S. Samuel).
http://dx.doi.org/10.1016/j.optlastec.2016.11.013 Received 1 August 2016; Received in revised form 7 November 2016; Accepted 14 November 2016 0030-3992/ © 2016 Elsevier Ltd. All rights reserved.
Optics & Laser Technology 90 (2017) 133–135
S.M. Delphine et al.
Fig. 1. As grown crystal of 6MNA.
solution was prepared. 6MNA crystals were grown by temperature lowering method. The solution of recrystallized 6MNA was prepared at 30 °C using methanol as a solvent. The beaker containing the solution was covered and the solution was housed in a constant temperature bath ( ± 0.1 °C) and continuously stirred using Teflon coated immiscible magnetic stirrer. Utmost care was taken towards maintenance of temperature because even minor fluctuations in temperature would lead to inclusion of defects in the growing crystals. The temperature was lowered at a rate of 0.5 °C day−1. After 32 days, transparent crystals were obtained as shown in Fig. 1. A large size crystal can be obtained by taking large quantity of the starting material.
Fig. 3. FTIR spectrum of 6MNA.
stretching vibration of CH3 group. The peaks at 2964 cm−1 and 2950 cm−1 are due to symmetric stretching vibrations. The methyl bending mode is assigned at 1367 cm−1. The strong band at 1750 cm−1 is due to C˭O stretching vibration of carboxylic group. The other strong band observed at 1083 cm−1 is due to C-O stretching vibration. The CN stretching as mixed modes are assigned at 1283 cm−1. 3.3. 1H NMR spectral analysis The NMR spectral analysis is the important analytical technique used for the study on the structure of organic compounds. In the present investigation also, the 1H NMR spectrums was recorded to confirm the molecular structure of 6MNA. The 1H NMR spectrum of 6MNA, was recorded on a Varian XL −200 spectrometer operating at 200 MHz using deuterated methanol as solvent. The spectrum is shown in Fig. 4. A singlet at 8.7 ppm corresponds to a proton between the pyridine nitrogen and carboxylic acid. The doublet appeared at 7.8 ppm is due to proton ortho to the –COOH group. The doublet at 7.2 ppm can be attributed to the proton ortho to the methyl group. The methyl group appeared as a singlet at 2.4 ppm.
3. Results and discussion 3.1. X-ray diffraction study The structure of 6MNA crystal was examined by single crystal XRD analysis and the lattice parameters values were determined using Enraf Nonius CAD4 diffractometer with an incident MoKα radiation. It was found that the grown 6MNA crystal belongs to monoclinic system with space group P21 whose a=3.732 Å, b=6.401 Å, c=13.541 Å, α=γ=90°, β=90.53° and Volume, V=323.474 (Å)3. The results show good agreement with the reported values [15]. The powder sample of 6MNA was scanned over the range 10–60° at a rate of 1° per min. using a Rich Seifert Powder X-ray diffractometer with Cukα (1.54289 Å) radiation. The obtained XRD pattern was analyzed using PROSZKI software package and the diffraction peaks are indexed (Fig. 2).
3.4. UV–Vis–NIR spectral analysis The UV–Vis NIR spectrum occurs due to the electronic transitions in the molecule. This is a characteristic peak of a compound. The absorption spectrum of 6MNA was recorded using CARY 5E UV–vis– NIR Spectrophotometer in the region 200–900 nm. The spectrum is displayed in Fig. 5. It is observed that 6MNA is transparent in the entire visible region and the absorption takes place in the UV range between 228 and 267 nm. The at most absorption takes place at a wavelength of 228 nm. The lower cutoff wavelength of 6MNA was found to be 228 nm. The crystal has good optical transmission in the visible region. The transparency of crystal the visible region suggests that it is suitable for second harmonic generation.
3.2. FTIR spectral analysis The Fourier transform infrared (FTIR) analysis is an important study to identify with the various functional groups and structure of the compound. The FTIR spectrum was recorded using BRUKER IFS 66 V spectrometer in the wavelength range 4000–400 cm−1 by KBr pellet technique. FTIR spectrum of 6MNA is shown in Fig. 3. The OH - strong band appeared at 3567 cm−1. The bands at 1317 cm−1 and 1166 cm−1 are due to H-O-C bending respectively as mixed modes. The weak peaks at 3000 cm−1 and 2983 cm−1 are attributed to asymmetric
3.5. Thermal analysis The thermogravimetric analysis of 6MNA was carried out at a heating rate of 10 °C min −1 in the nitrogen atmosphere. The powdered
Fig. 4. 1H NMR spectrum of 6MNA.
Fig. 2. PXRD data of 6MNA.
134
Optics & Laser Technology 90 (2017) 133–135
S.M. Delphine et al.
successfully grown by slow evaporation solution growth technique. The grown crystal was characterized by single crystal XRD analysis. The various functional groups in 6MNA crystal were identified using FTIR and 1H NMR spectral analysis. The UV–VIS– NIR spectral analysis showed good transparency in the UV and visible region. Based on these observations we can say that 6MNA can be a promising novel NLO material, which can be possibly used for photonic application. It is observed from TGA- DTA studies that there is no phase transition in the grown material and is stable up to 212 ◦C. The SHG relative efficiency of 6MNA single crystal was found to be 2 times higher than that of KDP. Acknowledgements The authors are thankful to Dr. M. Vanjinathan, Assistant Professor in Chemistry, D.G. Vaishnav College and Chennai, India for his help in the spectral analyses and interpretations.
Fig. 5. UV–Vis–NIR spectrum of 6MNA.
References [1] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals 1 & 2, Academic Press, New York, 1987. [2] J. Badan, R. Hierle, A. Perigaud, J. Zyss, D.J. Wil-liams, Nonlinear Optical Properties of Organic Molecules and Polymeric Materials 233, American Chemical Society, Washington, DC, 1993 (American Chemical Symposium Series). [3] D. Balasubramanian, R. Jayavel, P. Murugakoothan, Studies on the growth aspects of organic L-alanine maleate: a promising nonlinear optical crystal, Nat. Sci. 1 (3) (2009) 216–221. [4] P. Vinothkumar, R. Mohan Kumar, R. Jayavel, A. Bhaskaran, Synthesis, growth, structural, optical, thermal and mechanical properties of an organic urea maleic acid single crystals for nonlinear optical applications, Opt. Laser Technol. 81 (2016) 145–152. [5] K. Selvaraju, K. Kirubavathi, S. Kumararaman, Growth and characterization of a new semi-organic nonlinear optical crystal: thiosemicarbazide cadmium acetate, J. Miner. Mater. Charact. Eng. 11 (3) (2012) 303–310. [6] Takao Tomono, Potential of P1 organic crystal for compact SHG green laser, Opt. Laser Technol. 68 (2015) 220–224. [7] Pai Shan, Tongqing Sun, Hong Chen, Hongde Liu, Shaolin Chen, Liu Xuanwen, Yongfa Kong, Jingjun Xu, Crystal growth and optical characteristics of berylliumfree polyphosphate, KLa(PO3)4, a possible deep-ultraviolet nonlinear optical crystal (article number: 25201)Sci. Rep. 6 (2016) (article number: 25201). [8] A.E. Whitten, P. Turner, W.T. Klooster, R.O. Piltz, M.A. Spackman, Reassessment of large dipole moment enhancements in crystals: a detailed experimental and theoretical charge density analysis of 2-methyl-4-nitroaniline, J. Phys. Chem. A 110 (2006) 8763–8776. [9] T. Zhou, C.E. Dykstra, Additivity and transferability of atomic contributions to molecular second dipole Hyperpolarizabilities, J. Phys. Chem. A 104 (2000) 2204–2210. [10] R.D. Rajasekhar, R. Laura, E. Pedro, M. Lawrence, Luminescent trimethoprimpolyaminocarboxylate lanthanide complex conjugates for selective protein labeling and time-resolved bioassays, Bioconjugate Chem. 22 (2011) 1402–1409. [11] J. Hongfei, W. Guilan, Z. Wenzhu, L. Xiaoyu, Y. Zhiqiang, J. Dayong, Y. Jingli, L. Zhiguang, J. Fluoresc, Preparation and time-resolved luminescence bioassay application of multicolor luminescent lanthanide nanoparticles, J. Fluoresc. 20 (2010) 321–328. [12] S. Faulkner, S.J.A. Pope, B.P. Burton-Pye, Lanthanide complexes for luminescence imaging applications, Appl. Spectrosc. Rev. 40 (2005) 1–39. [13] C. Krishnan, P. Selvarajan, S. Pari, Synthesis, growth and studies of undoped and sodium chloride doped zinc tris-thiourea sulphate (ZTS) single crystals, Curr. Appl. Phys. 10 (2010) 664–669. [14] V. Chithambaram, S. Krishnan, Synthesis, optical and thermal studies on novel semi organic nonlinear optical urea zinc acetate crystals by solution growth technique for the applications of optoelectronic devices, Opt. Laser Technol. 55 (2014) 18–20. [15] Mei-Ling Pan, Yang-Hui Luo, Shu-Lin Mao, 6-Methylnicotinic acid, Acta Crystallogr. 67 (2011) o2345. [16] S.K. Kurtz, T.T. Perry, Powder technique for the evaluation of nonlinear optical materials, J. Appl Phys. 39 (1968) 3798–3813.
Fig. 6. TG/DTA curves of 6MNA.
sample of about 9 mg of 6MNA crystal was used for the analysis. The TG trace is illustrated in Fig. 6. There is a weight loss at 213 °C, which indicates the sublime nature of the crystal. Hence, for any application, the crystal can be used up to 213 °C. The result of DTA shows a sharp endothermic peak at 213 °C. The sharp endothermic starts just below 212.9 °C and it coincides with the sublimation temperature as noted in TG. 3.6. NLO study The second harmonic generation (SHG) behavior of 6MNA crystal was observed by Kurtz-Perry powder technique [16]. It was observed by illuminating 6MNA crystal using Spectra Physics Quanta Ray GCR-2 Nd: YAG laser with the first harmonic output of 1064 nm, a pulse width of 8 ns and pulse energy of up to 300 mJ. The beam was well focused before it was incident on the crystal. The second harmonic signal generated in the crystal was confirmed from a strong bright green emission emerging from the 6MNA crystal which showed that the sample exhibited good NLO property. The second harmonic generation efficiency has been found to be comparable to phase matched KDP crystal. It is observed that the conversion efficiency of 6MNA is two times that of KDP crystal. 4. Conclusion The good quality single crystal of 6-methyl nicotinic acid was
135
Contents lists available at ScienceDirect
Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec
crossmark
Study on growth, spectral, optical and thermal characterization of an NLO crystal: 6-Methyl nicotinic acid (6MNA) S. Mary Delphinea, A.R.S. Janci Rani Julietb, S. Janarthananc, R. Sugaraj Samueld,
⁎
a
Department of Physics, Holy Cross College, Nagercoil, Tamil Nadu, India Department of Physics, Lady Doak College, Madurai, Tamil Nadu, India Department of Physics, Adhi College of Engineering and Technology, Kancheepuram, Tamil Nadu, India d Department of Physics, The New College, Chennai, Tamil Nadu, India b c
A R T I C L E I N F O
A BS T RAC T
Keywords: X-ray diffraction Growth from solutions Single crystal growth Nonlinear optical materials
6-methyl-nictinic acid (6MNA), organic non linear optical (NLO) single crystals were grown by slow evaporation solution technique. The cell parameters of 6MNA were confirmed from single crystal X-ray diffraction analysis. The Fourier transforms infrared and proton Nuclear magnetic resonance spectral analysis confirm the presence of various functional groups and the placement of protons respectively in 6MNA compound. UV–vis–NIR spectral studies revealed that the grown 6MNA has good optical transmission in the range of entire visible region. The thermal properties of crystals were evaluated from thermogravimetric (TG) and differential thermal analysis (DTA). It has shown that the grown crystals were stable up to 213°C. The second harmonic generation (SHG) measurements indicated that the efficiency of 6MNA is two times greater than that of the KDP crystals and is suitable for frequency conversion applications.
1. Introduction In the recent year, the nonlinear optical crystals, both organic and inorganic, with large second-order optical nonlinearities, attracted the materials scientists. These materials have a significant impact on optical communication, remote switching, laser technology and optical storage technology etc. In the few decades, many organic and inorganic materials have been developed to cover the possible applications in ultra-violet, near and far- infrared wavelength regions [1–3]. Great attention has been paid to organic NLO materials due to their promising applications in optoelectronics and the much larger nonlinear response, very fast switching time and convenient optimization routs through molecular engineering compared to the currently studied inorganic materials [4–6]. Many organic compounds show good NLO property due to the presence of π-bonds, which helps in the molecular engineering for the tailor made applications. With cascaded frequency conversions, deep UV coherent light can be produced in solid state lasers using NLO crystals. Large second order NLO response is possible in the molecule with various delocalization π electrons, since there will be a change in the dipole moment from ground state to keyed up state which will have large transition moment and noncentro symmetric response [7–9]. Recently, several investigations have been carried out on the
⁎
complexes of pyridine carboxylic acids, namely nicotinic, isonicotinic acid and picolinic acids. This has led to their use in various fields including electronics; for instance, in electroluminescent devices in analytic tools, functional biological assays and in medical imaging devices [10–12]. Single crystals are the backbone of the modern technological revolution. The impact of single crystals is clearly visible in industries that deal with semiconductors, laser technology etc. Most of the high performance. Optoelectronic devices are made from crystalline materials [13,14]. We report the results of our work on 6-methyl nicotinic acid (6MNA) single crystals right from the crystal growth by slow evaporation solution growth and various characterizations such as singly crystal XRD, spectral, optical, and thermal and powder SHG measurements. 2. Materials and methods 2.1. Crystal growth The commercially available 6-methyl- nictinic acid (6MNA) (AR grade) was purified by repeated crystallization process before growth as it would improve the purity of the material, which in turn would enhance the optical quality of the crystals. As the growth process and the quality of the crystals significantly depend on super saturation, the
Corresponding author. E-mail address: [email protected] (R.S. Samuel).
http://dx.doi.org/10.1016/j.optlastec.2016.11.013 Received 1 August 2016; Received in revised form 7 November 2016; Accepted 14 November 2016 0030-3992/ © 2016 Elsevier Ltd. All rights reserved.
Optics & Laser Technology 90 (2017) 133–135
S.M. Delphine et al.
Fig. 1. As grown crystal of 6MNA.
solution was prepared. 6MNA crystals were grown by temperature lowering method. The solution of recrystallized 6MNA was prepared at 30 °C using methanol as a solvent. The beaker containing the solution was covered and the solution was housed in a constant temperature bath ( ± 0.1 °C) and continuously stirred using Teflon coated immiscible magnetic stirrer. Utmost care was taken towards maintenance of temperature because even minor fluctuations in temperature would lead to inclusion of defects in the growing crystals. The temperature was lowered at a rate of 0.5 °C day−1. After 32 days, transparent crystals were obtained as shown in Fig. 1. A large size crystal can be obtained by taking large quantity of the starting material.
Fig. 3. FTIR spectrum of 6MNA.
stretching vibration of CH3 group. The peaks at 2964 cm−1 and 2950 cm−1 are due to symmetric stretching vibrations. The methyl bending mode is assigned at 1367 cm−1. The strong band at 1750 cm−1 is due to C˭O stretching vibration of carboxylic group. The other strong band observed at 1083 cm−1 is due to C-O stretching vibration. The CN stretching as mixed modes are assigned at 1283 cm−1. 3.3. 1H NMR spectral analysis The NMR spectral analysis is the important analytical technique used for the study on the structure of organic compounds. In the present investigation also, the 1H NMR spectrums was recorded to confirm the molecular structure of 6MNA. The 1H NMR spectrum of 6MNA, was recorded on a Varian XL −200 spectrometer operating at 200 MHz using deuterated methanol as solvent. The spectrum is shown in Fig. 4. A singlet at 8.7 ppm corresponds to a proton between the pyridine nitrogen and carboxylic acid. The doublet appeared at 7.8 ppm is due to proton ortho to the –COOH group. The doublet at 7.2 ppm can be attributed to the proton ortho to the methyl group. The methyl group appeared as a singlet at 2.4 ppm.
3. Results and discussion 3.1. X-ray diffraction study The structure of 6MNA crystal was examined by single crystal XRD analysis and the lattice parameters values were determined using Enraf Nonius CAD4 diffractometer with an incident MoKα radiation. It was found that the grown 6MNA crystal belongs to monoclinic system with space group P21 whose a=3.732 Å, b=6.401 Å, c=13.541 Å, α=γ=90°, β=90.53° and Volume, V=323.474 (Å)3. The results show good agreement with the reported values [15]. The powder sample of 6MNA was scanned over the range 10–60° at a rate of 1° per min. using a Rich Seifert Powder X-ray diffractometer with Cukα (1.54289 Å) radiation. The obtained XRD pattern was analyzed using PROSZKI software package and the diffraction peaks are indexed (Fig. 2).
3.4. UV–Vis–NIR spectral analysis The UV–Vis NIR spectrum occurs due to the electronic transitions in the molecule. This is a characteristic peak of a compound. The absorption spectrum of 6MNA was recorded using CARY 5E UV–vis– NIR Spectrophotometer in the region 200–900 nm. The spectrum is displayed in Fig. 5. It is observed that 6MNA is transparent in the entire visible region and the absorption takes place in the UV range between 228 and 267 nm. The at most absorption takes place at a wavelength of 228 nm. The lower cutoff wavelength of 6MNA was found to be 228 nm. The crystal has good optical transmission in the visible region. The transparency of crystal the visible region suggests that it is suitable for second harmonic generation.
3.2. FTIR spectral analysis The Fourier transform infrared (FTIR) analysis is an important study to identify with the various functional groups and structure of the compound. The FTIR spectrum was recorded using BRUKER IFS 66 V spectrometer in the wavelength range 4000–400 cm−1 by KBr pellet technique. FTIR spectrum of 6MNA is shown in Fig. 3. The OH - strong band appeared at 3567 cm−1. The bands at 1317 cm−1 and 1166 cm−1 are due to H-O-C bending respectively as mixed modes. The weak peaks at 3000 cm−1 and 2983 cm−1 are attributed to asymmetric
3.5. Thermal analysis The thermogravimetric analysis of 6MNA was carried out at a heating rate of 10 °C min −1 in the nitrogen atmosphere. The powdered
Fig. 4. 1H NMR spectrum of 6MNA.
Fig. 2. PXRD data of 6MNA.
134
Optics & Laser Technology 90 (2017) 133–135
S.M. Delphine et al.
successfully grown by slow evaporation solution growth technique. The grown crystal was characterized by single crystal XRD analysis. The various functional groups in 6MNA crystal were identified using FTIR and 1H NMR spectral analysis. The UV–VIS– NIR spectral analysis showed good transparency in the UV and visible region. Based on these observations we can say that 6MNA can be a promising novel NLO material, which can be possibly used for photonic application. It is observed from TGA- DTA studies that there is no phase transition in the grown material and is stable up to 212 ◦C. The SHG relative efficiency of 6MNA single crystal was found to be 2 times higher than that of KDP. Acknowledgements The authors are thankful to Dr. M. Vanjinathan, Assistant Professor in Chemistry, D.G. Vaishnav College and Chennai, India for his help in the spectral analyses and interpretations.
Fig. 5. UV–Vis–NIR spectrum of 6MNA.
References [1] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals 1 & 2, Academic Press, New York, 1987. [2] J. Badan, R. Hierle, A. Perigaud, J. Zyss, D.J. Wil-liams, Nonlinear Optical Properties of Organic Molecules and Polymeric Materials 233, American Chemical Society, Washington, DC, 1993 (American Chemical Symposium Series). [3] D. Balasubramanian, R. Jayavel, P. Murugakoothan, Studies on the growth aspects of organic L-alanine maleate: a promising nonlinear optical crystal, Nat. Sci. 1 (3) (2009) 216–221. [4] P. Vinothkumar, R. Mohan Kumar, R. Jayavel, A. Bhaskaran, Synthesis, growth, structural, optical, thermal and mechanical properties of an organic urea maleic acid single crystals for nonlinear optical applications, Opt. Laser Technol. 81 (2016) 145–152. [5] K. Selvaraju, K. Kirubavathi, S. Kumararaman, Growth and characterization of a new semi-organic nonlinear optical crystal: thiosemicarbazide cadmium acetate, J. Miner. Mater. Charact. Eng. 11 (3) (2012) 303–310. [6] Takao Tomono, Potential of P1 organic crystal for compact SHG green laser, Opt. Laser Technol. 68 (2015) 220–224. [7] Pai Shan, Tongqing Sun, Hong Chen, Hongde Liu, Shaolin Chen, Liu Xuanwen, Yongfa Kong, Jingjun Xu, Crystal growth and optical characteristics of berylliumfree polyphosphate, KLa(PO3)4, a possible deep-ultraviolet nonlinear optical crystal (article number: 25201)Sci. Rep. 6 (2016) (article number: 25201). [8] A.E. Whitten, P. Turner, W.T. Klooster, R.O. Piltz, M.A. Spackman, Reassessment of large dipole moment enhancements in crystals: a detailed experimental and theoretical charge density analysis of 2-methyl-4-nitroaniline, J. Phys. Chem. A 110 (2006) 8763–8776. [9] T. Zhou, C.E. Dykstra, Additivity and transferability of atomic contributions to molecular second dipole Hyperpolarizabilities, J. Phys. Chem. A 104 (2000) 2204–2210. [10] R.D. Rajasekhar, R. Laura, E. Pedro, M. Lawrence, Luminescent trimethoprimpolyaminocarboxylate lanthanide complex conjugates for selective protein labeling and time-resolved bioassays, Bioconjugate Chem. 22 (2011) 1402–1409. [11] J. Hongfei, W. Guilan, Z. Wenzhu, L. Xiaoyu, Y. Zhiqiang, J. Dayong, Y. Jingli, L. Zhiguang, J. Fluoresc, Preparation and time-resolved luminescence bioassay application of multicolor luminescent lanthanide nanoparticles, J. Fluoresc. 20 (2010) 321–328. [12] S. Faulkner, S.J.A. Pope, B.P. Burton-Pye, Lanthanide complexes for luminescence imaging applications, Appl. Spectrosc. Rev. 40 (2005) 1–39. [13] C. Krishnan, P. Selvarajan, S. Pari, Synthesis, growth and studies of undoped and sodium chloride doped zinc tris-thiourea sulphate (ZTS) single crystals, Curr. Appl. Phys. 10 (2010) 664–669. [14] V. Chithambaram, S. Krishnan, Synthesis, optical and thermal studies on novel semi organic nonlinear optical urea zinc acetate crystals by solution growth technique for the applications of optoelectronic devices, Opt. Laser Technol. 55 (2014) 18–20. [15] Mei-Ling Pan, Yang-Hui Luo, Shu-Lin Mao, 6-Methylnicotinic acid, Acta Crystallogr. 67 (2011) o2345. [16] S.K. Kurtz, T.T. Perry, Powder technique for the evaluation of nonlinear optical materials, J. Appl Phys. 39 (1968) 3798–3813.
Fig. 6. TG/DTA curves of 6MNA.
sample of about 9 mg of 6MNA crystal was used for the analysis. The TG trace is illustrated in Fig. 6. There is a weight loss at 213 °C, which indicates the sublime nature of the crystal. Hence, for any application, the crystal can be used up to 213 °C. The result of DTA shows a sharp endothermic peak at 213 °C. The sharp endothermic starts just below 212.9 °C and it coincides with the sublimation temperature as noted in TG. 3.6. NLO study The second harmonic generation (SHG) behavior of 6MNA crystal was observed by Kurtz-Perry powder technique [16]. It was observed by illuminating 6MNA crystal using Spectra Physics Quanta Ray GCR-2 Nd: YAG laser with the first harmonic output of 1064 nm, a pulse width of 8 ns and pulse energy of up to 300 mJ. The beam was well focused before it was incident on the crystal. The second harmonic signal generated in the crystal was confirmed from a strong bright green emission emerging from the 6MNA crystal which showed that the sample exhibited good NLO property. The second harmonic generation efficiency has been found to be comparable to phase matched KDP crystal. It is observed that the conversion efficiency of 6MNA is two times that of KDP crystal. 4. Conclusion The good quality single crystal of 6-methyl nicotinic acid was
135