Optical, structural, thermal and powder SHG investigations on 5-chlorosalicylaldehyde single crystals

Optik 126 (2015) 3516–3521

Contents lists available at ScienceDirect

Optik journal homepage: www.elsevier.de/ijleo

Optical, structural, thermal and powder SHG investigations on 5-chlorosalicylaldehyde single crystals B. Babu a,b , J. Chandrasekaran a,∗ , R. Karunathan c , R. Sathyanarayanamoorthi c a b c

Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore 641 020, Tamil Nadu, India Department of Science and Humanities, Sri Krishna College of Engineering and Technology, Coimbatore 641 008, Tamil Nadu, India Department of Physics, PSG College of Arts and Science, Coimbatore 641 014, Tamil Nadu, India

a r t i c l e

i n f o

Article history: Received 15 September 2014 Accepted 30 August 2015 Keywords: Crystal growth Thermal analysis Nonlinear optical materials

a b s t r a c t Organic single crystals of 5-chlorosalicylaldehyde were grown by slow evaporation solution growth technique at room temperature. The crystal structure was analyzed by single crystal XRD and the title compound crystallizes in monoclinic system. Optical transmission studies were also carried out for the crystals. TG/DSC and photoconductivity studies were also taken for the grown crystals. The powder second harmonic generation efficiency of the crystal was tested using modified Kurtz and Perry technique and is about 2.66 times of KDP. In addition, theoretical first order hyperpolarizability and HOMO-LUMO properties were also performed for the crystal by using density functional theory. © 2015 Elsevier GmbH. All rights reserved.

1. Introduction In recent years nonlinear optics (NLO) is the forefront current research in the world. It plays a tremendous role in the emerging technology of photonics in this century. The nonlinear optical process providing the key functions of NLO materials for the second harmonic generation received consistent attention for applications in the field of frequency conversion, electro optic modulation, optical disk data storage, THz wave generation, optical switching, telecommunications, optical computing and optical information processing, laser fusion reaction, laser remote sensing, color display, medical diagnostics [1–5]. The solution growth of crystals is an important process used in many applications from the laboratory to the industry. Although serious efforts in the field had been made during the last two decades, researchers are still trying to find new effective nonlinear optical materials with higher efficiency. Many organic, semi organic and inorganic materials have been developed to satisfy current technological needs [6–11]. But organic NLO materials have been of particular interest large electronic susceptibility and inherent ultrafast response time, potential to create large devices, also they can have higher flexibility owing to greater possibilities for twisting in the molecular structure and exhibit very high laser damage threshold, because they are formed by weak Van der Waals and hydrogen bonds. Hence they possess a high degree of delocalization [12–19]. 5-chlorosalicylaldehyde

∗ Corresponding author. Tel.: +91 422 2692461; fax: +91 422 2692676. E-mail address: [email protected] (J. Chandrasekaran). http://dx.doi.org/10.1016/j.ijleo.2015.08.232 0030-4026/© 2015 Elsevier GmbH. All rights reserved.

is an organic material that exhibits an unusual crystal structure with both intramolecular and intermolecular OH to CH O hydrogen bonding. Previously Alan Aiken et al. [20] studied the crystal structure of this compound. A detailed literature survey reveals that there are no other reports available on this material. So, we initiated investigation into the optical transmittance, photoconductivity, photoluminescence, TG/DSC, powder SHG. In addition to these studies theoretical HOMO-LUMO and first order hyperpolarizability properties of the 5-chlorosalicylaldehyde crystal were also investigated. 2. Experimental details 2.1. Crystal growth Commercially available 5-chlrosalicylaldehyde was purchased from Alfa aesar (99.99%) and used without further purification. The title compound was dissolved in acetone and stirred well about half an hour using a magnetic stirrer. The saturated solution was filtered twice using Whatman filter paper (No. 42 grade) and taken in a 100 ml beaker. To control the evaporation of the solvent the beaker was covered with thin plastic paper and kept undisturbed for crystallization. After a week good quality crystals were harvested from the mother solution. The quality of the crystal is depicted in Fig. 1. 2.2. Characterization techniques The unit cell parameters and the intensity data at 298 K for the title compound were obtained from Oxford Diffraction Xcalibur Gemini single crystal X-ray diffractometer using graphite

B. Babu et al. / Optik 126 (2015) 3516–3521

3517

Fig. 1. Grown crystals of 5-chlorosalicylaldehyde. Fig. 2. Powder XRD pattern of 5-chlorosalicylaldehyde.

˚ Powder X-ray monochromated Mo K␣ radiation ( = 0.71073 A). diffraction pattern for the grown crystal was carried out using RICH ˚ SIEFERT X-ray powder diffractometer using CuK␣ ( = 1.5405 A) radiation. Thermal studies were carried out using Q600 SDT and Q20 DSC instruments from room temperature to 800 ◦ C. The optical transmission spectrum of 5-chlorosalicylaldehyde was recorded using Perkin-Elmer lambda 35 spectrometer in the wavelength region between 200 nm and 1500 nm. A Q-switched Nd:YAG laser was used to study the powder SHG efficiency. The photoluminescence spectrum of the title compound was carried out using Perkin Elmer LS 55 Luminescence Spectrophotometer. Photoconductivity study was taken using Keithley 6517B electrometer at room temperature. The theoretical quantum chemical studies were performed at HF and DFT [B3LYP (Becke’s three-parameter (B3) exchange in conjunction with the Lee–Yang–Parr’s (LYP) correlation functional) methods with HF/6-311++G and B3LYP/6-31G basis sets using Gaussian 09 programme [21]. Gauss View 5.0 visualization program [22] has been employed to shape HOMO-LUMO orbitals.

3. Results and discussions 3.1. X-Ray diffraction analysis Single crystal XRD confirms that the grown crystal belongs to monoclinic system with non-centro symmetric space group P21 . The lattice parameter values are a (Å) = 3.8834(4), b (Å) = 5.6488(5), c (Å) = 15.1496(14), ˛ (◦ ) = 90.00, ˇ (◦ ) = 93.395(10),  (◦ ) = 90.00, V (Å3 ) = 331.75(5), Z = 2. These are in good agreement with the previous reported values, which are given in Table 1 [20]. The recorded powder XRD spectrum is shown in Fig. 2. The sample was scanned over the range of 5◦ to 80◦ . A well sharp intense peak at specific 2 angle confirms the crystalline nature of the crystal. Using TREOR 90 programme the h k l values were indexed.

3.2. Optical transmittance studies To find the suitability of the crystals for optical applications, optical transmittance studies were recorded for the grown crystals in the range from 200 to 1500 nm. Fig. 3 shows the recorded transmittance spectrum. It is concluded from the figure that the crystal is optically transparent in the UV–Vis–NIR region. In the ultraviolet region strong absorption is observed at 302 nm, which is assigned to n to ␲* transition. There is no other typical absorption in the entire visible and NIR region. A large optical transmittance window (360 nm to 1500 nm) with a maximum transparency of 76% is observed for the crystal. As a result, it can be utilized for SHG from a laser operating at 1064 nm or other optical application in the blue region, which makes it suitable for laser frequency doubling and related optoelectronic application [23,24]. 3.3. Frontier molecular orbital (FMO) analysis Highest occupied molecular orbital (HOMO) and lowest lying unoccupied molecular orbital (LUMO) are called as frontier molecular orbitals (FMOs). The FMO plays a major role in the optical and electrical properties as well as in the quantum chemistry. The HOMO (outermost orbital) represents the ability to act as an electron donor and directly related to the ionization potential whereas the LUMO acts as an electron acceptor and directly related to the electron affinity. The highest and second highest occupied MO’s (HOMO and HOMO − 1), the lowest and the second lowest unoccupied MO’s − (LUMO and LUMO + 1) were also calculated. The atoms occupied by more densities of HOMO should have stronger ability for detaching electrons, whereas the atom with

Table 1 Crystallographic data for 5-chlorosalicylaldehyde. Data

Ref. [10]

Present work

Formula Crystal system a (Å) b (Å) c (Å) ˇ (◦ ) V (Å3 ) Space group Z

C7 H5 ClO2 Monoclinic 3.883 5.648 15.149 109.47 322.1 P21 2

C7 H5 ClO2 Monoclinic 3.800 5.595 15.174 109.47 331.75 P21 2

Fig. 3. Optical transmittance spectrum of 5-chlorosalicylaldehyde.

3518

B. Babu et al. / Optik 126 (2015) 3516–3521

Fig. 5. Emission spectrum of 5-chlorosalicylaldehyde.

3.4. First order hyperpolarizability calculations The theoretical values of fundamental NLO properties of 5chlorosalicylaldehyde crystals were obtained using the Gaussian 09 programme package with B3LYP/6-31G basic set. Calculated parameters through finite field approach are listed in Table 3. The numerical values of NLO parameters were acquired by substituting the GAUSSIAN 09 output data in the following equations. The total static dipole moment,



Fig. 4. Atomic orbital composition of the frontier molecular orbital for 5chlorosalicylaldehyde. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

more occupation of LUMO should be easier to gain electron. For 5-chlorosalicylaldehyde, the highest occupied molecular orbital (HOMO) lying at 0.03309 eV, is a delocalized ␲ orbital. The HOMO − 1, lying −0.31771 eV below the HOMO, is a delocalized ␲ orbital over both the entire molecules. Although, the HOMO − 2, lying −0.34712 eV below the HOMO, respectively, are ␲ orbitals that localized in aromatic ring. Whereas, the lowest unoccupied molecular orbital (LUMO), lying at −0.20457 eV, is ␲* orbital that localized for the titled molecule. The LUMO + 1 and LUMO + 2 lying about −0.15006 and −0.12621 eV above the LUMO, it is also a ␲* that is similar to LUMO. The positive phase is red and the negative one is green (Fig. 4). It is clear from the figure that, while the HOMO is localized on approximately the whole molecule, LUMO is localized on the aromatic ring. The HOMO–LUMO energy gap of 5clorosalicylaldehyde was calculated at the HF/6-311++G(d,p) basis set method. The energy gap of HOMO–LUMO explains the eventual charge transfer interaction within the molecule, which influences the biological activity of the molecule. The HOMO → LUMO transition implies an electron density relocate to ring from chlorine and partially from ring. Table 2 represents the FMO properties of 5-chlorosalicylaldehyde (Fig. 5).

Table 2 Comparison of HOMO, LUMO, energy gaps, and related molecular properties of 5chlorosalicylaldehyde (eV). Molecular properties

HF/6-311++G(d,p)

EHOMO (eV) ELUMO (eV) Energy gap [EHOMO − ELUMO ] Ionization energy (IE) = −EHOMO Electron affinity (EA) = −ELUMO Global hardness () = 1/2 (EHOMO − ELUMO ) Electronic chemical potential () = 1/2 (EHOMO + ELUMO ) Global electrophilicity (ω) = 2 /2

0.03309 −0.20457 0.23766 −0.03309 0.20457 0.11883 −0.08574 0.03093

2x + 2y + 2z

=

(1)

where x ,y and x are dipole moments along x, y, z directions. This dipole moment is a major electronic property of a molecule, which results from nonhomogeneous distribution of charges on the various atoms in the molecule. Also it is mainly used to study the intermolecular interactions involving the Van der Waals type dipole–dipole forces. Intermolecular interactions will be much stronger for the bigger dipole moment. The mean polarizability ˛xx + ˛yy + ˛zz 3

˛o =

(2)

where ˛xx , ˛yy and ˛zz are the diagonal components of the polarizability tensor and the other components (˛xy ,˛yz ,˛xz ) are not required to obtain isotropic quantity The anisotropy of polarizability, 1 ˛ = √ 2



˛xx − ˛yy

2



+ ˛yy − ˛zz

2

+ (˛zz − ˛xx )2 + 6˛2xx

(3)

The first hyperpolarizability ˇi = ˇiii +

 1 ˇiji + ˇjij + ˇjji 3

(4)

i= / j

In the presence of the applied electric field, the first order hyperpolarizability is a third rank tensor that can be explained by a 3 × 3 matrix with 27 components. Kleinman symmetry reduced them as 10 components. The value of total polarizability and hyperpolarizability from the x, y and z components obtained from the Gaussian 09 output is given as ˇo =





ˇxxx + ˇxyy + ˇxzz

+ ˇzzz + ˇxxz + ˇyyz

2

2



+ ˇyyy + ˇxxy + ˇyzz

2 (5)

Since the values of polarizability and hyperpolarizability of Gaussian 09 outputs are reported in atomic units (a.u.), the calculated values have been converted into electrostatic units (esu).

B. Babu et al. / Optik 126 (2015) 3516–3521

3519

Table 3 Theoretical electric dipole moment and hyperpolarizability values of 5-chlorosalicylaldehyde. Dipole (Debye) x y z

Polarizability (a.u.) −0.67088998 0.736317888 0.850389634

˛xx ˛yy ˛zz ˛xy ˛xz ˛yz

The calculated values of , ˛o , ˛, ˇo for 5-chlorosalicylaldehyde crystals with B3LYP/6-31 G methods were 1.309740403 D, 74.089079 A˚ 3 , 250.616655 A˚ 3 and 27.1575624 × 10−30 cm−5 esu−1 , whereas for urea they were 1.9846 D, 2.7923 A˚ 3 , 7.9437 A˚ 3 and 0.8461 × 10−30 cm−5 esu−1 . Thus the mean polarizability and hyperpolarizability values are 26.53 and 32.09 times greater than those of urea. From the above results it is concluded that 5chlorosalicylaldehyde can be utilized for NLO applications.

Hyperpolarizability (a.u.) 128.307026 −0.65238374 94.6125963 −1.2684538 −57.7756110 81.8009977

ˇxxx ˇyyy ˇzzz ˇxyy ˇxxy ˇxxz ˇxzz ˇyzz ˇyyz ˇxyz

127.468858 −57.7756110 81.8009977 −78.8052403 35.0274030 0.803615121 54.2006863 7.10581335 −7.36149524 19.0161320

heated between 80 ◦ C and 150 ◦ C. The weight loss for this step is 70%. The weight loss is due to the removal of CO, CO2 , C2 H4 , HCl and some hydrocarbons. The residue left out at the end of the decomposition pattern is carbon. There are two endothermic peaks observed in the DSC thermogram. The endothermic peaks observed at 100 ◦ C and 146 ◦ C are due to the first stage decomposition of the compound. 3.7. Photoconductivity

3.5. Photoluminescence analysis Photoluminescence study is a non destructive tool to carry out the luminescence behavior of the material. Also the spectrum emitted by the radioactive recombination of photogenerated minority carriers is the straight way to calculate the energy gap. The emission spectrum was acquired at room temperature for the excitation wavelength of 300 nm in a solid phase with spectral resolution of 0.2 nm. Emission spectrum for the grown crystal is depicted in Fig. 4. The broad emission peak observed at 447 nm (8184,926 a.u.) is attributed to blue fluorescence emission. It may be due to the aromatic ring and its contribution to molecular association through Van der Waals force in the crystal [25]. It is noticed that emission intensity suddenly decreases after 447 nm. The strong PL emission indicates that the title compound can be used as a potential candidate for optoelectronic applications [26]. The direct band gap of the material was calculated using the wavelength to energy relations (h, c and ), where  is the wavelength of the fluorescence. The energy band gap was found to be 2.76 eV. 3.6. TG/DSC studies The TG-DSC thermogram of the crystal is shown in Fig. 6. The compound is heated from room temperature to 800 ◦ C under nitrogen atmosphere at a heating rate of 10 ◦ C/min. The compound is stable up to 80 ◦ C. Afterwards it decomposes into single stage when

Fig. 6. TG/DSC spectrum of 5-chlorosalicylaldehyde.

Photoconductivity measurements were recorded using Keithley electrometer (Model: 6517B) at room temperature. The input voltage was increased from 1 to 10 V. Silver paint was applied to the opposite faces for taking the measurement. The dark current was recorded when the sample was unexposed to any radiation. Then the sample was illuminated by radiation using a 100 W halogen lamp containing iodine vapour and tungsten filament. The resultant photocurrent was measured for the same applied voltage. The plot of the dark current versus photocurrent is depicted in Fig. 7. From the figure it is observed that both the dark current and the photocurrent linearly increase with applied voltage. Also the dark current is higher than the photocurrent. This phenomenon is called negative photoconductivity, which was explained by the Stock man model [27]. Reduction of charge carriers in the presence of radiation could be due to the trapping process and increase in carrier velocity given by the relation T = (vsN)−1 where v is the thermal velocity of the carrier, s is the capture cross-section of the recombination centre and N is the carrier concentration. As intense light falls on the sample, the charge carriers’ lifetime decreases. According to the Stockman model, the forbidden gap in the material contains two energy levels. The upper energy level is situated between the Fermi level and the conduction band.

Fig. 7. Photoconductivity response for 5-chlorosalicylaldehyde.

3520

B. Babu et al. / Optik 126 (2015) 3516–3521

transmittance in the UV–vis–NIR region. It also exhibited blue light emission behavior, when excited at 447 nm. Thermal studies indicate that there is no phase transition up to 100 ◦ C. Photoconductivity study reveals the negative photoconductivity nature of the grown crystal. The powder SHG efficiency of the crystal was confirmed using Nd:YAG laser and found to be 2.66 times greater than that of the KDP crystal. It also confirms the phase matching behavior of the title compound. The density functional theory explored the HOMO-LUMO and first order hyperpolarizability properties of 5-chlorosalicylaldehyde in a detail.

Acknowledgements

Fig. 8. Particle size dependence of SHG output.

The lower energy level is situated near the valence band. This state has high capture cross sections for electrons and holes. This state can also capture electrons from the conduction band and holes from the valance band. As a result the number of charge carriers decreases in the presence of radiation giving rise to negative photoconductivity [28]. 3.8. Powder SHG studies The powder second harmonic generation test is the initial screening of NLO materials. At very first in 1961 Franken and his team studied the SHG properties of the crystalline quartz crystal using ruby maser [29]. Again in 1964, Rieckhoff and Peticolas studied the SHG properties powdered amino acids using ruby laser [30]. In 1968, Kurtz and Perry studied and demonstrated the existence or absence of phase matching conditions that can be determined from the powder [31]. The increase of SHG intensities with increase in particle size and remaining effectively stable at particle sizes bigger than the coherence length confirm the phase matching behavior of the material [32–35]. Finely crushed powders of 5chlorosalicylaldehyde crystals were graded by standard sieves of size of 25 to 250 ␮m and closely packed in the separate micro capillary tube of uniform diameter (1.8 mm). A Q-switched mode locked Nd:YAG laser (DCR II) with a fundamental wavelength of 1064 nm was used as an optical source. The input pulse energy was measured using a power meter and it is 2.5 mJ. A laser beam of 1064 nm with pulse width of 8 ns and repetition rate of 10 Hz was made to fall normally on the sample. The transmitted fundamental wave was passed over a monochromator, which separates 532 nm (SHG signal) from 1064 nm. A BG-38 filter kept in the path also removes the residual 1064 nm radiation. The SHG output (green light emission) is finally detected by a photomultiplier tube (Hamamatsu R5109) and displayed on a storage oscilloscope (TDS 3052 B 500 MHz, Phosphor digital oscilloscope). Potassium dihydrogen phosphate was powdered into uniform size and used as a reference in SHG measurement. An SHG signal of 24 mV was obtained for the grown crystal while KDP conferred an SHG signal of 9 mV, which is 2.66 times greater than that of standard KDP (120 ␮m). Also Fig. 8 clearly indicates that SHG efficiency is rising with increase in particle size thus proving the phase matching property. 4. Conclusion Organic single crystals of 5-chlorosalicylaldehyde were grown by slow evaporation solution growth technique at room temperature. The single crystal XRD confirms that the grown crystal belongs to the monoclinic system. The grown crystal exhibits large

The authors gratefully acknowledge the financial support from the DST, Government of India, for the major research project (SB/EMEQ-293/2013).

References [1] M. Lakshmipriya, D. Rajan Babu, R. Ezhil Vizhi, Nucleation kinetics, growth, and optical properties of potassium pentaborate single crystals, Physica B: Condens. Matter 430 (2013) 6–9. [2] G. Pabitha, R. Dhanasekaran, Investigation on the linear and nonlinear optical properties of a metal organic complex – bis thiourea zinc acetate single crystal, Opt. Laser Technol. 50 (2013) 150–154. [3] B. Babu, J. Chandrasekaran, S. Balaprabhakaran, Growth, structural, spectral, optical and electrical properties of 2-aminophenol single crystals, Optik 125 (2014) 3005–3008. [4] G. Shanmugam, M.S. Belsley, D. Isakov, E. de Matos Gomes, K. Nehru, S. Brahadeeswaran, Spectroscopic, nonlinear optical and quantum chemical studies on 4 Pyrrolidinium p-Hydroxybenzoate – a phase matchable organic NLO crystal, Spectrochim. Acta A 114 (2013) 284–292. [5] F. Li, S. Pan, X. Hou, J. Yao, A novel nonlinear optical crystal Bi2 ZnOB2 O6 , Cryst. Growth Des. 9 (2009) 4091–4095. [6] N.P. Rajesh, V. Kannan, P. Santhana Raghavan, P. Ramasamy, C.W. Lan, Optical and microhardness studies of KDP crystals grown from aqueous solutions with organic additives, Mater. Lett. 52 (2002) 326–328. [7] T. Pal, T. Kar, G. Bocelli, L. Rigi, Synthesis, growth, and characterization of larginine acetate crystal: a potential NLO material, Cryst. Growth Des. 3 (2003) 13–16. [8] A. Kandasamy, R. Siddeswaran, P. Murugakoothan, P. Suresh Kumar, R. Mohan, Synthesis, growth, and characterization of l-proline cadmium chloride monohydrate (l-PCCM) crystals: a new nonlinear optical material, Cryst. Growth Des. 7 (2007) 183–186. [9] Z. Yang, M. Worle, L. Mutter, M. Jazbinsek, P. Gunter, Synthesis, crystal structure and second-order nonlinear optical properties of new stilbazolium salts, Cryst. Growth Des. 7 (2007) 83–86. [10] K. Jagannathan, S. Kalainathan, T. Gnanasekaran, N. Vijayan, G. Bhagavannarayana, Growth and characterization of the NLO crystal 4-dimethylaminoN-methyl-4-stilbazolium tosylate (DAST), Cryst. Growth Des. 7 (2007) 859–863. [11] C. Justin Raj, S. Jerome Das, Bulk growth and characterization of semiorganic nonlinear optical l-alanine cadmium chloride single crystal by modified Sankaranarayanan–Ramasamy method, Cryst. Growth Des. 8 (2008) 2729–2732. [12] V.G. Dmitreiv, G.G. Gurzadyan, D.N. Nicogosyan, Handbook of Nonlinear Optical Crystals, Springer-Verlag, New York, NY, 1999. [13] E. Ishow, C. Bellaiche, L. Bouteiller, K. Nakatani, J.A. Delaire, Versatile synthesis of small NLO-active molecules forming amorphous materials with spontaneous second-order NLO response, J. Am. Chem. Soc. 125 (2003) 15744– 15745. [14] L.R. Dalton, P.A. Sulliven, B.C. Olbricht, D.H. Bale, J. Takayesu, S. Hammond, H. Rommel, B.H. Robinson, Tutorials in Complex Photonic Media, SPIE, Bellingham, WA, 2007. [15] T. Chen, Z. Sun, C. Song, Y. Ge, J. Luo, W. Lin, M. Hong, Bulk crystal growth and optical and thermal properties of the nonlinear optical crystal l-histidinium-4nitrophenolate 4-nitrophenol (LHPP), Cryst. Growth Des. 12 (2012) 2673–2678. [16] V. Krishnakumar, M. Rajaboopathi, R. Nagalakshmi, Studies on vibrational, dielectric, mechanical and thermal properties of organic nonlinear optical cocrystal: 2,6-diaminopyridinium–4-nitrophenolate–4-nitrophenol, Physica B: Condens. Matter 407 (2012) 1119–1123. [17] J. Chandrasekaran, S. Balaprabhakaran, B. Babu, Growth, structural, spectral and optical studies on 2,4-dinitrophenol organic single crystal, Optik 124 (2013) 4296–4299. [18] J. Chandrasekaran, B. Babu, S. Balaprabhakaran, P. Ilayabarathi, P. Maadeswaran, Growth and characterization of 2-aminothiazole–3,5dinitrosalicylic acid complex, J. Opt. Elect. Adv. Mater. 6 (2012) 211–213.

B. Babu et al. / Optik 126 (2015) 3516–3521 [19] L. Guru Prasad, V. Krishnakumar, R. Nagalakshmi, Investigations on the physicochemical properties of 2,4-dinitrophenol: efficient organic nonlinear optical crystal for frequency doubling, Physica B: Condens. Matter 405 (2010) 1652–1657. [20] R. Alan Aiken, A.L.G. Gidlow, R.S. Ramsewak, A.M.Z. Slawin, The X-ray structure of 5-chlorosalicylaldehyde, J. Chem. Crystallogr. 43 (2013) 65–69. [21] J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, O. Nakai, T. Vreven, J.A. Montgomery, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09 Program, Revision C.01, Gaussian, Inc, Wallingford, CT, 2010. [22] R.I. Dennington, T. Keith, J. Millam, K. Eppinnett, W. Hovell, Gauss View Version 3.09, 2003. [23] S. Dhanuskodi, K. Vasantha, X-ray diffraction, spectroscopic and thermal studies on a potential semiorganic NLO material: lithium bis-l-malato borate, Spectrochim. Acta, A: Mol. Biomol. Spectrosc. 61 (2005) 1777–1782. [24] K. Kirubavathi, K. Selvaraju, R. Valluvan, N. Vijayan, S. Kumararaman, Synthesis, growth, structural, spectroscopic and optical studies of a new semiorganic nonlinear optical crystal: l-valine hydrochloride, Spectrochim. Acta, A: Mol. Biomol. Spectrosc. 69 (2008) 1283–1286.

3521

[25] F. Yogama, I. Vetha Potheher, M. Vimalan, R. Jeyasekaran, T. Rajesh Kumar, P. Sagayaraj, Growth and physicochemical properties of l-phenylalaninium maleate: a novel nonlinear optical crystal, Spectrochim. Acta, A: Mol. Biomol. Spectrosc. 95 (2012) 369–373. [26] M. Jose, R. Uthrakumar, A. Jeya Rajendran, S. Jerome Das, Optical and spectroscopic studies of potassium p-nitrophenolate dihydrate crystal for frequency doubling applications, Spectrochim. Acta, A: Mol. Biomol. Spectrosc. 86 (2012) 495–499. [27] V.N. Joshi, Photoconductivity, Marcel Dekker, New York, NY, 1990. [28] B. Babu, J. Chandrasekaran, S. Balaprabhakaran, P. Ilyabarathi, Optical, structural and electrical properties of pure and urea doped KDP crystals, Mater. Sci. Poland 31 (2013) 151–157. [29] P.A. Franken, A.E. Hill, C.W. Peters, G. Weinreich, Generation of optical harmonics, Phys. Rev. Lett. 7 (1961) 118–120. [30] K.E. Rieckhoff, W.L. Peticolas, Optical second harmonic generation in crystalline amino acids, Science 147 (1964) 610–611. [31] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical materials, J. Appl. Phys. 39 (1968) 3798–3815. [32] M. Kiguchi, M. Kato, M. Okunak, Y. Taniguchi, New method of measuring second harmonic generation efficiency using powder crystals, Appl. Phys. Lett. 60 (1992) 1933–1935. [33] R.L. Sutherland, Handbook of Nonlinear Optics, second ed., Dekker, New York, NY, 2003. [34] H.S. Nalwa, S. Miyata, Nonlinear Optics of Organic Molecules and Polymers, CRC Press, Tokyo, 2000. [35] I. Aramburu, J. Ortega, C.L. Folcia, J. Etxebarria, M.A. Illarramendi, T. Breczewski, Accurate determination of second order nonlinear optical coefficients from powder crystal monolayers, J. Appl. Phys. 109 (2011) 113105.