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Growth and characterization of a new metal-organic nonlinear optical bis (thiourea) cadmium zinc chloride single crystals
Spectrochimica Acta Part A 71 (2008) 1–4
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Review
Growth and characterization of a new metal-organic nonlinear optical bis (thiourea) cadmium zinc chloride single crystals K. Kirubavathi a , K. Selvaraju a , S. Kumararaman b,∗ a b
Department of Physics, Thanthai Hans Roever College, Perambalur 621212, Tamilnadu, India Department of Physics, Nehru Memorial College, Puthanampatti 621007, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 31 October 2007 Received in revised form 4 May 2008 Accepted 7 May 2008 Keywords: Growth from solution Metal-organic X-ray diffraction Nonlinear optical crystal IR spectrum
a b s t r a c t A new semiorganic nonlinear optical bis (thiourea) cadmium zinc chloride (BTCZC) crystal has been synthesized. BTCZC single crystals were grown from aqueous solution by slow evaporation technique. The solubility of BTCZC has been determined for various temperatures. Single crystal X-ray diffraction (XRD) study has been carried out to identify the lattice parameters. Fourier transform infrared (FTIR) studies confirm the various functional groups present in the grown crystal. The transmission and absorption spectra of this crystal show that the lower cut off wavelength lies at 260 nm. The thermal analyses confirmed that the crystal is stable upto 201 ◦ C. The nonlinear optical (NLO) property of the grown crystal has been confirmed by Kurtz-powder second harmonic generation (SHG) test. © 2008 Elsevier B.V. All rights reserved.
Contents 1. 2.
3. 4.
5.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Material synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Crystal growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Single crystal XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. FTIR studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. UV–vis studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Thermal studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5. Second harmonic generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction The rapid development of optical communication systems has led to the search for more efficient compounds for the processing of optical signals. It has always been an active part to search after and study novel nonlinear optical (NLO) material in the field
∗ Corresponding author.Tel.: +91 4327 2234227; fax: +91 4328 276344. E-mail addresses: [email protected], [email protected] (S. Kumararaman). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.05.017
1 2 2 2 2 2 2 2 2 3 3 3 3 3
of material studying during the past few decades. Since the theory of double-radical model (organic conjugated molecular groups are included in the distorted polyhedron of coordination complex) was brought up in 1987 [1]. Metal-organic coordination compounds as NLO materials have attracted much more attention for their high NLO coefficients, stable physico-chemical properties and better mechanical intension. With the guidance of this theory, many metal-organic coordination complexes of thiourea materials with good NLO effect have been designed and synthesized [2–8]. The metal-organic complexes of thiourea such as zinc thiourea chloride (ZTC) and bis thiourea cadmium chloride (BTCC) have already been studied [9,10].
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In this present investigation, a new metal-organic NLO crystal of bis (thiourea) cadmium zinc chloride (BTCZC) is reported for the first time and the grown crystals have been characterized by various characterization studies. 2. Experimental procedure 2.1. Material synthesis The BTCZC salt was synthesized using high purity cadmium chloride, zinc chloride and thiourea (AR grade) in the ratio of 0.5:0.5:2. The calculated amount of salt was dissolved in double distilled water at room temperature. This solution was heated and kept for slow evaporation to dryness at room temperature. BTCZC salt was synthesized according to the reaction: ZnCl2 + CdCl2 + 2[NH2 CSNH2 ] → ZnCd[NH2 CSNH2 ]2 [Cl2 ]2 The purity of synthesized salt was further increased by successive recrystallization process. 2.2. Solubility The solubility of BTCZC was determined for four different temperatures, 30, 35, 40 and 45 ◦ C by dissolving the solute in deionized water in an airtight container maintained at a constant temperature with stirring. After saturation was attained, the equilibrium concentration of the solute was analyzed gravimetrically. The same procedure was repeated and the solubility curve for different temperature was drawn. 2.3. Crystal growth In the present study, BTCZC crystals were grown by using slow evaporation technique. Recrystallized salt of BTCZC was taken as raw material. Saturated BTCZC solution was prepared at room temperature with water as solvent. BTCZC is found to have a positive gradient of solubility. The prepared solution was filtered with a microfilter. The pH of this solution is 5.0. The solution was taken in vessels and closed with perforated covers and kept in a dust-free atmosphere. The crystals were harvested when they attained an optimal size and shape. 3. Characterization The single crystal X-ray diffraction pattern of BTCZC crystal was carried out using ENRAF NONIUS CAD4 X-ray diffractometer and its lattice parameters were determined. Fourier transform infrared spectrum was recorded by the KBr pellet technique using a BRUKER 66 V FTIR spectrometer to confirm the vibrational structure of the crystalline compound with the range of wavenumber 400–4000 cm−1 . UV–vis spectrum was recorded in the range of 200–2000 nm using VARIAN CARY 5E spectrometer. Thermal behavior of the grown sample was studied by using STA 1500 thermal analyzer. The NLO property of BTCZC was tested by Kurtz powder SHG test using an Nd:YAG laser. 4. Results and discussion
Fig. 1. FTIR spectrum of BTCZC crystal.
revealed that the grown crystal belongs to orthorhombic sys˚ tem with space group P21 21 21 unit cell parameters a = 11.918 A, ˚ b = 6.821 A˚ and c = 13.114 A. 4.2. FTIR studies The Fourier transform infrared (FTIR) spectrum of BTCZC is shown in Fig. 1. The assignment of various internal modes observed in these FTIR spectra is given in the Table 1. The assignments correspond to various internal vibrations of thiourea. Crystal structure investigations of thiourea have established the coplanarity structure of C, N and S atoms in the molecule [11]. In BTCZC complex, there are two possibilities by which the coordination of cadmium and zinc with thiourea can occur. It may occur either through nitrogen or sulfur of thiourea. The bands observed in the 3000–3500 cm−1 region in the FTIR spectra, at 3197, 3282 and 3389 cm−1 are characteristics of NH2 asymmetric and symmetric stretching vibrations and are in agreement with other compounds containing thiourea molecule CS(NH2 )2 [12–15]. The strong band observed at 1616 cm−1 in the BTCZC complex correspond to a band at 1625 cm−1 of thiourea, which is attributed to the NH2 deformation vibration similar to those of some metal thiourea complexes [16]. The band at 1477 cm−1 assigned to the N–C–N stretching vibration in thiourea is shifted to 1493 cm−1 in the BTCZC complex. This shift may be due to the greater double bond character of the carbon-to-nitrogen bond on complex formation. The appearance of band 1435 cm−1 and 1396 cm−1 for BTCZC against the absorption of pure thiourea at 1414 cm−1 confirms the formation of coordination. Lower shift of Table 1 Assignment of FTIR Frequencies (cm−1 ) Thiourea
BTCZC
Assignment
3380 3279 3177 1617 1477
3389 3282 3197 1616 1493
N–H stretching vibration N–H stretching vibration O–H stretching vibration N–H bending vibration N–C–N stretching vibration
1414
1435 1396
NH2 rocking vibration C S stretching vibration
1082 730 487 457
1096 713 474 530
NH2 rocking vibration C S stretching vibration N–C–N bending vibration S–C–N stretching vibration
4.1. Single crystal XRD To determine the unit cell parameters, the grown crystals were subjected to single crystal X-ray diffraction studies using Enraf Nonius CAD4 single crystal X-ray diffractometer. The X-ray analysis
K. Kirubavathi et al. / Spectrochimica Acta Part A 71 (2008) 1–4
Fig. 2. Optical spectrum of BTCZC crystal.
C S stretching frequency (730 – 713 cm−1 ) confirms the formation of metal–sulfur coordination bond [17]. These observations suggest that the metal coordinate with thiourea through sulfur in BTCZC. 4.3. UV–vis studies The UV–vis optical absorption and transmittance spectral analyses of BTCZC single crystal were carried out between 200 and 2000 nm. The transmittance spectrum (Fig. 2) depicts the transparency of the crystal is closed to 68% at 260 nm. But around 260 nm, there is a sharp decrease in transmittance due to absorbance leading to electronic excitation in this region. The cut-off frequency is 260 nm. At the longer wavelength side, the crystal is highly transparent (70%) upto 1800 nm. The absence of absorption in this region between 300 and 1800 nm shows that this crystal could be used for optical window applications. The absorption spectrum (Fig. 2) illustrates that there is a less absorbance in the entire UV–vis region. The lower cut-off wavelength of the crystal was found to be 260 nm. 4.4. Thermal studies A powdered sample weighing 1.871 mg was used for the analyses. The analyses were carried out simultaneously in nitrogen at a heating rate of 20 ◦ C/min for a temperature range of 30–600 ◦ C
3
and its represented in Fig. 3. Quite interesting and important to be notices is the very good thermal stability of the material upto 201 ◦ C. Another important observation is that, there is no phase transition till the material melts and this enhances the temperature range for the utility of the crystal for NLO applications. The absence of water of crystallization in the molecular structure is indicated by the absence of the weight loss around 100 ◦ C. The DTA curve shows as endothermic peak at 201 ◦ C which corresponds to the melting point of the compound. The peak of the endothermic represents the temperature at which the melting terminates which corresponds to its melting point at 209 ◦ C. Ideally, the melting portion of the trace corresponds to a vertical line. The TG curve of this sample indicates that the sample is stable up to 207 ◦ C after this temperature, this sample undergoes appreciable weight loss. The change in weight loss confirms the decomposing nature of the sample. The sharpness of the endothermic peak shows good degree of crystallinity of the grown ingot. The endothermic peak at 247 ◦ C indicates a phase change from liquid to vapor state as evidence from the loss of weight in TG curve. 4.5. Second harmonic generation The second harmonic generation (SHG) test on the BTCZC crystal was performed by Kurtz powder SHG method [18]. The powdered sample of BTCZC crystal was illuminated using the fundamental beam of 1064 nm from Q-switched Nd:YAG laser. Pulse energy 4 mJ/pulse and pulse width of 10 ns and repetition rate of 10 Hz were used. The second harmonic signal generated in the crystalline sample was confirmed from the emission of green radiation of wavelength 532 nm collected a monochromator after separating the 1064 nm pump beam with an IR-blocking filter. A photo multiplier tube as used as detector. It is observed that the measured SHG efficiency of BTCZC crystal was 1.1 times that of potassium dihydrogen phosphate (KDP). 5. Conclusion Bis (thiourea) cadmium zinc chloride (BTCZC) single crystals were grown by slow solvent evaporation technique for the first time. The crystallinity of the grown crystal was confirmed by single crystal X-ray diffraction analysis. Various functional groups present in the grown crystal was identified by FTIR spectrum. The optical quality of the grown crystal was justified by optical transmission studies. Thermal stability of the grown crystal was studied by TG & DTA analyses. The powder SHG measurement shows the grown BTCZC crystal having 1.1 times higher NLO efficiency than KDP. References
Fig. 3. TG/DTA curve of BTCZC crystal.
[1] D. Xu, M.H. Jian, X.T. Tao, Z.S. Shao, J. Synth. Cryst. 16 (1987) 1 (in Chinese). [2] N. Zhang, M.H. Jian, D.R. Yuan, D. Xu, X.T. Tao, Z.S. Shao, J. Cryst. Growth 102 (1990) 581. [3] V. Venkataramanan, G. Dhanaraj, V.K. Wadhawan, J.N. Shrewood, H.L. Bhat, J. Cryst. Growth 154 (1995) 92. [4] P.M. Ushasree, R. Muralidharan, R. Jayavel, P. Ramasamy, J. Cryst. Growth 218 (2000) 365. [5] M. Quassaid, P. Becker, C. Carabatos Nedelec, Phys. Stat. Sol. (b) 207 (1998) 499. [6] H.O. Marcy, C.F. Warren, M.S. Webb, C.A. Ebbers, S.P. Velsko, G.C. Kennedy, G.C. Catella, Appl. Opt. 31 (1992) 5051. [7] K. Selvaraju, R. Valluvan, S. Kumararaman, Mater. Lett. 60 (2006) 3130. [8] K. Selvaraju, R. Valluvan, S. Kumararaman, Mater. Lett. 61 (2007) 751. [9] V. Venkataramanan, C.K. Subramanian, H.L. Bhat, J. Appl. Phys. 77 (1995) 6049. [10] R. Rajasekaran, P.M. Ushasree, R. Jayavel, P. Ramasamy, J. Cryst. Growth 229 (2001) 563. [11] G.D. Andreeti, L. Cavalca, A. Musatti, Acta Crystallogr. B24 (1968) 683. [12] V. Winterfeld, G.Z. Schaack, Phys. B 26 (1980) 303.
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[13] K.T. Kim, J.J. Kim, Ferroelectrics 105 (1990) 243. [14] V. Venkataramanan, M.R. Srinivasan, H.L. Bhat, J. Raman Spectrosc. 25 (1994) 805. [15] S. Abraham, G. Aruldhas, Spectrochim. Acta A 51 (1995) 79.
[16] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordinate Compounds, Wiley, New York, 1978. [17] K. Swaminathan, H.M.N.H. Irving, J. Inorg. Nucl. Chem. 26 (1964) 1291. [18] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Review
Growth and characterization of a new metal-organic nonlinear optical bis (thiourea) cadmium zinc chloride single crystals K. Kirubavathi a , K. Selvaraju a , S. Kumararaman b,∗ a b
Department of Physics, Thanthai Hans Roever College, Perambalur 621212, Tamilnadu, India Department of Physics, Nehru Memorial College, Puthanampatti 621007, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 31 October 2007 Received in revised form 4 May 2008 Accepted 7 May 2008 Keywords: Growth from solution Metal-organic X-ray diffraction Nonlinear optical crystal IR spectrum
a b s t r a c t A new semiorganic nonlinear optical bis (thiourea) cadmium zinc chloride (BTCZC) crystal has been synthesized. BTCZC single crystals were grown from aqueous solution by slow evaporation technique. The solubility of BTCZC has been determined for various temperatures. Single crystal X-ray diffraction (XRD) study has been carried out to identify the lattice parameters. Fourier transform infrared (FTIR) studies confirm the various functional groups present in the grown crystal. The transmission and absorption spectra of this crystal show that the lower cut off wavelength lies at 260 nm. The thermal analyses confirmed that the crystal is stable upto 201 ◦ C. The nonlinear optical (NLO) property of the grown crystal has been confirmed by Kurtz-powder second harmonic generation (SHG) test. © 2008 Elsevier B.V. All rights reserved.
Contents 1. 2.
3. 4.
5.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Material synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Crystal growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Single crystal XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. FTIR studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. UV–vis studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Thermal studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5. Second harmonic generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction The rapid development of optical communication systems has led to the search for more efficient compounds for the processing of optical signals. It has always been an active part to search after and study novel nonlinear optical (NLO) material in the field
∗ Corresponding author.Tel.: +91 4327 2234227; fax: +91 4328 276344. E-mail addresses: [email protected], [email protected] (S. Kumararaman). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.05.017
1 2 2 2 2 2 2 2 2 3 3 3 3 3
of material studying during the past few decades. Since the theory of double-radical model (organic conjugated molecular groups are included in the distorted polyhedron of coordination complex) was brought up in 1987 [1]. Metal-organic coordination compounds as NLO materials have attracted much more attention for their high NLO coefficients, stable physico-chemical properties and better mechanical intension. With the guidance of this theory, many metal-organic coordination complexes of thiourea materials with good NLO effect have been designed and synthesized [2–8]. The metal-organic complexes of thiourea such as zinc thiourea chloride (ZTC) and bis thiourea cadmium chloride (BTCC) have already been studied [9,10].
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In this present investigation, a new metal-organic NLO crystal of bis (thiourea) cadmium zinc chloride (BTCZC) is reported for the first time and the grown crystals have been characterized by various characterization studies. 2. Experimental procedure 2.1. Material synthesis The BTCZC salt was synthesized using high purity cadmium chloride, zinc chloride and thiourea (AR grade) in the ratio of 0.5:0.5:2. The calculated amount of salt was dissolved in double distilled water at room temperature. This solution was heated and kept for slow evaporation to dryness at room temperature. BTCZC salt was synthesized according to the reaction: ZnCl2 + CdCl2 + 2[NH2 CSNH2 ] → ZnCd[NH2 CSNH2 ]2 [Cl2 ]2 The purity of synthesized salt was further increased by successive recrystallization process. 2.2. Solubility The solubility of BTCZC was determined for four different temperatures, 30, 35, 40 and 45 ◦ C by dissolving the solute in deionized water in an airtight container maintained at a constant temperature with stirring. After saturation was attained, the equilibrium concentration of the solute was analyzed gravimetrically. The same procedure was repeated and the solubility curve for different temperature was drawn. 2.3. Crystal growth In the present study, BTCZC crystals were grown by using slow evaporation technique. Recrystallized salt of BTCZC was taken as raw material. Saturated BTCZC solution was prepared at room temperature with water as solvent. BTCZC is found to have a positive gradient of solubility. The prepared solution was filtered with a microfilter. The pH of this solution is 5.0. The solution was taken in vessels and closed with perforated covers and kept in a dust-free atmosphere. The crystals were harvested when they attained an optimal size and shape. 3. Characterization The single crystal X-ray diffraction pattern of BTCZC crystal was carried out using ENRAF NONIUS CAD4 X-ray diffractometer and its lattice parameters were determined. Fourier transform infrared spectrum was recorded by the KBr pellet technique using a BRUKER 66 V FTIR spectrometer to confirm the vibrational structure of the crystalline compound with the range of wavenumber 400–4000 cm−1 . UV–vis spectrum was recorded in the range of 200–2000 nm using VARIAN CARY 5E spectrometer. Thermal behavior of the grown sample was studied by using STA 1500 thermal analyzer. The NLO property of BTCZC was tested by Kurtz powder SHG test using an Nd:YAG laser. 4. Results and discussion
Fig. 1. FTIR spectrum of BTCZC crystal.
revealed that the grown crystal belongs to orthorhombic sys˚ tem with space group P21 21 21 unit cell parameters a = 11.918 A, ˚ b = 6.821 A˚ and c = 13.114 A. 4.2. FTIR studies The Fourier transform infrared (FTIR) spectrum of BTCZC is shown in Fig. 1. The assignment of various internal modes observed in these FTIR spectra is given in the Table 1. The assignments correspond to various internal vibrations of thiourea. Crystal structure investigations of thiourea have established the coplanarity structure of C, N and S atoms in the molecule [11]. In BTCZC complex, there are two possibilities by which the coordination of cadmium and zinc with thiourea can occur. It may occur either through nitrogen or sulfur of thiourea. The bands observed in the 3000–3500 cm−1 region in the FTIR spectra, at 3197, 3282 and 3389 cm−1 are characteristics of NH2 asymmetric and symmetric stretching vibrations and are in agreement with other compounds containing thiourea molecule CS(NH2 )2 [12–15]. The strong band observed at 1616 cm−1 in the BTCZC complex correspond to a band at 1625 cm−1 of thiourea, which is attributed to the NH2 deformation vibration similar to those of some metal thiourea complexes [16]. The band at 1477 cm−1 assigned to the N–C–N stretching vibration in thiourea is shifted to 1493 cm−1 in the BTCZC complex. This shift may be due to the greater double bond character of the carbon-to-nitrogen bond on complex formation. The appearance of band 1435 cm−1 and 1396 cm−1 for BTCZC against the absorption of pure thiourea at 1414 cm−1 confirms the formation of coordination. Lower shift of Table 1 Assignment of FTIR Frequencies (cm−1 ) Thiourea
BTCZC
Assignment
3380 3279 3177 1617 1477
3389 3282 3197 1616 1493
N–H stretching vibration N–H stretching vibration O–H stretching vibration N–H bending vibration N–C–N stretching vibration
1414
1435 1396
NH2 rocking vibration C S stretching vibration
1082 730 487 457
1096 713 474 530
NH2 rocking vibration C S stretching vibration N–C–N bending vibration S–C–N stretching vibration
4.1. Single crystal XRD To determine the unit cell parameters, the grown crystals were subjected to single crystal X-ray diffraction studies using Enraf Nonius CAD4 single crystal X-ray diffractometer. The X-ray analysis
K. Kirubavathi et al. / Spectrochimica Acta Part A 71 (2008) 1–4
Fig. 2. Optical spectrum of BTCZC crystal.
C S stretching frequency (730 – 713 cm−1 ) confirms the formation of metal–sulfur coordination bond [17]. These observations suggest that the metal coordinate with thiourea through sulfur in BTCZC. 4.3. UV–vis studies The UV–vis optical absorption and transmittance spectral analyses of BTCZC single crystal were carried out between 200 and 2000 nm. The transmittance spectrum (Fig. 2) depicts the transparency of the crystal is closed to 68% at 260 nm. But around 260 nm, there is a sharp decrease in transmittance due to absorbance leading to electronic excitation in this region. The cut-off frequency is 260 nm. At the longer wavelength side, the crystal is highly transparent (70%) upto 1800 nm. The absence of absorption in this region between 300 and 1800 nm shows that this crystal could be used for optical window applications. The absorption spectrum (Fig. 2) illustrates that there is a less absorbance in the entire UV–vis region. The lower cut-off wavelength of the crystal was found to be 260 nm. 4.4. Thermal studies A powdered sample weighing 1.871 mg was used for the analyses. The analyses were carried out simultaneously in nitrogen at a heating rate of 20 ◦ C/min for a temperature range of 30–600 ◦ C
3
and its represented in Fig. 3. Quite interesting and important to be notices is the very good thermal stability of the material upto 201 ◦ C. Another important observation is that, there is no phase transition till the material melts and this enhances the temperature range for the utility of the crystal for NLO applications. The absence of water of crystallization in the molecular structure is indicated by the absence of the weight loss around 100 ◦ C. The DTA curve shows as endothermic peak at 201 ◦ C which corresponds to the melting point of the compound. The peak of the endothermic represents the temperature at which the melting terminates which corresponds to its melting point at 209 ◦ C. Ideally, the melting portion of the trace corresponds to a vertical line. The TG curve of this sample indicates that the sample is stable up to 207 ◦ C after this temperature, this sample undergoes appreciable weight loss. The change in weight loss confirms the decomposing nature of the sample. The sharpness of the endothermic peak shows good degree of crystallinity of the grown ingot. The endothermic peak at 247 ◦ C indicates a phase change from liquid to vapor state as evidence from the loss of weight in TG curve. 4.5. Second harmonic generation The second harmonic generation (SHG) test on the BTCZC crystal was performed by Kurtz powder SHG method [18]. The powdered sample of BTCZC crystal was illuminated using the fundamental beam of 1064 nm from Q-switched Nd:YAG laser. Pulse energy 4 mJ/pulse and pulse width of 10 ns and repetition rate of 10 Hz were used. The second harmonic signal generated in the crystalline sample was confirmed from the emission of green radiation of wavelength 532 nm collected a monochromator after separating the 1064 nm pump beam with an IR-blocking filter. A photo multiplier tube as used as detector. It is observed that the measured SHG efficiency of BTCZC crystal was 1.1 times that of potassium dihydrogen phosphate (KDP). 5. Conclusion Bis (thiourea) cadmium zinc chloride (BTCZC) single crystals were grown by slow solvent evaporation technique for the first time. The crystallinity of the grown crystal was confirmed by single crystal X-ray diffraction analysis. Various functional groups present in the grown crystal was identified by FTIR spectrum. The optical quality of the grown crystal was justified by optical transmission studies. Thermal stability of the grown crystal was studied by TG & DTA analyses. The powder SHG measurement shows the grown BTCZC crystal having 1.1 times higher NLO efficiency than KDP. References
Fig. 3. TG/DTA curve of BTCZC crystal.
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