- Email: [email protected]
Effect of L -Cysteine doping on growth and some characteristics of potassium dihydrogen phosphate single crystals
Author’s Accepted Manuscript Effect of L-Cysteine Doping on Growth and Some Characteristics of Potassium Dihydrogen Phosphate Single Crystals Ashwini Mahadik, P.H. Soni, C.F. Desai www.elsevier.com/locate/physb
PII: DOI: Reference:
S0921-4526(17)30704-4 https://doi.org/10.1016/j.physb.2017.09.109 PHYSB310335
To appear in: Physica B: Physics of Condensed Matter Received date: 18 July 2017 Revised date: 25 September 2017 Accepted date: 26 September 2017 Cite this article as: Ashwini Mahadik, P.H. Soni and C.F. Desai, Effect of LCysteine Doping on Growth and Some Characteristics of Potassium Dihydrogen Phosphate Single Crystals, Physica B: Physics of Condensed Matter, https://doi.org/10.1016/j.physb.2017.09.109 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of L-Cysteine Doping on Growth and Some Characteristics of Potassium Dihydrogen Phosphate Single Crystals Ashwini Mahadik, P. H. Soni* and C. F. Desai Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara390002 *
Email id: [email protected]
Abstract: Among quite a number of technologically important NLO materials, Potassium Dihydrogen Phosphate (KDP) is one of the most favourable ones for second harmonic generation applications, such as in electro-optic modulators, parametric oscillators and harmonic generators. The authors report here their studies on KDP crystals doped with L-Cysteine (1mol% and 2mol%). The dopant inclusion in the crystals was confirmed using Fourier transform infrared (FT-IR) spectroscopy and Powder X-Ray Diffraction (XRD). The XRD results also confirm the tetragonal structure with lattice parameters a=b=7.45 Å and c=6.98Å. The presence of functional groups of crystals was analyzed using the FTIR spectra. For band gap evaluation, UV-Vis spectra were used and it was found to be 3.41 eV, 4.40eVand 4.50eV, respectively in the cases of pure KDP, 1mol% and 2mol% L-Cysteine dopings. The spectra quality indicates good transparency of the doped crystals in the visible region, a feature quite desirable for applications in optoelectronics. Keywords: A1 Doping and X-ray diffraction, A2 Growth from solutions and seed crystals, B3 Nonlinear optical Introduction: Crystal growth is a vital and an important field of experimental materials science and engineering, since they are required for fundamental data acquisition and for practical devices such as detectors, integrated circuits and for other applications. In the field of non-linear optical applications, the ferroactive crystals have now been established to be nearly indispensable. Particularly, KDP (KH2PO4), the crystal in the present investigation stands out in this respect. Growth and characterization of single crystals are inevitable for enhancing/modifying their properties [1, 2]. Amino acid doping in KDP (and the like) crystals is known to affect their properties from fair to large extent [3]. Herein, we
report doping with L-Cysteine and its effect on KDP. L-Cysteine differs from all other amino acids, particularly sulfur amino acids, in that it has a sulfhydryl group in its molecular structure making it very strongly reactive and serving as a strong reducing factor, while its chirality would expectedly enhance the charge asymmetry feature of the non-centro symmetric crystal. Single crystals of KDP are paraelectric at room temperature and have a large non-linear optical coefficient, good structural quality and mechanical properties. The para-electric phase has a tetragonal unit cell (space group I ̅ 2d) with parameters a=b=7.448Å and c=6.977Å and offers high transmittance across the visible spectral region and meets requirements for optical birefringence which is large enough to bracket the refractive index for even extreme wavelengths over which it is transparent [4]. The crystal can withstand repeated exposure to high power density laser without inducing strains and subsequent inhomogeneities in the refractive index [5]. These characteristics make it a desirable material as an efficient tuned dielectric medium for optical harmonic generation in and near the visible region and becomes useful for frequency doubling and mixing of many laser wavelengths between 1060nm and 525nm [6-9]. It is significant to note that its acousto-optic application is far superior to other existing deep UV materials. It has high transparency in the deep UV region. It also exhibits significant quadratic elecro-optic effect. Probably, its only drawback is its instability due to hygroscopic nature, posing stringent requirement on device packaging [10-11]. Amino acids have been attractive dopants for Potassium Dihydrogen Phosphate(KDP) since they themselves exhibit NLO property and also possess some specific features of interest such as (i) molecular chirality, which ensures non-centrosymmetric crystal structure, (ii) absence of strongly conjugated bonds, the feature that leads to wide transparency range in the visible and ultraviolet (UV) spectral regions and (iii) Zwitter ionic nature of the molecule that favors crystal hardness for applications in devices [12]. Complexes of amino acids with inorganic salts are considered to be novel materials for Second Harmonic Generation (SHG) and are found most of the time to be as promising as KDP or even better [13,14]. Among amino acid dopants, L-cysteine is quite different as mentioned above; however, there is no work report found in literature on L-Cysteine doping of KDP crystal. In the present study, we have used 1 mol% and 2 mol% L-Cysteine for the doping. Crystals were aqueous
solution grown and characterized using techniques such as Powder XRD, UV-Visible and FTIR Spectroscopies with an aim to inspect modifications in physico-chemical properties of the crystals. 2. Experimental: KDP and L-Cysteine used were both of AR grade. Room temperature aqueous saturated solution of KDP and L-Cysteine (1mol % and 2mol %) was used to obtain seed crystals over a period of 2-4 days. A suitable seed crystal was immersed in the supersaturated solution using a silk thread and left undisturbed in a beaker with a lid allowing controlled evaporation. The FTIR spectra were obtained using KBr pellet technique and analyzed in the wavenumber range of 400-4000 cm-1 using JASCO FTIR-4100 series spectrometer. For acquiring X-ray diffraction data, Bruker D8 Advance X-ray diffractometer was employed. The optical transmittance spectra were recorded in the wavelength region of 200 to 900 nm using Perkin Elmer Lambda 35 UV/Vis spectrometer. 3. Results and Discussion: 3.1 Crystal Growth: The pure KDP seed crystallite appearance took 3 days at the most, whereas, L-Cysteine doped KDP seed crystallites appeared only after 3-4 days. The growth rate of the doped crystals itself was also observed to be more than that of the pure crystals. After 28-30 days, fairly grown crystals were harvested. The average size of the pure KDP crystals obtained was 7.0 x 6.5 x 3.0 mm3 while that of the L-Cysteine doped KDP crystals, with 1 mol% and 2 mol% dopings, was 9.0 x 7.0 x 3.0 mm3 and 10.0 x 5.5 x 2.0 mm3, respectively. Figure 1 shows pure and doped crystals obtained. The overall appearance of the other crystals was similar. The doped as well as pure crystals were observed to have fair to good transparency. The doped crystals exhibited elongated shape along the c-axis as compared to pure KDP crystals.
3.2 Powder X-ray Diffraction analysis: Figures 2, 3 and 4 show the powder X-ray diffraction plots of pure KDP and 1mol% and 2mol% L-Cysteine doped KDP crystals, respectively. Sharp and definitive Bragg’s peaks, observed to correspond to the KDP structure and indexed accordingly, imply good crystalline perfection of the samples and any structural change due to doping being absent. The dopant does not show up its own phase as expected. 3.3 FTIR Spectral Analysis: Through the FTIR spectra, the presence of fundamental groups and their vibrational modes in the pure KDP and L-Cysteine doped KDP was confirmed (Fig. 5). Few bands of KDP become broader and some of the frequencies get slightly shifted due to KDP bonds overlapping the amino acid vibrations. The wavelengths and corresponding modes assigned are listed in Table -1 below. Table 1: Characteristic Absorption Frequencies of Various Functional Groups Wave number (cm)-1
Bonds
2926 2361 1630 1553 1363 1222 1197 1141 1108 997 962 659 586 533 408 362-448
OH asymmetric stretch P-O-H bending O=P-OH stretch NH3 bending CO2 symmetric stretch CH2 bending, P=O symmetric stretching CH2 Twist P- O-H symmetric stretching NH3 rock N–CH stretch SH bending CH–CO2stretch P-OH deformation/K-O stretching CH2–CH–N bend PO4 stretching CCN bending
3.4 Optical Transmittance: The optical transmittance spectra obtained are shown in figure 6. For optical device fabrication, the crystal should be highly transparent in a considerable range of wavelength [15, 16]. The good overall high transmittance of the crystals in the entire visible region suggests its suitability for
second harmonic generation and NLO devices [17, 18]. The dependence of optical absorption coefficient on the photon energy can be used to evaluate the band gap [19]. The plots of (αE)2 versus E, Tauc plots, where E = the photon energy and α = absorption coefficient, for pure KDP and 1mol% and 2mol% L-Cysteine doped KDP crystals are shown in figure 7. The band gap Eg was evaluated using extrapolation of the linear part on the high energy side of the spectrum. The doping of L-Cysteine in KDP raises its band gap from 3.41 eV to 4.40 eV and 4.50 eV, respectively, at 1 mol% and 2 mol% of doping levels. This is quite a significant increase in the KDP band gap. Optical band gap enhancement due to amino acid doping is well known, for example in the case of ADP (Ammonium Dihydrogen Phosphate), implying possibility of increased SHG efficiency [20]. As a consequence of the wide band gap, the crystals have large transmittance in the visible edge to IR regions, attesting the suitability of the crystals for photonic and optical applications [21]. It was also observed that the cut-off wavelengths of the Cy1mol% and Cy2mol% doped KDP crystals are about 252 nm and 240 nm, respectively; however, the cut-off wavelength of pure KDP was observed at 256 nm. With these observations, the L-Cysteine doping of KDP crystals may prove more useful. In addition, it can be noted that the entire region does not show any absorption band offering excellent transparency in the visible region of the spectrum.
Conclusions: L-Cysteine (1mol% and 2mol%) doped crystals of KDP can be successfully be grown with quite good perfection using slow evaporation method at room temperature. The doping apparently seems to imply increased crystal growth rate. The doped crystals have very good transmittance, on average 77%, in the entire UV-Visible and IR region. Interestingly, L-Cysteine doping in KDP crystals increases the band gap, from 3.41 eV to 4.40 eV and to 4.50eV, respectively, with doping levels of 1mol% and 2mol%, making it more suitable for SHG application.
Acknowledgement:
The authors are grateful to UGC, New Delhi, for providing financial assistance through SAP Program and to Department of Metallurgical and Materials Engineering and Department of Chemistry, The Maharaja Sayajirao University of Baroda, for providing some of their laboratory facilities.
References: 1. R. A. Laudise, R. Ueda and J.B. Mullin (1975) (Eds.), Crystal Growth and Characterization, North-Holland Publishing Company, Amsterdam pp. 255-277. 2. H. S. Nalwa, S. Miyata, Eds., Nonlinear Optics of Organic Molecules and Polymers, CRC Press, New York (1997). 3. S. B. Monaco, L. E. Davis, S. P. Velsko, F. T. Wang, D. Eimerl, Synthesis and characterization of chemical analogs of L-arginine phosphate, J. Cryst. Growth, 85 (1987) pp. 252-255. 4.
J. Podder, The Study of Impurities Effect on the Growth and Nucleation Kinetics of Potassium Dihydrogen Phosphate, J. Cryst. Growth, 237-239 Part 1 (2002) pp. 70-75.
5.
H. Endert and W. Melle, Laser-Induced Damage in KDP Crystals. The Influence of Growth Ghosts and Growth Bands, Phys. Stat. Solidi, 74 (1982) pp. 141-148.
6. H. V. Alexandru, S. Antohe, Prismatic faces of KDP crystal, kinetic and mechanism of growth from solutions, J. Cryst. Growth, 258 (2003) pp. 149-157. 7.
H. V. Alexandru, KDP prismatic faces: kinetics and the mechanism of their growth from solutions, J. Cryst. Growth, 166 (1996) pp.162-166.
8.
V. I. Bredikhin, G. L. Galushkina, A. A. Kulagin, S. P. Kuznetsov, O. A. Malshakova, Competing growth centers and step bunching in KDP crystal growth from solutions, J. Cryst. Growth, 259 (2003) pp. 309-320.
9.
N. A. Booth, A. A. Chernov, P. G. Vekilov, Characteristic length scales of step bunching in KDP crystal growth: in situ differential phase-shifting interferometry study, J. Cryst. Growth, 237-239 Part 3 (2002) pp. 1818-1824.
10. Neelam Gupta and Vitaly Voloshinov, Spectral characterization in deep UV of an improved imaging KDP acousto-optic tunable filter, Jr. of Optics, IOP, 16 (2014). 11. Mark J. Gunning, Roger E. Raab, Wlodimierz Kucharczyk, Magnitude and nature of the quadractic electro-optic effect in potassium dihydrogen phosphate and ammonium dihydrogen phosphate crytsals, J. Opt. Soc. Am., Part B, 18(8) (2001) pp. 1092-1098. 12. Nicoud, R. J. Twieg, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, New York (1987). 13. S.B. Monaco, L. E. Davis, S. P. Velsko, F. T. Wang, D. Eimerl, Synthesis and characterization of chemical analogs of L-arginine phosphate, J. Cryst. Growth, 85 (1987) pp. 252-255. 14. M. N. Bhat, S. M. Dharmaprakash, New nonlinear optical material: glycine sodium nitrate, J. Cryst. Growth, 235 (2002) pp. 511-516. 15. V. Krishnakumar and R. Nagalakshmi, Crystal Growth and Vibrational Spectroscopic Studies of the Semiorganic Non-linear Optical Crystal-Bisthiourea Zinc Chloride,Spectrochimica Acta Part A, Spectrochimica Acta Part A, 61(3) (2005) pp. 499-507. 16. V. Krishnakumar and R. J. Xavier, FT Raman and FTIR Spectral Studies of 3-Mercapto-1,2,4Triazole,SpectrochimicaActa Part A, 60(3) (2004) pp. 709- 714. 17. S. AnieRoshan, C. Joseph, M. A. Ittyachen, Growth and characterization of a new metal-organic crystal: potassium thiourea bromide, Mater. Lett., 49 (2001) pp. 299-302. 18. V. Venkataramanan, S. Maheswaran, J. N. Sherwood, H. L. Bhat, Crystal growth and physical characterization of the semiorganic bis(thiourea) cadmium chloride, J. Cryst. Growth, 179 (1997) pp. 605-610. 19. N. Tigau, V. Ciupinaa, G. Prodana, G. I. Rusub, C. Gheorghies and E. Vasilec, Influence of Thermal Annealing in Air on the Structural and Optical Properties of Amorphous Antimony Trisulfide Thin Films, J. of Optoelectronics and Adv. Mater., 6(1) (2004) pp. 211-217. 20. R. N. Shaikh, M.D. Shirsat, P.M. Koinkar, S.S. Hussaini, Effect of L-cysteine on optical, thermal and mechanical properties of ADP crystal for NLO application, Opt. and Laser Tech., 69 (2015) pp. 8-12.
21.
S. Suresh, A. Ramanand, D. Jayaraman and S.M. Navis Priya, Growth Kinetics and Optical and Mechanical Properties of Glycine Lithium Sulphate (GLS) Crystals, J. of Minerals & Mater. Charactr. & Engg., 9(12) (2010) pp. 1071-1080.
List of figures: Fig. 1: As grown crystals of pure and doped KDP Fig. 2: XRD of Pure KDP Fig. 3: XRD of KDP + L-Cy 1mole% Fig. 4: XRD of KDP + L-Cy 2mole% Fig. 5: FTIR of Pure KDP and L-Cy 1mole% and L-Cy 2mole% doped KDP Fig. 6: UV-Vis Spectra of pure and doped KDP crystals Fig. 7: Tauc plots and Band gaps of Pure and Doped KDP
PII: DOI: Reference:
S0921-4526(17)30704-4 https://doi.org/10.1016/j.physb.2017.09.109 PHYSB310335
To appear in: Physica B: Physics of Condensed Matter Received date: 18 July 2017 Revised date: 25 September 2017 Accepted date: 26 September 2017 Cite this article as: Ashwini Mahadik, P.H. Soni and C.F. Desai, Effect of LCysteine Doping on Growth and Some Characteristics of Potassium Dihydrogen Phosphate Single Crystals, Physica B: Physics of Condensed Matter, https://doi.org/10.1016/j.physb.2017.09.109 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of L-Cysteine Doping on Growth and Some Characteristics of Potassium Dihydrogen Phosphate Single Crystals Ashwini Mahadik, P. H. Soni* and C. F. Desai Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara390002 *
Email id: [email protected]
Abstract: Among quite a number of technologically important NLO materials, Potassium Dihydrogen Phosphate (KDP) is one of the most favourable ones for second harmonic generation applications, such as in electro-optic modulators, parametric oscillators and harmonic generators. The authors report here their studies on KDP crystals doped with L-Cysteine (1mol% and 2mol%). The dopant inclusion in the crystals was confirmed using Fourier transform infrared (FT-IR) spectroscopy and Powder X-Ray Diffraction (XRD). The XRD results also confirm the tetragonal structure with lattice parameters a=b=7.45 Å and c=6.98Å. The presence of functional groups of crystals was analyzed using the FTIR spectra. For band gap evaluation, UV-Vis spectra were used and it was found to be 3.41 eV, 4.40eVand 4.50eV, respectively in the cases of pure KDP, 1mol% and 2mol% L-Cysteine dopings. The spectra quality indicates good transparency of the doped crystals in the visible region, a feature quite desirable for applications in optoelectronics. Keywords: A1 Doping and X-ray diffraction, A2 Growth from solutions and seed crystals, B3 Nonlinear optical Introduction: Crystal growth is a vital and an important field of experimental materials science and engineering, since they are required for fundamental data acquisition and for practical devices such as detectors, integrated circuits and for other applications. In the field of non-linear optical applications, the ferroactive crystals have now been established to be nearly indispensable. Particularly, KDP (KH2PO4), the crystal in the present investigation stands out in this respect. Growth and characterization of single crystals are inevitable for enhancing/modifying their properties [1, 2]. Amino acid doping in KDP (and the like) crystals is known to affect their properties from fair to large extent [3]. Herein, we
report doping with L-Cysteine and its effect on KDP. L-Cysteine differs from all other amino acids, particularly sulfur amino acids, in that it has a sulfhydryl group in its molecular structure making it very strongly reactive and serving as a strong reducing factor, while its chirality would expectedly enhance the charge asymmetry feature of the non-centro symmetric crystal. Single crystals of KDP are paraelectric at room temperature and have a large non-linear optical coefficient, good structural quality and mechanical properties. The para-electric phase has a tetragonal unit cell (space group I ̅ 2d) with parameters a=b=7.448Å and c=6.977Å and offers high transmittance across the visible spectral region and meets requirements for optical birefringence which is large enough to bracket the refractive index for even extreme wavelengths over which it is transparent [4]. The crystal can withstand repeated exposure to high power density laser without inducing strains and subsequent inhomogeneities in the refractive index [5]. These characteristics make it a desirable material as an efficient tuned dielectric medium for optical harmonic generation in and near the visible region and becomes useful for frequency doubling and mixing of many laser wavelengths between 1060nm and 525nm [6-9]. It is significant to note that its acousto-optic application is far superior to other existing deep UV materials. It has high transparency in the deep UV region. It also exhibits significant quadratic elecro-optic effect. Probably, its only drawback is its instability due to hygroscopic nature, posing stringent requirement on device packaging [10-11]. Amino acids have been attractive dopants for Potassium Dihydrogen Phosphate(KDP) since they themselves exhibit NLO property and also possess some specific features of interest such as (i) molecular chirality, which ensures non-centrosymmetric crystal structure, (ii) absence of strongly conjugated bonds, the feature that leads to wide transparency range in the visible and ultraviolet (UV) spectral regions and (iii) Zwitter ionic nature of the molecule that favors crystal hardness for applications in devices [12]. Complexes of amino acids with inorganic salts are considered to be novel materials for Second Harmonic Generation (SHG) and are found most of the time to be as promising as KDP or even better [13,14]. Among amino acid dopants, L-cysteine is quite different as mentioned above; however, there is no work report found in literature on L-Cysteine doping of KDP crystal. In the present study, we have used 1 mol% and 2 mol% L-Cysteine for the doping. Crystals were aqueous
solution grown and characterized using techniques such as Powder XRD, UV-Visible and FTIR Spectroscopies with an aim to inspect modifications in physico-chemical properties of the crystals. 2. Experimental: KDP and L-Cysteine used were both of AR grade. Room temperature aqueous saturated solution of KDP and L-Cysteine (1mol % and 2mol %) was used to obtain seed crystals over a period of 2-4 days. A suitable seed crystal was immersed in the supersaturated solution using a silk thread and left undisturbed in a beaker with a lid allowing controlled evaporation. The FTIR spectra were obtained using KBr pellet technique and analyzed in the wavenumber range of 400-4000 cm-1 using JASCO FTIR-4100 series spectrometer. For acquiring X-ray diffraction data, Bruker D8 Advance X-ray diffractometer was employed. The optical transmittance spectra were recorded in the wavelength region of 200 to 900 nm using Perkin Elmer Lambda 35 UV/Vis spectrometer. 3. Results and Discussion: 3.1 Crystal Growth: The pure KDP seed crystallite appearance took 3 days at the most, whereas, L-Cysteine doped KDP seed crystallites appeared only after 3-4 days. The growth rate of the doped crystals itself was also observed to be more than that of the pure crystals. After 28-30 days, fairly grown crystals were harvested. The average size of the pure KDP crystals obtained was 7.0 x 6.5 x 3.0 mm3 while that of the L-Cysteine doped KDP crystals, with 1 mol% and 2 mol% dopings, was 9.0 x 7.0 x 3.0 mm3 and 10.0 x 5.5 x 2.0 mm3, respectively. Figure 1 shows pure and doped crystals obtained. The overall appearance of the other crystals was similar. The doped as well as pure crystals were observed to have fair to good transparency. The doped crystals exhibited elongated shape along the c-axis as compared to pure KDP crystals.
3.2 Powder X-ray Diffraction analysis: Figures 2, 3 and 4 show the powder X-ray diffraction plots of pure KDP and 1mol% and 2mol% L-Cysteine doped KDP crystals, respectively. Sharp and definitive Bragg’s peaks, observed to correspond to the KDP structure and indexed accordingly, imply good crystalline perfection of the samples and any structural change due to doping being absent. The dopant does not show up its own phase as expected. 3.3 FTIR Spectral Analysis: Through the FTIR spectra, the presence of fundamental groups and their vibrational modes in the pure KDP and L-Cysteine doped KDP was confirmed (Fig. 5). Few bands of KDP become broader and some of the frequencies get slightly shifted due to KDP bonds overlapping the amino acid vibrations. The wavelengths and corresponding modes assigned are listed in Table -1 below. Table 1: Characteristic Absorption Frequencies of Various Functional Groups Wave number (cm)-1
Bonds
2926 2361 1630 1553 1363 1222 1197 1141 1108 997 962 659 586 533 408 362-448
OH asymmetric stretch P-O-H bending O=P-OH stretch NH3 bending CO2 symmetric stretch CH2 bending, P=O symmetric stretching CH2 Twist P- O-H symmetric stretching NH3 rock N–CH stretch SH bending CH–CO2stretch P-OH deformation/K-O stretching CH2–CH–N bend PO4 stretching CCN bending
3.4 Optical Transmittance: The optical transmittance spectra obtained are shown in figure 6. For optical device fabrication, the crystal should be highly transparent in a considerable range of wavelength [15, 16]. The good overall high transmittance of the crystals in the entire visible region suggests its suitability for
second harmonic generation and NLO devices [17, 18]. The dependence of optical absorption coefficient on the photon energy can be used to evaluate the band gap [19]. The plots of (αE)2 versus E, Tauc plots, where E = the photon energy and α = absorption coefficient, for pure KDP and 1mol% and 2mol% L-Cysteine doped KDP crystals are shown in figure 7. The band gap Eg was evaluated using extrapolation of the linear part on the high energy side of the spectrum. The doping of L-Cysteine in KDP raises its band gap from 3.41 eV to 4.40 eV and 4.50 eV, respectively, at 1 mol% and 2 mol% of doping levels. This is quite a significant increase in the KDP band gap. Optical band gap enhancement due to amino acid doping is well known, for example in the case of ADP (Ammonium Dihydrogen Phosphate), implying possibility of increased SHG efficiency [20]. As a consequence of the wide band gap, the crystals have large transmittance in the visible edge to IR regions, attesting the suitability of the crystals for photonic and optical applications [21]. It was also observed that the cut-off wavelengths of the Cy1mol% and Cy2mol% doped KDP crystals are about 252 nm and 240 nm, respectively; however, the cut-off wavelength of pure KDP was observed at 256 nm. With these observations, the L-Cysteine doping of KDP crystals may prove more useful. In addition, it can be noted that the entire region does not show any absorption band offering excellent transparency in the visible region of the spectrum.
Conclusions: L-Cysteine (1mol% and 2mol%) doped crystals of KDP can be successfully be grown with quite good perfection using slow evaporation method at room temperature. The doping apparently seems to imply increased crystal growth rate. The doped crystals have very good transmittance, on average 77%, in the entire UV-Visible and IR region. Interestingly, L-Cysteine doping in KDP crystals increases the band gap, from 3.41 eV to 4.40 eV and to 4.50eV, respectively, with doping levels of 1mol% and 2mol%, making it more suitable for SHG application.
Acknowledgement:
The authors are grateful to UGC, New Delhi, for providing financial assistance through SAP Program and to Department of Metallurgical and Materials Engineering and Department of Chemistry, The Maharaja Sayajirao University of Baroda, for providing some of their laboratory facilities.
References: 1. R. A. Laudise, R. Ueda and J.B. Mullin (1975) (Eds.), Crystal Growth and Characterization, North-Holland Publishing Company, Amsterdam pp. 255-277. 2. H. S. Nalwa, S. Miyata, Eds., Nonlinear Optics of Organic Molecules and Polymers, CRC Press, New York (1997). 3. S. B. Monaco, L. E. Davis, S. P. Velsko, F. T. Wang, D. Eimerl, Synthesis and characterization of chemical analogs of L-arginine phosphate, J. Cryst. Growth, 85 (1987) pp. 252-255. 4.
J. Podder, The Study of Impurities Effect on the Growth and Nucleation Kinetics of Potassium Dihydrogen Phosphate, J. Cryst. Growth, 237-239 Part 1 (2002) pp. 70-75.
5.
H. Endert and W. Melle, Laser-Induced Damage in KDP Crystals. The Influence of Growth Ghosts and Growth Bands, Phys. Stat. Solidi, 74 (1982) pp. 141-148.
6. H. V. Alexandru, S. Antohe, Prismatic faces of KDP crystal, kinetic and mechanism of growth from solutions, J. Cryst. Growth, 258 (2003) pp. 149-157. 7.
H. V. Alexandru, KDP prismatic faces: kinetics and the mechanism of their growth from solutions, J. Cryst. Growth, 166 (1996) pp.162-166.
8.
V. I. Bredikhin, G. L. Galushkina, A. A. Kulagin, S. P. Kuznetsov, O. A. Malshakova, Competing growth centers and step bunching in KDP crystal growth from solutions, J. Cryst. Growth, 259 (2003) pp. 309-320.
9.
N. A. Booth, A. A. Chernov, P. G. Vekilov, Characteristic length scales of step bunching in KDP crystal growth: in situ differential phase-shifting interferometry study, J. Cryst. Growth, 237-239 Part 3 (2002) pp. 1818-1824.
10. Neelam Gupta and Vitaly Voloshinov, Spectral characterization in deep UV of an improved imaging KDP acousto-optic tunable filter, Jr. of Optics, IOP, 16 (2014). 11. Mark J. Gunning, Roger E. Raab, Wlodimierz Kucharczyk, Magnitude and nature of the quadractic electro-optic effect in potassium dihydrogen phosphate and ammonium dihydrogen phosphate crytsals, J. Opt. Soc. Am., Part B, 18(8) (2001) pp. 1092-1098. 12. Nicoud, R. J. Twieg, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, New York (1987). 13. S.B. Monaco, L. E. Davis, S. P. Velsko, F. T. Wang, D. Eimerl, Synthesis and characterization of chemical analogs of L-arginine phosphate, J. Cryst. Growth, 85 (1987) pp. 252-255. 14. M. N. Bhat, S. M. Dharmaprakash, New nonlinear optical material: glycine sodium nitrate, J. Cryst. Growth, 235 (2002) pp. 511-516. 15. V. Krishnakumar and R. Nagalakshmi, Crystal Growth and Vibrational Spectroscopic Studies of the Semiorganic Non-linear Optical Crystal-Bisthiourea Zinc Chloride,Spectrochimica Acta Part A, Spectrochimica Acta Part A, 61(3) (2005) pp. 499-507. 16. V. Krishnakumar and R. J. Xavier, FT Raman and FTIR Spectral Studies of 3-Mercapto-1,2,4Triazole,SpectrochimicaActa Part A, 60(3) (2004) pp. 709- 714. 17. S. AnieRoshan, C. Joseph, M. A. Ittyachen, Growth and characterization of a new metal-organic crystal: potassium thiourea bromide, Mater. Lett., 49 (2001) pp. 299-302. 18. V. Venkataramanan, S. Maheswaran, J. N. Sherwood, H. L. Bhat, Crystal growth and physical characterization of the semiorganic bis(thiourea) cadmium chloride, J. Cryst. Growth, 179 (1997) pp. 605-610. 19. N. Tigau, V. Ciupinaa, G. Prodana, G. I. Rusub, C. Gheorghies and E. Vasilec, Influence of Thermal Annealing in Air on the Structural and Optical Properties of Amorphous Antimony Trisulfide Thin Films, J. of Optoelectronics and Adv. Mater., 6(1) (2004) pp. 211-217. 20. R. N. Shaikh, M.D. Shirsat, P.M. Koinkar, S.S. Hussaini, Effect of L-cysteine on optical, thermal and mechanical properties of ADP crystal for NLO application, Opt. and Laser Tech., 69 (2015) pp. 8-12.
21.
S. Suresh, A. Ramanand, D. Jayaraman and S.M. Navis Priya, Growth Kinetics and Optical and Mechanical Properties of Glycine Lithium Sulphate (GLS) Crystals, J. of Minerals & Mater. Charactr. & Engg., 9(12) (2010) pp. 1071-1080.
List of figures: Fig. 1: As grown crystals of pure and doped KDP Fig. 2: XRD of Pure KDP Fig. 3: XRD of KDP + L-Cy 1mole% Fig. 4: XRD of KDP + L-Cy 2mole% Fig. 5: FTIR of Pure KDP and L-Cy 1mole% and L-Cy 2mole% doped KDP Fig. 6: UV-Vis Spectra of pure and doped KDP crystals Fig. 7: Tauc plots and Band gaps of Pure and Doped KDP