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Growth of non-linear optical γ-glycine single crystals and their characterization
Optical Materials 30 (2007) 40–43 www.elsevier.com/locate/optmat
Growth of non-linear optical c-glycine single crystals and their characterization K. Srinivasan *, J. Arumugam Crystal Research Centre, Alagappa University, Karaikudi 630 003, Tamil Nadu, India Available online 9 January 2007
Abstract The non-linear optical c-glycine single crystals were grown by low temperature solution growth methods from aqueous solutions with incorporation of known amount of sodium chloride as additive. Crystals were grown from pure aqueous solutions of glycine with a range of sodium chloride concentration. The change in morphology of the a-form of glycine with sodium chloride concentration and the occurrence of c form at a critical concentration of sodium chloride were studied. The form of crystallization was confirmed by X-ray power diffraction method and the optical transparency of the c-glycine in the UV–Vis–near IR region was studied by recording the optical transmittance spectrum. Ó 2006 Elsevier B.V. All rights reserved. PACS: 42.70.Mp; 81.10.Dn Keywords: Non-linear optical crystals; Growth from solutions; c-Glycine; Polymorphic phase transitions; X-ray diffraction; Thermal properties; Optical transmittance
1. Introduction Crystal growth of organic non-linear optical materials has significantly attracted in recent years because of their high value of non-linear optical coefficients. Glycine, a well-known amino acid, crystallizes in three different polymorphs: a, b, and c [1–3]. While a and b forms crystallize in centrosymmetric class, the c-glycine crystallizes in non-centrosymmetric space group P32 making it a potential candidate for non-linear optical applications especially for effective optical second harmonic generation [3,4]. It is reported that its second harmonic energy conversion efficiency is about 1.5 times that of KDP [5]. a and b forms crystallize from pure aqueous solutions but c form results from aqueous solutions with selected acetic or alkaline incorporations. b form is a most unstable. In the present work, single crystals of c-glycine were grown from aqueous solutions with incorporation of a range of sodium chloride *
Corresponding author. Tel.: +91 4565 225205; fax: +91 4565 225202. E-mail address: [email protected] (K. Srinivasan).
0925-3467/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2006.11.049
(NaCl) concentration by low temperature solution growth methods. The influence of NaCl addition on the form of crystallization and morphologies of the crystals were studied. X-ray powder diffraction was used to confirm the form of crystallization and the optical transparency was studied by UV–Vis–near IR spectroscopy.
2. Experimental The commercially available analytical grade glycine (amino acetic acid: NH2CH2COOH), sodium chloride and double distilled (DD) water were used for the crystal growth experiments. NaCl salt of different weights in the range from 1 to 12 g in 100 ml of double distilled water were dissolved in separate but similar vessels and glycine salt of known weight were added in each of the vessels, stirred well for about 6 h and saturated solutions were prepared at room temperature. Also, a pure aqueous solution was prepared in a similar vessel for comparison. The variation of solubility of glycine with NaCl concentration
Concentration of Glycine (g/100ml)
K. Srinivasan, J. Arumugam / Optical Materials 30 (2007) 40–43
41
32 31 30 29 28 27 26 0
2
4
6
8
10
12
14
Concentration of NaCl (g/100ml)
Fig. 1. Variation of glycine solubility in DD water with NaCl concentration.
was determined by gravimetric method and is indicated in Fig. 1. The solutions were filtered with Borosil No. 1 filter sheets and kept in a dust free atmosphere for evaporation. Nucleation was observed in the interval of 2–10 days from solutions with different concentrations of NaCl; while higher mixing concentrations of NaCl yield quick nucleation and higher rate, smaller concentrations yield slower nucleation with lower rate. The nucleated solutions were allowed for further growth and then harvested. Morphology of the resulted crystals from NaCl incorporated solutions was compared with the one resulted from pure solution. X-ray powder diffraction (XRD) spectrum of the crystals were recorded on an automated analytical MPD model diffractometer using Cu Ka radiation of wave˚ by step scanning between 10° and 70° length k = 1.5406 A in 2h. Optical transmittance spectrum was recorded for the grown crystals in the region 200–3000 nm by 500 Scan UV– Vis–NIR spectrometer. 3. Results and discussion 3.1. Growth of a-form and the effect of NaCl concentration on morphology Morphology of the grown crystals depends very much on the concentration of NaCl in the solution. Photograph of some of the crystals grown from pure aqueous solution is shown in Fig. 2. These have the usual morphology of aglycine with comparatively long growth along the ‘c’ direction than ‘a’. NaCl incorporation changes the actual morphology to the extent that it enhances the growth along the ‘a’ direction and reduces the growth along ‘c’. Because of this, the end morphology of the crystals appears more elongated along ‘a’ direction than that of ‘c’. This morphological change is more when the NaCl concentration increases. Photograph of some of the crystals grown from solution with 5 g NaCl concentration is shown in Fig. 3 for comparison.
Fig. 2. a-Glycine single crystals grown from pure aqueous solution.
Fig. 3. a-Glycine single crystals resulted from solution with 5 g of NaCl concentration in 100 ml of water.
The variation of crystal length along ‘a’ and ‘c’ directions of the grown crystals with NaCl concentration is shown in Fig. 4. This situation continuous until the NaCl concentration has reached a critical level (about 8 g in 100 ml of DD water) in the solution and the crystals resulted out of these solutions are a-form. This is confirmed by XRD. 3.2. Growth of c-form and optimum level of NaCl concentration Above the critical concentration of NaCl (>8 g) the solution yield crystals with different morphology and also belong to c-form. Photograph of some of the crystals resulted from aqueous solution with 8 g NaCl concentration is shown in Fig. 5. The resulted crystals have trigonal end with smooth facets at one end and truncated rough facets on the opposite end, which clearly indicates that the
42
K. Srinivasan, J. Arumugam / Optical Materials 30 (2007) 40–43 15
(110)
13
4000 Counts
Crystal Length (mm)
(210) 11 9
along 'a' along 'c'
7
(200)
2000
(211)
(100)
(400)
(101) 5
(300)
(201)
0 20
30
40
50
60
Position [°2 Theta]
3
Fig. 6. X-ray powder diffraction spectrum of c-glycine.
1 0
1
2
3
4
5
6
7
8
Fig. 4. Variation of crystal length along ‘a’ and ‘c’ directions with NaCl concentration.
Transmittance (%)
Concentration of NaCl (g/100ml of DD Water) 100 90 80 70 60 50 40 30 20 10 0 0
1000
500
1500
2000
2500
Wavalength (nm)
Fig. 7. Optical transmittance spectrum in the UV–Vis–near IR region of the grown c-glycine crystals.
constants of the crystal were determined. The grown c-glycine crystals belong to hexagonal system with space group ˚ and P32 and having lattice parameters a = b = 7.0371 A 3 ˚ ˚ c = 5.4665 A with cell volume 234.44 A . The determined lattice parameter values are in-line with the literature values [4,6]. Fig. 5. c-Glycine single crystals resulted from solution with 8 g of NaCl concentration in 100 ml of water.
crystal has stopped growing at one end and shows only unidirectional growth along its ‘c’ direction. This is a common feature which appears in many highly polar non-linear optical crystals and this behaviour had been reported recently [7]. When the NaCl concentration reached 12 g, the solution yield only crystals with completely destructed morphologies and therefore the optimum level of NaCl concentration to be added to get c-form is about 8–12 g in 100 ml of DD water. 3.3. X-ray powder diffraction study The c-form of these crystals was confirmed by XRD and the spectrum is given in Fig. 6. The recorded powder XRD pattern of a and b forms have showed marked differences as reported in the literature [5,6]. The reflection peaks corresponding to different crystal planes in the XRD spectrum were indexed and from the values of 2h, d-spacing, h k l and relative intensity (I/Io) of every prominent peak, the lattice
3.4. Optical transmittance The recorded optical transmittance spectrum given in Fig. 7 indicates that the grown c-glycine crystals having optical transparency window between 250 and 2600 nm and the lower cut-off wavelength is well below 300 nm in the UV region is the most desirable one for second harmonic generation in this region. 4. Conclusions c-Glycine single crystals were grown from aqueous solutions with NaCl as additives. The incorporation of NaCl in the solution has changed the morphology of the a-glycine significantly. At a critical concentration of NaCl, the solution yield c-glycine crystals. These crystals have unidirectional growth along one of the ‘c’ directions while the growth stops completely along the other ‘c’ direction. The optimum level of NaCl concentration to get c-form is about 8–12 g/100 ml of DD water at room temperature. The form of crystallization was confirmed by X-ray powder diffraction. The grown c-glycine crystals have optical
K. Srinivasan, J. Arumugam / Optical Materials 30 (2007) 40–43
transmittance window in the UV–Vis–near IR region between 250 and 2600 nm. References [1] G. Albrecht, R.B. Corey, J. Am. Chem. Soc. 61 (1939) 1087. [2] Y. Iitaka, Acta Crystallogr. 13 (1960) 35.
[3] [4] [5] [6]
43
Y. Iitaka, Acta Crystallogr. 11 (1958) 225. Y. Iitaka, Acta Crystallogr. 14 (1961) 1. M.N. Bhat, S.M. Dharmaprakash, J. Cryst. Growth 242 (2002) 245. G.L. Perlovich, L.K. Hansen, A. Bauer-Brandl, J. Therm. Anal. Calorim. 66 (2001) 699. [7] K. Srinivasan, J.N. Sherwood, Cryst. Growth Des. 5 (2005) 1359.
Growth of non-linear optical c-glycine single crystals and their characterization K. Srinivasan *, J. Arumugam Crystal Research Centre, Alagappa University, Karaikudi 630 003, Tamil Nadu, India Available online 9 January 2007
Abstract The non-linear optical c-glycine single crystals were grown by low temperature solution growth methods from aqueous solutions with incorporation of known amount of sodium chloride as additive. Crystals were grown from pure aqueous solutions of glycine with a range of sodium chloride concentration. The change in morphology of the a-form of glycine with sodium chloride concentration and the occurrence of c form at a critical concentration of sodium chloride were studied. The form of crystallization was confirmed by X-ray power diffraction method and the optical transparency of the c-glycine in the UV–Vis–near IR region was studied by recording the optical transmittance spectrum. Ó 2006 Elsevier B.V. All rights reserved. PACS: 42.70.Mp; 81.10.Dn Keywords: Non-linear optical crystals; Growth from solutions; c-Glycine; Polymorphic phase transitions; X-ray diffraction; Thermal properties; Optical transmittance
1. Introduction Crystal growth of organic non-linear optical materials has significantly attracted in recent years because of their high value of non-linear optical coefficients. Glycine, a well-known amino acid, crystallizes in three different polymorphs: a, b, and c [1–3]. While a and b forms crystallize in centrosymmetric class, the c-glycine crystallizes in non-centrosymmetric space group P32 making it a potential candidate for non-linear optical applications especially for effective optical second harmonic generation [3,4]. It is reported that its second harmonic energy conversion efficiency is about 1.5 times that of KDP [5]. a and b forms crystallize from pure aqueous solutions but c form results from aqueous solutions with selected acetic or alkaline incorporations. b form is a most unstable. In the present work, single crystals of c-glycine were grown from aqueous solutions with incorporation of a range of sodium chloride *
Corresponding author. Tel.: +91 4565 225205; fax: +91 4565 225202. E-mail address: [email protected] (K. Srinivasan).
0925-3467/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2006.11.049
(NaCl) concentration by low temperature solution growth methods. The influence of NaCl addition on the form of crystallization and morphologies of the crystals were studied. X-ray powder diffraction was used to confirm the form of crystallization and the optical transparency was studied by UV–Vis–near IR spectroscopy.
2. Experimental The commercially available analytical grade glycine (amino acetic acid: NH2CH2COOH), sodium chloride and double distilled (DD) water were used for the crystal growth experiments. NaCl salt of different weights in the range from 1 to 12 g in 100 ml of double distilled water were dissolved in separate but similar vessels and glycine salt of known weight were added in each of the vessels, stirred well for about 6 h and saturated solutions were prepared at room temperature. Also, a pure aqueous solution was prepared in a similar vessel for comparison. The variation of solubility of glycine with NaCl concentration
Concentration of Glycine (g/100ml)
K. Srinivasan, J. Arumugam / Optical Materials 30 (2007) 40–43
41
32 31 30 29 28 27 26 0
2
4
6
8
10
12
14
Concentration of NaCl (g/100ml)
Fig. 1. Variation of glycine solubility in DD water with NaCl concentration.
was determined by gravimetric method and is indicated in Fig. 1. The solutions were filtered with Borosil No. 1 filter sheets and kept in a dust free atmosphere for evaporation. Nucleation was observed in the interval of 2–10 days from solutions with different concentrations of NaCl; while higher mixing concentrations of NaCl yield quick nucleation and higher rate, smaller concentrations yield slower nucleation with lower rate. The nucleated solutions were allowed for further growth and then harvested. Morphology of the resulted crystals from NaCl incorporated solutions was compared with the one resulted from pure solution. X-ray powder diffraction (XRD) spectrum of the crystals were recorded on an automated analytical MPD model diffractometer using Cu Ka radiation of wave˚ by step scanning between 10° and 70° length k = 1.5406 A in 2h. Optical transmittance spectrum was recorded for the grown crystals in the region 200–3000 nm by 500 Scan UV– Vis–NIR spectrometer. 3. Results and discussion 3.1. Growth of a-form and the effect of NaCl concentration on morphology Morphology of the grown crystals depends very much on the concentration of NaCl in the solution. Photograph of some of the crystals grown from pure aqueous solution is shown in Fig. 2. These have the usual morphology of aglycine with comparatively long growth along the ‘c’ direction than ‘a’. NaCl incorporation changes the actual morphology to the extent that it enhances the growth along the ‘a’ direction and reduces the growth along ‘c’. Because of this, the end morphology of the crystals appears more elongated along ‘a’ direction than that of ‘c’. This morphological change is more when the NaCl concentration increases. Photograph of some of the crystals grown from solution with 5 g NaCl concentration is shown in Fig. 3 for comparison.
Fig. 2. a-Glycine single crystals grown from pure aqueous solution.
Fig. 3. a-Glycine single crystals resulted from solution with 5 g of NaCl concentration in 100 ml of water.
The variation of crystal length along ‘a’ and ‘c’ directions of the grown crystals with NaCl concentration is shown in Fig. 4. This situation continuous until the NaCl concentration has reached a critical level (about 8 g in 100 ml of DD water) in the solution and the crystals resulted out of these solutions are a-form. This is confirmed by XRD. 3.2. Growth of c-form and optimum level of NaCl concentration Above the critical concentration of NaCl (>8 g) the solution yield crystals with different morphology and also belong to c-form. Photograph of some of the crystals resulted from aqueous solution with 8 g NaCl concentration is shown in Fig. 5. The resulted crystals have trigonal end with smooth facets at one end and truncated rough facets on the opposite end, which clearly indicates that the
42
K. Srinivasan, J. Arumugam / Optical Materials 30 (2007) 40–43 15
(110)
13
4000 Counts
Crystal Length (mm)
(210) 11 9
along 'a' along 'c'
7
(200)
2000
(211)
(100)
(400)
(101) 5
(300)
(201)
0 20
30
40
50
60
Position [°2 Theta]
3
Fig. 6. X-ray powder diffraction spectrum of c-glycine.
1 0
1
2
3
4
5
6
7
8
Fig. 4. Variation of crystal length along ‘a’ and ‘c’ directions with NaCl concentration.
Transmittance (%)
Concentration of NaCl (g/100ml of DD Water) 100 90 80 70 60 50 40 30 20 10 0 0
1000
500
1500
2000
2500
Wavalength (nm)
Fig. 7. Optical transmittance spectrum in the UV–Vis–near IR region of the grown c-glycine crystals.
constants of the crystal were determined. The grown c-glycine crystals belong to hexagonal system with space group ˚ and P32 and having lattice parameters a = b = 7.0371 A 3 ˚ ˚ c = 5.4665 A with cell volume 234.44 A . The determined lattice parameter values are in-line with the literature values [4,6]. Fig. 5. c-Glycine single crystals resulted from solution with 8 g of NaCl concentration in 100 ml of water.
crystal has stopped growing at one end and shows only unidirectional growth along its ‘c’ direction. This is a common feature which appears in many highly polar non-linear optical crystals and this behaviour had been reported recently [7]. When the NaCl concentration reached 12 g, the solution yield only crystals with completely destructed morphologies and therefore the optimum level of NaCl concentration to be added to get c-form is about 8–12 g in 100 ml of DD water. 3.3. X-ray powder diffraction study The c-form of these crystals was confirmed by XRD and the spectrum is given in Fig. 6. The recorded powder XRD pattern of a and b forms have showed marked differences as reported in the literature [5,6]. The reflection peaks corresponding to different crystal planes in the XRD spectrum were indexed and from the values of 2h, d-spacing, h k l and relative intensity (I/Io) of every prominent peak, the lattice
3.4. Optical transmittance The recorded optical transmittance spectrum given in Fig. 7 indicates that the grown c-glycine crystals having optical transparency window between 250 and 2600 nm and the lower cut-off wavelength is well below 300 nm in the UV region is the most desirable one for second harmonic generation in this region. 4. Conclusions c-Glycine single crystals were grown from aqueous solutions with NaCl as additives. The incorporation of NaCl in the solution has changed the morphology of the a-glycine significantly. At a critical concentration of NaCl, the solution yield c-glycine crystals. These crystals have unidirectional growth along one of the ‘c’ directions while the growth stops completely along the other ‘c’ direction. The optimum level of NaCl concentration to get c-form is about 8–12 g/100 ml of DD water at room temperature. The form of crystallization was confirmed by X-ray powder diffraction. The grown c-glycine crystals have optical
K. Srinivasan, J. Arumugam / Optical Materials 30 (2007) 40–43
transmittance window in the UV–Vis–near IR region between 250 and 2600 nm. References [1] G. Albrecht, R.B. Corey, J. Am. Chem. Soc. 61 (1939) 1087. [2] Y. Iitaka, Acta Crystallogr. 13 (1960) 35.
[3] [4] [5] [6]
43
Y. Iitaka, Acta Crystallogr. 11 (1958) 225. Y. Iitaka, Acta Crystallogr. 14 (1961) 1. M.N. Bhat, S.M. Dharmaprakash, J. Cryst. Growth 242 (2002) 245. G.L. Perlovich, L.K. Hansen, A. Bauer-Brandl, J. Therm. Anal. Calorim. 66 (2001) 699. [7] K. Srinivasan, J.N. Sherwood, Cryst. Growth Des. 5 (2005) 1359.