Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Structural, spectroscopic, and nonlinear optical investigations on a novel nonlinear optical crystal: Hippuric acid doped ammonium di hydrogen phosphate (HAADP) A. Kumaresh, R. Arun Kumar ⇑ GRD Centre for Materials Research, PSG College of Technology, Coimbatore, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Hippuric acid doped ADP (HAADP)
crystal was grown by solution growth technique for the first time. The crystal is iso-structural with pure ADP with a slight variation in the crystallographic parameters. Both pure ADP and HAADP crystals exhibit a high degree of transparency in the 340–1200 nm region. The functional groups were assigned using FTIR analysis. HAADP crystal possesses 1.5 times SHG efficiency compared with pure ADP.
a r t i c l e
i n f o
Article history: Received 1 September 2013 Received in revised form 23 October 2013 Accepted 31 October 2013 Available online 9 November 2013 Keywords: ADP Growth from solution Powder XRD UV–Vis–NIR FTIR Powder SHG test
a b s t r a c t Transparent single crystals of pure and 1 mol% hippuric acid doped ammonium di hydrogen phosphate (HAADP) were grown from aqueous solution by employing slow evaporation technique. Crystallinity of the grown crystals was studied by powder X-ray diffraction analysis. Both pure ADP and HAADP crystals exhibit tetragonal crystal structure. The bonding structure and molecular associations due to chemical reactions were analyzed by FTIR spectroscopy. It also confirms the functional groups present in the grown crystals. UV–Vis–NIR spectral analysis was carried out to study the optical characteristics of the crystals which reveal that the cutoff wavelength for both pure and hippuric acid doped ADP crystal is around 300 nm. From these spectra it can be clearly inferred that there is an absence of characteristic absorption in the region between 340 and 1200 nm, which is a most desirable property of a material for both SHG and other NLO applications. Second harmonic generation (SHG) test adopting the Kurtz Perry technique revealed that the second harmonic generation efficiency of HAADP is 1.5 times that of pure ADP crystal. Ó 2013 Elsevier B.V. All rights reserved.
Introduction Nonlinear optical (NLO) single crystals are capable of expanding the available spectral region of laser radiation by the process of frequency conversion. Laser radiation in vacuum ultraviolet (VUV) region plays an important role in medical and communication applications [1]. Nonlinear optical crystals can convert laser ⇑ Corresponding author. Tel.: +91 422 4344777; fax: +91 422 2573833. E-mail address: [email protected] (R. Arun Kumar). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.117
frequencies to obtain shorter wavelength laser with high beam stability, at a low cost and with compactness. Many NLO crystals include KH2PO4 (KDP), KTiOPO4 (KTP), LiB3O5 (LBO), b-BaB2O4 (BBO), and CsLiB6O10 (CLBO) and so on, have been developed for device applications [2–5]. However, to develop new NLO crystals with large nonlinear optical coefficients and with high mechanical and chemical stabilities, great efforts are being continuously made by researchers working worldwide. Ammonium di hydrogen phosphate (ADP) with the molecular formula NH4H2PO4 has attracted extensive attention in the investigation of hydrogen bonding
347
A. Kumaresh, R. Arun Kumar / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Fig. 1. Photograph of pure ADP single crystal (a) and photograph of HAADP single crystal (b).
(211)
40
50
60
70
(424)
(440)
(332)
(411)
(220)
30
(510)
(211)
(521)
(a) Pure ADP
(200)
20
(424) (532)
(521)
(224)
(420)
(321) (321)
(004)
(220)
Intensity (a.u)
Good quality single crystals of pure and 1 mol% hippuric acid (HA) doped ADP (HAADP) were grown by solution growth employing slow evaporation technique using de-ionized water as a solvent at 40 °C. For the growth of HA doped ADP crystals, hippuric acid was purified by re-crystallization procedure. 1 mol% HA was added to ADP salt to form a saturated solution. The solution was thoroughly stirred continuously for 5 h for homogenization and then filtered into a Borosil beaker using a Whatmann filter paper. The pH of the solution was maintained as 4.0. The beaker containing the solution (200 ml) was closed with a perforated cover and kept in a dust-free atmosphere. Good quality crystals were harvested within a period of 3–4 weeks with the dimensions 27 mm 8 mm 7 mm for pure ADP and 54 mm 20 mm 11 mm for HAADP crystals. The photographs of pure and 1 mol% HA doped ADP crystals are shown in Fig. 1a and b respectively.
(310)
(b) HA doped ADP
(200)
Single crystal growth
(310)
behaviors in the crystal and the relationship between crystal structure and their properties and it belongs to the isomorphous series of phosphates and arsenates [6]. ADP single crystals still attracts researchers because of its unique properties and plays an important role in second, third and fourth harmonic generation of Nd:YAG and Nd:YLF lasers [7–9]. Intense attention on ADP is directed due to its wide applications as dielectric, piezoelectric, antiferroelectric, electro-optic and nonlinear optical material [10,11]. Below the transition temperature (148.5 K), ADP exhibits antiferroelectric nature with space group P212121 and above the transition temperature it changes its state to paraelectric with space group 1 4 2d [12–13]. The presence of NHþ 4 ions in ADP leads an extra hydrogen bond between N and O [14]. Antiferroelectric interactions between protons are due to the presence of NAH—O hydrogen bond which makes the hydrogen bonds network connecting phosphate groups in ADP crystals. Transition temperature directly depends on NAH—O bond strength. A small change in NAH—O bond strength can change the state of ADP from paraelectric to antiferroelectric [15]. Metal ion impurities can be strongly suppressed by introducing additives to improve the quality of the crystals grown. Oxalic acid and amino acid additives can change the optical, thermal, dielectric and mechanical behavior of ADP crystals to an appreciable extent [16]. Hippuric acid (HA) with the molecular formula C6H5–CO– NH–CH2–COOH is a promising material for second harmonic generation applications because of its high conversion efficiency. It is found in the orthorhombic structure [17,18]. Growth, structural and optical properties of ADP crystal doped with HA is analyzed in this paper. The growth, structural and optical properties of pure ADP and HAADP single crystals are studied and reported.
80
2θ (°) Fig. 2. Powder XRD spectrum of pure ADP crystal (a) and powder XRD spectrum of HAADP crystal (b).
Results and discussion Powder XRD analysis The crystalline quality of the grown crystals and their cell dimensions were studied by powder X-ray diffraction analysis using a Rigaku X-ray diffractometer with Cu Ka radiation source k = 1.540 Å in the 2h range 20–80°. The powder XRD pattern of pure and HAADP crystals are shown in Fig. 2a and b. Using XRDA and unit cell softwares the peaks were indexed and the lattice parameter values of the grown crystals were calculated and listed in Table 1. It is confirmed that the grown crystals belong to scalenohedral class of tetragonal crystal system with the space group 1 4 2d. The incorporation of impurity (hippuric acid) in the crystals gives a slight variation in the lattice parameters and the cell vol-
ume for the doped crystal naturally varies. It is evident for the incorporation of the dopant, unit cell volume gets increased. From the differences observed, it can be inferred that HA has affected the lattice parameters ‘a’ and ‘b’ when compared with ‘c’. X-ray diffraction analysis confirms the presence of impurity in the doped crystals.
FTIR analysis Fourier transform infrared (FTIR) investigations were carried out on the powdered samples of pure and HA doped ADP crystals. The spectrum was observed using a Shimadzu FTIR-8400S spectrometer in the range from 400 to 4000 cm1. The prominent
348
A. Kumaresh, R. Arun Kumar / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Table 1 Unit cell parameters of pure and HA doped ADP crystal. Sample
Lattice parameter
Pure ADP HA doped ADP
35
a = b (Å)
c (Å)
7.4909 7.4993
7.5454 7.5525
(a)
Pure ADP
25 20
4000
3500
2500
2000
1500
551.64
1000
432.05
910.40
1284.59
2875.86
3000
1097.50
5
1446.61
3250.05
10
2399.45 2353.16
15
3109.25
Transmittance (%)
30
Cell volume (Å3)
a = b = c (°)
Structure
423.4015 424.7467
90 90
Tetragonal Tetragonal
peaks in the FTIR pattern have been indexed as shown in Fig. 3a and b. There is a broad envelope between 3700 and 2500 cm1 due to PAOH stretching of H2PO4, OAH stretching of COOH and water of crystallization, NAH stretching of NHþ 3 and CAH stretching of CH2 and CH. Hydrogen bonding interactions of H2 PO 4, COOH and NHþ 3 with adjacent molecules in the crystal are attributed to be the cause for the broadening of the peak [21]. The extra peaks at 1753 cm1, 1604 cm1 and 999 cm1 are due to the impurity atoms of hippuric acid present in the grown HAADP crystal. On comparing the spectra recorded for pure and HAADP crystals, it can be clearly observed that few characteristic absorptions of hippuric acid are present for HAADP crystals. The vibrational frequencies of the functional groups present in the crystals are listed in Table 2. The FTIR analysis confirms the presence of dopants in the grown crystal.
500
Wavenumber (cm-1) 50
(b)
HAADP
UV–Vis–NIR analysis
45
35
5 4000
3500
3000
2500
2000
1500
545.85 445.56
725.23
1000
410.84
10
1753.29
3250.05
15
1099.43 999.13 910.40
20
1604.77 1556.55 1444.68 1411.89 1286.52
2873.94
25
2362.80
30
3103.46
Transmittance (%)
40
500
Wavenumber (cm-1) Fig. 3. FTIR spectrum of pure ADP crystal (a) and FTIR spectrum of HAADP crystal (b).
The purpose of growing pure and HA doped ADP crystals is to employ them in optical applications. Hence, it is important to study the transmission range of the grown crystals. The optical properties of the materials are important, as they provide information on the electronic band structure, localized state and the type of optical transitions because the absorption of UV and visible light involves the promotion of electron in the r and p orbitals from the ground state to higher energy states [19]. The UV–Vis–NIR transmission spectra were recorded using a Jasco V-570 UV–Vis–NIR spectrophotometer in the wavelength range of 200–1200 nm. From the spectra shown in Fig. 4, it is found that the cutoff wavelength of hippuric acid doped ADP crystal is around 300 nm. The absorption below 300 nm is due to the electronic transition occurring in the aromatic ring of C@O group. Around 300 nm, there is a sharp decrease in transmittance due to the absorbance leading to electronic excitation in this region [20]. It can be clearly observed that there is an absence of characteristic absorption in the region between 340 and 1200 nm, which enables the grown crystals for SHG and other NLO applications.
Table 2 Vibrational frequency assignments. Characteristic absorption of pure ADP (cm1)
Characteristic absorption of HAADP (cm1)
Bond assignment
3250, 3109 2875 2399, 2353 ... ... 1446 ... 1284 1097 ... 910 ... 551, 432 ...
3250, 3103 2873 2366 1753 1604 1444 1411 1286 1099 999 910 725 545, 445 410
OAH stretching, PAOAH stretching and, NAH vibrations of ammonium. NAH stretching of ammonium. Combination band vibrations. C@O stretching of COOH. C@C stretching of aromatic group. Bending mode of NH3+ Bending vibrations of ammonium. Combination of asymmetric stretching vibrations of PO4 with lattice PAOAH vibrations. @CAH bending vibrations. PAOAH vibrations. HOAPAOH bending. PO4 vibrations. NAH bending vibrations.
A. Kumaresh, R. Arun Kumar / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Pure ADP HAADP
Transmittance (a.u)
40
20
349
lattice of ADP crystal is slightly distorted due to the addition of HA. UV–Vis–NIR optical analysis shows a superior optical transmittance nature of the crystals in the entire visible region. It is found that the UV cutoff wavelength is around 300 nm and it can be used as a potential material for SHG applications in the visible region, which makes it suitable for laser frequency doubling and related opto-electronic applications. The FTIR study confirms the functional groups present in the grown crystals. Powder SHG studies revealed that both ADP and HAADP crystals are capable of frequency conversion, and the SHG conversion efficiency of HAADP crystals is 1.5 times that of pure ADP crystals. Acknowledgement
0
200
400
600
800
1000
1200
Wavelength (nm) Fig. 4. Transmittance curve of pure ADP and HAADP crystals.
Powder SHG test Powder SHG test by the Kurtz-Perry technique was adopted for the initial testing of the grown crystals for frequency conversion applications [22]. The fundamental beam of wavelength 1064 nm from a Q-switched Nd:YAG laser was used to test the second harmonic generation property of the grown crystals. Pure and hippuric acid doped ADP crystals were ground into fine powders and packed in micro tubes mounted in the path of laser pulses operating with a pulse width of 6 ns and a repetition rate 10 Hz and having an input energy of 0.68 ms/pulse. The second harmonic generation of the crystals was confirmed by a green emission with the of wavelength 532 nm from the samples. The second harmonic generation efficiency of 1 mol% HA doped ADP crystal was found to be 1.5 times that of pure ADP crystals. Conclusion Optically good quality single crystals of pure and hippuric acid (HA) doped ADP crystals were grown by solution growth technique for the first time. The structural characterization of the grown crystals were carried out by powder X-ray diffraction studies which reveals that the tetragonal structure of ADP is preserved and the
One of the authors (R.A) thanks the University Grants Commission (UGC), Hyderabad, India, for providing financial assistance through research project grant. References [1] R. Arun Kumar, R. Dhanasekaran, J. Cryst. Growth 318 (2011) 636–641. [2] H. Furuya, M. Yoshimura, T. Kobayashi, K. Murase, Y. Mori, T. Sasaki, J. Cryst. Growth 198 (199) (1999) 560–563. [3] K. Noda, W. Sakamoto, T. Yogo, S. Hirano, J. Mater. Sci. Lett. 19 (2000) 69–72. [4] C.T. Chen, Y.C. Wu, A.D. Jiang, et al., J. Opt. Soc. Am. B 6 (1989) 616–621. [5] C.T. Chen, B.C. Wu, A.D. Jiang, et al., Sci. Sin. B 28 (1985) 234–243. [6] W.P. Monson, Phys. Rev. 69 (2007) 173. [7] K. Sethuraman, R. Ramesh Babu, R. Gopalakrishnan, P. Ramasamy, J. Cryst. Growth 294 (2006) 349–352. [8] Sunil Chaki, M.P. Deshpanda, Jiten P. Tailor, Mahesh D. Chaudhary, Kunchan Mahato, Am. J. Condens. Matter. Phys. 2 (2012) 22–26. [9] A.P. Voronov, V.I. Salo, V.M. Puzikov, G.N. Babenko, A.D. Roshal, V.F. Tkachenko, J. Cryst. Growth 335 (2011) 84–89. [10] N. Zaitseva, L. Carman, Prog. Cryst. Growth Charact. 43 (2001) 1–118. [11] T. Josephine Rani, Fernando Loretta, P. Selvarajan, S. Ramalingam, S. Perumal, Rec. Res. Sci. Tech. 3 (2001) 69–72. [12] L. Tenzer, B.C. Frozer, R. Pepinsky, Acta. Crystallogr. 11 (1958) 505–509. [13] M.E. Lines, A.M. Glass, Principles and Applications of Ferroelectric and Related Materials, Clarendon Press, Oxford, 1977. [14] A. Jayarama, M.R. Suresh Kumar, S.M. Dharmaprakash, R. Chitra, R.R. Choudhury, Pramana – J. Phys. 71 (2008) 905–910. [15] E. Matsushita, T. Matsubara, J. Phys. Soc. Jpn. 56 (1987) 200–207. [16] M. Yoshimatsu, Jpn. J. Appl. Phys. 5 (1966) 29–35. [17] D.S. Chemla, J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, Orlando, 1987. [18] A. Kumaresh, R. Arun Kumar, Spectrochim. Acta A 111 (2013) 178–181. [19] K. Selvaraju, R. Valluvan, Kumararaman, Mater. Lett. 60 (2006) 2848–2850. [20] R. Ramesh, M. Aravinthraj, M. Selvam, D. Rajkumar, Adv. Appl. Sci. Res. 2 (2011) 136–142. [21] P.V. Dhanaraj, N.P. Rajesh, P. Ramasamy, M. Jayaprakasan, C.K. Mahadevan, G. Bhagavannarayana, Cryst. Res. Technol. 44 (2009) 54–60. [22] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798–3814.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Structural, spectroscopic, and nonlinear optical investigations on a novel nonlinear optical crystal: Hippuric acid doped ammonium di hydrogen phosphate (HAADP) A. Kumaresh, R. Arun Kumar ⇑ GRD Centre for Materials Research, PSG College of Technology, Coimbatore, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Hippuric acid doped ADP (HAADP)
crystal was grown by solution growth technique for the first time. The crystal is iso-structural with pure ADP with a slight variation in the crystallographic parameters. Both pure ADP and HAADP crystals exhibit a high degree of transparency in the 340–1200 nm region. The functional groups were assigned using FTIR analysis. HAADP crystal possesses 1.5 times SHG efficiency compared with pure ADP.
a r t i c l e
i n f o
Article history: Received 1 September 2013 Received in revised form 23 October 2013 Accepted 31 October 2013 Available online 9 November 2013 Keywords: ADP Growth from solution Powder XRD UV–Vis–NIR FTIR Powder SHG test
a b s t r a c t Transparent single crystals of pure and 1 mol% hippuric acid doped ammonium di hydrogen phosphate (HAADP) were grown from aqueous solution by employing slow evaporation technique. Crystallinity of the grown crystals was studied by powder X-ray diffraction analysis. Both pure ADP and HAADP crystals exhibit tetragonal crystal structure. The bonding structure and molecular associations due to chemical reactions were analyzed by FTIR spectroscopy. It also confirms the functional groups present in the grown crystals. UV–Vis–NIR spectral analysis was carried out to study the optical characteristics of the crystals which reveal that the cutoff wavelength for both pure and hippuric acid doped ADP crystal is around 300 nm. From these spectra it can be clearly inferred that there is an absence of characteristic absorption in the region between 340 and 1200 nm, which is a most desirable property of a material for both SHG and other NLO applications. Second harmonic generation (SHG) test adopting the Kurtz Perry technique revealed that the second harmonic generation efficiency of HAADP is 1.5 times that of pure ADP crystal. Ó 2013 Elsevier B.V. All rights reserved.
Introduction Nonlinear optical (NLO) single crystals are capable of expanding the available spectral region of laser radiation by the process of frequency conversion. Laser radiation in vacuum ultraviolet (VUV) region plays an important role in medical and communication applications [1]. Nonlinear optical crystals can convert laser ⇑ Corresponding author. Tel.: +91 422 4344777; fax: +91 422 2573833. E-mail address: [email protected] (R. Arun Kumar). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.117
frequencies to obtain shorter wavelength laser with high beam stability, at a low cost and with compactness. Many NLO crystals include KH2PO4 (KDP), KTiOPO4 (KTP), LiB3O5 (LBO), b-BaB2O4 (BBO), and CsLiB6O10 (CLBO) and so on, have been developed for device applications [2–5]. However, to develop new NLO crystals with large nonlinear optical coefficients and with high mechanical and chemical stabilities, great efforts are being continuously made by researchers working worldwide. Ammonium di hydrogen phosphate (ADP) with the molecular formula NH4H2PO4 has attracted extensive attention in the investigation of hydrogen bonding
347
A. Kumaresh, R. Arun Kumar / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Fig. 1. Photograph of pure ADP single crystal (a) and photograph of HAADP single crystal (b).
(211)
40
50
60
70
(424)
(440)
(332)
(411)
(220)
30
(510)
(211)
(521)
(a) Pure ADP
(200)
20
(424) (532)
(521)
(224)
(420)
(321) (321)
(004)
(220)
Intensity (a.u)
Good quality single crystals of pure and 1 mol% hippuric acid (HA) doped ADP (HAADP) were grown by solution growth employing slow evaporation technique using de-ionized water as a solvent at 40 °C. For the growth of HA doped ADP crystals, hippuric acid was purified by re-crystallization procedure. 1 mol% HA was added to ADP salt to form a saturated solution. The solution was thoroughly stirred continuously for 5 h for homogenization and then filtered into a Borosil beaker using a Whatmann filter paper. The pH of the solution was maintained as 4.0. The beaker containing the solution (200 ml) was closed with a perforated cover and kept in a dust-free atmosphere. Good quality crystals were harvested within a period of 3–4 weeks with the dimensions 27 mm 8 mm 7 mm for pure ADP and 54 mm 20 mm 11 mm for HAADP crystals. The photographs of pure and 1 mol% HA doped ADP crystals are shown in Fig. 1a and b respectively.
(310)
(b) HA doped ADP
(200)
Single crystal growth
(310)
behaviors in the crystal and the relationship between crystal structure and their properties and it belongs to the isomorphous series of phosphates and arsenates [6]. ADP single crystals still attracts researchers because of its unique properties and plays an important role in second, third and fourth harmonic generation of Nd:YAG and Nd:YLF lasers [7–9]. Intense attention on ADP is directed due to its wide applications as dielectric, piezoelectric, antiferroelectric, electro-optic and nonlinear optical material [10,11]. Below the transition temperature (148.5 K), ADP exhibits antiferroelectric nature with space group P212121 and above the transition temperature it changes its state to paraelectric with space group 1 4 2d [12–13]. The presence of NHþ 4 ions in ADP leads an extra hydrogen bond between N and O [14]. Antiferroelectric interactions between protons are due to the presence of NAH—O hydrogen bond which makes the hydrogen bonds network connecting phosphate groups in ADP crystals. Transition temperature directly depends on NAH—O bond strength. A small change in NAH—O bond strength can change the state of ADP from paraelectric to antiferroelectric [15]. Metal ion impurities can be strongly suppressed by introducing additives to improve the quality of the crystals grown. Oxalic acid and amino acid additives can change the optical, thermal, dielectric and mechanical behavior of ADP crystals to an appreciable extent [16]. Hippuric acid (HA) with the molecular formula C6H5–CO– NH–CH2–COOH is a promising material for second harmonic generation applications because of its high conversion efficiency. It is found in the orthorhombic structure [17,18]. Growth, structural and optical properties of ADP crystal doped with HA is analyzed in this paper. The growth, structural and optical properties of pure ADP and HAADP single crystals are studied and reported.
80
2θ (°) Fig. 2. Powder XRD spectrum of pure ADP crystal (a) and powder XRD spectrum of HAADP crystal (b).
Results and discussion Powder XRD analysis The crystalline quality of the grown crystals and their cell dimensions were studied by powder X-ray diffraction analysis using a Rigaku X-ray diffractometer with Cu Ka radiation source k = 1.540 Å in the 2h range 20–80°. The powder XRD pattern of pure and HAADP crystals are shown in Fig. 2a and b. Using XRDA and unit cell softwares the peaks were indexed and the lattice parameter values of the grown crystals were calculated and listed in Table 1. It is confirmed that the grown crystals belong to scalenohedral class of tetragonal crystal system with the space group 1 4 2d. The incorporation of impurity (hippuric acid) in the crystals gives a slight variation in the lattice parameters and the cell vol-
ume for the doped crystal naturally varies. It is evident for the incorporation of the dopant, unit cell volume gets increased. From the differences observed, it can be inferred that HA has affected the lattice parameters ‘a’ and ‘b’ when compared with ‘c’. X-ray diffraction analysis confirms the presence of impurity in the doped crystals.
FTIR analysis Fourier transform infrared (FTIR) investigations were carried out on the powdered samples of pure and HA doped ADP crystals. The spectrum was observed using a Shimadzu FTIR-8400S spectrometer in the range from 400 to 4000 cm1. The prominent
348
A. Kumaresh, R. Arun Kumar / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Table 1 Unit cell parameters of pure and HA doped ADP crystal. Sample
Lattice parameter
Pure ADP HA doped ADP
35
a = b (Å)
c (Å)
7.4909 7.4993
7.5454 7.5525
(a)
Pure ADP
25 20
4000
3500
2500
2000
1500
551.64
1000
432.05
910.40
1284.59
2875.86
3000
1097.50
5
1446.61
3250.05
10
2399.45 2353.16
15
3109.25
Transmittance (%)
30
Cell volume (Å3)
a = b = c (°)
Structure
423.4015 424.7467
90 90
Tetragonal Tetragonal
peaks in the FTIR pattern have been indexed as shown in Fig. 3a and b. There is a broad envelope between 3700 and 2500 cm1 due to PAOH stretching of H2PO4, OAH stretching of COOH and water of crystallization, NAH stretching of NHþ 3 and CAH stretching of CH2 and CH. Hydrogen bonding interactions of H2 PO 4, COOH and NHþ 3 with adjacent molecules in the crystal are attributed to be the cause for the broadening of the peak [21]. The extra peaks at 1753 cm1, 1604 cm1 and 999 cm1 are due to the impurity atoms of hippuric acid present in the grown HAADP crystal. On comparing the spectra recorded for pure and HAADP crystals, it can be clearly observed that few characteristic absorptions of hippuric acid are present for HAADP crystals. The vibrational frequencies of the functional groups present in the crystals are listed in Table 2. The FTIR analysis confirms the presence of dopants in the grown crystal.
500
Wavenumber (cm-1) 50
(b)
HAADP
UV–Vis–NIR analysis
45
35
5 4000
3500
3000
2500
2000
1500
545.85 445.56
725.23
1000
410.84
10
1753.29
3250.05
15
1099.43 999.13 910.40
20
1604.77 1556.55 1444.68 1411.89 1286.52
2873.94
25
2362.80
30
3103.46
Transmittance (%)
40
500
Wavenumber (cm-1) Fig. 3. FTIR spectrum of pure ADP crystal (a) and FTIR spectrum of HAADP crystal (b).
The purpose of growing pure and HA doped ADP crystals is to employ them in optical applications. Hence, it is important to study the transmission range of the grown crystals. The optical properties of the materials are important, as they provide information on the electronic band structure, localized state and the type of optical transitions because the absorption of UV and visible light involves the promotion of electron in the r and p orbitals from the ground state to higher energy states [19]. The UV–Vis–NIR transmission spectra were recorded using a Jasco V-570 UV–Vis–NIR spectrophotometer in the wavelength range of 200–1200 nm. From the spectra shown in Fig. 4, it is found that the cutoff wavelength of hippuric acid doped ADP crystal is around 300 nm. The absorption below 300 nm is due to the electronic transition occurring in the aromatic ring of C@O group. Around 300 nm, there is a sharp decrease in transmittance due to the absorbance leading to electronic excitation in this region [20]. It can be clearly observed that there is an absence of characteristic absorption in the region between 340 and 1200 nm, which enables the grown crystals for SHG and other NLO applications.
Table 2 Vibrational frequency assignments. Characteristic absorption of pure ADP (cm1)
Characteristic absorption of HAADP (cm1)
Bond assignment
3250, 3109 2875 2399, 2353 ... ... 1446 ... 1284 1097 ... 910 ... 551, 432 ...
3250, 3103 2873 2366 1753 1604 1444 1411 1286 1099 999 910 725 545, 445 410
OAH stretching, PAOAH stretching and, NAH vibrations of ammonium. NAH stretching of ammonium. Combination band vibrations. C@O stretching of COOH. C@C stretching of aromatic group. Bending mode of NH3+ Bending vibrations of ammonium. Combination of asymmetric stretching vibrations of PO4 with lattice PAOAH vibrations. @CAH bending vibrations. PAOAH vibrations. HOAPAOH bending. PO4 vibrations. NAH bending vibrations.
A. Kumaresh, R. Arun Kumar / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 346–349
Pure ADP HAADP
Transmittance (a.u)
40
20
349
lattice of ADP crystal is slightly distorted due to the addition of HA. UV–Vis–NIR optical analysis shows a superior optical transmittance nature of the crystals in the entire visible region. It is found that the UV cutoff wavelength is around 300 nm and it can be used as a potential material for SHG applications in the visible region, which makes it suitable for laser frequency doubling and related opto-electronic applications. The FTIR study confirms the functional groups present in the grown crystals. Powder SHG studies revealed that both ADP and HAADP crystals are capable of frequency conversion, and the SHG conversion efficiency of HAADP crystals is 1.5 times that of pure ADP crystals. Acknowledgement
0
200
400
600
800
1000
1200
Wavelength (nm) Fig. 4. Transmittance curve of pure ADP and HAADP crystals.
Powder SHG test Powder SHG test by the Kurtz-Perry technique was adopted for the initial testing of the grown crystals for frequency conversion applications [22]. The fundamental beam of wavelength 1064 nm from a Q-switched Nd:YAG laser was used to test the second harmonic generation property of the grown crystals. Pure and hippuric acid doped ADP crystals were ground into fine powders and packed in micro tubes mounted in the path of laser pulses operating with a pulse width of 6 ns and a repetition rate 10 Hz and having an input energy of 0.68 ms/pulse. The second harmonic generation of the crystals was confirmed by a green emission with the of wavelength 532 nm from the samples. The second harmonic generation efficiency of 1 mol% HA doped ADP crystal was found to be 1.5 times that of pure ADP crystals. Conclusion Optically good quality single crystals of pure and hippuric acid (HA) doped ADP crystals were grown by solution growth technique for the first time. The structural characterization of the grown crystals were carried out by powder X-ray diffraction studies which reveals that the tetragonal structure of ADP is preserved and the
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