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Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals
G Model
ARTICLE IN PRESS
IJLEO 56843 1–4
Optik xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals
1
2
3
4 5 6
Q1
A. Kumaresh a,b , R. Arun Kumar a,b,∗ a b
GRD Centre for Materials Research, PSG College of Technology, Coimbatore, India Department of Physics, PSG College of Technology, Coimbatore, India
7
8 21
a r t i c l e
i n f o
a b s t r a c t
9 10 11 12 13
Article history: Received 21 May 2015 Accepted 17 November 2015 Available online xxx
14
20
Keywords: Crystal growth X-ray diffraction Crystal structure Optical materials Nonlinear optics
22
1. Introduction
15 16 17 18 19
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
Effects of the additions of sodium fluoride (NaF) on the growth, structural and various optical properties of ammonium dihydrogen orthophosphate (ADP) single crystals grown by a slow evaporation solution growth technique from aqueous solution has been investigated. Crystallinity of the grown crystals was studied by powder X-ray diffraction analysis. Both pure and NaF doped ADP crystals exhibit tetragonal crystal structure. 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 NaF doped ADP crystal is around 300 nm. From the spectra it can be clearly inferred that the transmittance percentage is increased in the NaF doped crystals. Also 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. The bonding structure and molecular associations due to chemical reactions were analyzed by FTIR analysis. It also confirms the functional groups present in the grown crystals. Second harmonic generation (SHG) test adopting Kurtz-Perry technique revealed that the second harmonic generation efficiency of NaF doped ADP is 1.3 times that of pure ADP crystal. © 2015 Published by Elsevier GmbH.
Ammonium dihydrogen phosphate (NH4 H2 PO4 ) is widely used as the second, third, and fourth harmonic generator of Nd:YAG and Nd:YLF lasers. The crystals are widely used for electro-optical applications such as Q-switches for Nd:YAG, Nd:YLF, Ti:sapphire and alexandrite lasers, as well as acousto-optical applications [1–4]. Electronic and photonic materials are the key elements for the scientific growth and technological advances in new millennium. The nonlinear optical (NLO) organic materials have been the subject of extensive theoretical and experimental investigations during the past two decades [5,6]. Nonlinear optical (NLO) single crystals are capable of expanding the available spectral region of laser radiation by the process of frequency conversion [7]. Nonlinear optical crystals can convert laser frequencies to obtain shorter wavelength laser with high beam stability, at a low cost and with compactness. Many NLO crystals include KH2 PO4 (KDP), KTiOPO4 (KTP), LiB3 O5 (LBO), -BaB2 O4 (BBO), and CsLiB6 O10 (CLBO) and so on;
have been developed for device applications [8–10]. 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 dihydrogen orthophosphate (ADP) with the molecular formula NH4 H2 PO4 continue to be interesting materials both academically and industrially because it has attracted extensive attention in the investigation of hydrogen bonding behaviors in the crystal and the relationship between crystal structure and their properties and it belongs to the isomorphous series of phosphates and arsenates [11]. Intense attention on ADP is directed due to its wide applications as dielectric, piezoelectric, antiferroelectric, electro-optic and nonlinear optical material [12]. The presence of NH+ ions in ADP leads 4 to an extra hydrogen bond between nitrogen and oxygen [13]. The growth, structural and optical properties of pure and sodium fluoride doped ADP single crystals are studied and reported in this paper. 2. Single crystal growth
∗ Corresponding author at: GRD Centre for Materials Research, PSG College of Technology, Coimbatore, India. Tel.: +91 422 4344777; fax: +91 422 2573833. E-mail address: [email protected] (R. Arun Kumar).
Single crystals of pure and 1 mol% sodium fluoride (NaF) doped ADP were grown by solution growth employing slow evaporation
http://dx.doi.org/10.1016/j.ijleo.2015.11.143 0030-4026/© 2015 Published by Elsevier GmbH.
Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
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70
(a) Pure ADP (b) NaF doped ADP
60
Transmittance (a.u)
50
(b)
40 (a) 30 20 10 0 -10 200
400
600
800
1000
1200
Wavelength (nm)
Fig. 3. (a) Transmittance curve of pure ADP crystal. (b) Transmittance curve of NaF doped ADP crystal.
into a borosil beaker using a Whatmann filter paper. The pH of the solution was noted as 4. 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 28 days with the dimensions 27 mm × 8 mm × 7 mm for pure ADP and 40 mm × 33 mm × 12 mm for NaF doped ADP crystals. The photographs of pure and 1 mol% NaF doped ADP crystals are shown in Fig. 1(a) and (b), respectively.
66 67 68 69 70 71 72
73
20
30
(510)
(303) (204) (323) (224) (321)
40
(521) (440) (305) (424) (116)
(b) NaF doped ADP
(310)
50
60
(424)
(440)
(332)
(510)
(521)
(a) Pure ADP
(411)
(310)
(220)
(211)
(200)
intensity (a.u)
(220)
(321)
(112)
(200)
Fig. 1. (a) Photograph of pure ADP single crystal. (b) Photograph of NaF doped ADP single crystal.
70
80
2θ (°)
Fig. 2. (a) Powder XRD spectrum of pure ADP crystal. (b) Powder XRD spectrum of NaF doped ADP crystal.
3. Results and discussion
74
3.1. Powder XRD analysis
75
Powder X-ray diffraction studies were performed on the grown crystals to analyze the crystalline quality and their cell dimensions using Rigaku X-ray diffractometer with CuK␣ radiation source ˚ in the 2 range 20–80◦ . The powder XRD pattern ( = 1.540 A) of pure and NaF doped ADP crystals is shown in Fig. 2. Using XRDA and unit cell softwares the peaks were indexed and the lattice parameter values of the grown crystals were calculated and are listed in Table 1. It is confirmed that the grown crystals belong to the scalenohedral class of tetragonal crystal system ¯ with the space group I 42d. The incorporation of dopant (sodium fluoride) in the crystals gives a slight variation in the lattice parameters and the cell volume. It is evident for the incorporation of the dopant, the unit cell volume gets decreased. From the differences observed, it can be inferred that NaF has affected the lattice parameters ‘c’ more than ‘a’ and ‘b’. X-ray diffraction analysis confirms the presence of impurity in the doped crystals.
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91
92
60 61 62 63 64 65
technique using de-ionized water as a solvent at room temperature. Analytical reagent grade (AR) samples of ammonium dihydrogen phosphate and sodium fluoride along with distilled water were used for the growth of single crystals. 1 mol% NaF was added to ADP salt to form a saturated solution. The solution was thoroughly stirred continuously for 6 h for homogenization and then filtered
3.2. UV–vis–NIR analysis
93
The purpose of growing pure and NaF 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
Table 1 Unit cell parameters of pure and NaF doped ADP crystals. Sample
Pure ADP NaF doped ADP
Lattice parameter a = b (Å)
c (Å)
7.4909 7.4893
7.5454 7.5233
Cell volume (Å3 )
˛ = ˇ = (◦ )
Structure
423.4015 421.9814
90 90
Tetragonal Tetragonal
Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
94 95 96 97
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IJLEO 56843 1–4
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a 35
Pure ADP
25
15
4000
3500
3000
2500
2000
1500
551 432
910
1284
1097
5
1446
3250
3109
10
2399 2353
20
2875
Transmittance (%)
30
1000
500
3
spectrum was observed using a Shimadzu FTIR-8400S spectrometer in the range from 400 to 4000 cm−1 . The prominent peaks of pure and NaF doped ADP in the FTIR pattern have been indexed as shown in Fig. 4(a) and (b). There is a broad envelope between 3700 and 2500 cm−1 due to P OH stretching of H2 PO4 , O H stretching of water of crystallization and N H stretching of NH+ . Hydrogen 3 + bonding interactions of H2 PO− and NH with adjacent molecules 4 3 in the crystal are attributed to be the cause for the broadening of the peak [15]. The disappearance of 3109 cm−1 peak and extra peak at 1705 cm−1 may be due to the impurity atoms of sodium fluoride present in the grown crystal. The vibrational frequencies of the functional groups present in the crystals are listed in Table 2. The FTIR analysis confirms the presence of functional group in the grown crystal.
115 116 117 118 119 120 121 122 123 124 125 126 127
128
Wavenumber (cm -1 )
b
NaF doped AD P
70
50
10 4000
3500
3000
2500
2000
Wav enumber
555 406
1500
914
3128
1415 1288
20
1097
1705
30
2366
40
2882
Transmittance (%)
60
1000
500
(cm -1 )
Fig. 4. (a) FTIR spectrum of pure ADP crystal. (b) FTIR spectrum of NaF doped ADP crystal.
111
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 and orbitals from the ground state to higher energy states [14]. The UV–vis–NIR absorption and 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. 3(a) and (b), it is found that the cutoff wavelength of sodium fluoride doped ADP crystal is around 300 nm. Transmittance percentage of the NaF doped ADP crystals are much better than pure ADP. 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.
112
3.3. FTIR analysis
98 99 100 101 102 103 104 105 106 107 108 109 110
113 114
Fourier transform infrared (FTIR) investigations were carried out on the powdered samples of pure and NaF doped ADP crystals. The
3.4. 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 [16]. 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 sodium fluoride doped ADP crystals were ground into fine powders and packed in micro tubes mounted in the path of laser radiation operating with a pulse width of 6 ns and at a repetition rate of 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 wavelength 532 nm from the samples. The second harmonic generation efficiency of 1 mol% NaF doped ADP crystal was 1.3 times that of pure ADP crystals.
4. Conclusion Pure and sodium fluoride doped ADP crystals were grown with good transparency and optical quality by solution growth technique. 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 lattice of ADP crystal is slightly distorted due to the addition of NaF. 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 NaF doped ADP crystals are capable of frequency conversion, and the SHG conversion efficiency of NaF doped ADP crystals is 1.3 times that of pure ADP crystals.
Table 2 Vibrational frequency assignments pure and NaF doped ADP crystals. Characteristic absorptions of pure ADP (cm−1 )
Characteristic absorptions of NaF doped ADP (cm−1 )
Bond assignments
3250, 3109 2875 2399, 2353 1446 1284 1097, 910 551, 432 ...
3128 2882 2366 1415 1288 1097, 914 555 406
O H stretching, P O H stretching and, N H vibrations of ammonium. N H stretching of ammonium. Combination band vibrations. Bending mode of NH3+ Combination of asymmetric stretching vibrations of PO4 with lattice P O H vibrations. PO4 vibrations. N H bending vibrations.
Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
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References [1] G. Bhagavannarayana, S. Parthiban, S. Meenakshisundaram, An interesting correlation between crystalline perfection and second harmonic generation efficiency on KCl- and oxalic acid-doped ADP crystals, Cryst. Growth Des. 8 (2) (2008) 446–451. [2] C.S. Strom, L.J.P. Vogels, M.A. Verheijen, Comprehensive computerized survey of the slice configurations of NH4 H2 PO4 (ADP) type structures, J. Cryst. Growth 155 (1995) 144–155. [3] S. Chaki, M.P. Deshpanda, J.P. Tailor, M.D. Chaudhary, K. Mahato, Growth and characterization of ADP single crystal, Am. J. Condens. Matter Phys. 2 (2012) 22–26. [4] A.P. Voronov, V.I. Salo, V.M. Puzikov, G.N. Babenko, A.D. Roshal, V.F. Tkachenko, Hybrid organic–inorganic crystals based on ammonium dihydrogen phosphate and ammonium salicylate, J. Cryst. Growth 335 (2011) 84–89. [5] M.D. Shirsat, S.S. Hussaini, N.R. Dhumane, V.G. Dongre, Influence of lithium ions on the NLO properties of KDP single crystals, Cryst. Res. Technol. 43 (2008) 756–761. [6] R. Mohan Kumar, D. Rajan Babu, D. Jayaraman, R. Jayaval, K. Kitmura, Studies on the growth aspects of semi-organic l-alanine acetate: a promising NLO crystal, J. Cryst. Growth 275 (2005) 1935–1939. [7] R. Arun Kumar, R. Dhanasekaran, Growth and characterization of LCOB and NdLCOB single crystals for laser applications, J. Cryst. Growth 318 (2011) 636–641.
[8] H. Furuya, M. Yoshimura, T. Kobayashi, K. Murase, Y. Mori, T. Sasaki, Crystal growth and characterization of Gdx Y1−x Ca4 O(BO3 )3 crystal, J. Cryst. Growth 198/199 (1999) 560–563. [9] K. Noda, W. Sakamoto, T. Yogo, S. Hirano, Dielectric properties of KTiOPO4 (KTP) single crystals at low temperature, J. Mater. Sci. Lett. 19 (2000) 69–72. [10] C.T. Chen, Y.C. Wu, A.D. Jiang, B.C. Wu, G.M. You, R.K. Li, S.J. Lin, New nonlinearoptical crystal: LiB3 O5 , J. Opt. Soc. Am. B 6 (1989) 616–621. [11] M. Meena, C.K. Mahadevan, Growth and electrical characterization of l-arginine added KDP and ADP single crystals, Cryst. Res. Technol. 43 (2) (2008) 166–172. [12] N. Zaitseva, L. Carman, Rapid growth of KDP-type crystals, Prog. Cryst. Growth Charact. 43 (2001) 1–118. [13] A. Jayarama, M.R. Suresh Kumar, S.M. Dharmaprakash, R. Chitra, R.R. Choudhury, Thiourea-doped ammonium dihydrogen phosphate: a single crystal neutron diffraction investigation, Pramana – J. Phys. 71 (2008) 905–910. [14] K. Selvaraju, R. Valluvan, S. Kumararaman, New nonlinear optical material: glycine hydrofluoride, Mater. Lett. 60 (2006) 2848–2850. [15] P.V. Dhanaraj, N.P. Rajesh, P. Ramasamy, M. Jayaprakasan, C.K. Mahadevan, G. Bhagavannarayana, Enhancement of stability of growth, structural and NLO properties of KDP crystals due to additive along with seed rotation, Cryst. Res. Technol. 44 (2009) 54–60. [16] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical materials, J. Appl. Phys. 39 (1968) 3798–3814.
Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
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ARTICLE IN PRESS
IJLEO 56843 1–4
Optik xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals
1
2
3
4 5 6
Q1
A. Kumaresh a,b , R. Arun Kumar a,b,∗ a b
GRD Centre for Materials Research, PSG College of Technology, Coimbatore, India Department of Physics, PSG College of Technology, Coimbatore, India
7
8 21
a r t i c l e
i n f o
a b s t r a c t
9 10 11 12 13
Article history: Received 21 May 2015 Accepted 17 November 2015 Available online xxx
14
20
Keywords: Crystal growth X-ray diffraction Crystal structure Optical materials Nonlinear optics
22
1. Introduction
15 16 17 18 19
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
Effects of the additions of sodium fluoride (NaF) on the growth, structural and various optical properties of ammonium dihydrogen orthophosphate (ADP) single crystals grown by a slow evaporation solution growth technique from aqueous solution has been investigated. Crystallinity of the grown crystals was studied by powder X-ray diffraction analysis. Both pure and NaF doped ADP crystals exhibit tetragonal crystal structure. 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 NaF doped ADP crystal is around 300 nm. From the spectra it can be clearly inferred that the transmittance percentage is increased in the NaF doped crystals. Also 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. The bonding structure and molecular associations due to chemical reactions were analyzed by FTIR analysis. It also confirms the functional groups present in the grown crystals. Second harmonic generation (SHG) test adopting Kurtz-Perry technique revealed that the second harmonic generation efficiency of NaF doped ADP is 1.3 times that of pure ADP crystal. © 2015 Published by Elsevier GmbH.
Ammonium dihydrogen phosphate (NH4 H2 PO4 ) is widely used as the second, third, and fourth harmonic generator of Nd:YAG and Nd:YLF lasers. The crystals are widely used for electro-optical applications such as Q-switches for Nd:YAG, Nd:YLF, Ti:sapphire and alexandrite lasers, as well as acousto-optical applications [1–4]. Electronic and photonic materials are the key elements for the scientific growth and technological advances in new millennium. The nonlinear optical (NLO) organic materials have been the subject of extensive theoretical and experimental investigations during the past two decades [5,6]. Nonlinear optical (NLO) single crystals are capable of expanding the available spectral region of laser radiation by the process of frequency conversion [7]. Nonlinear optical crystals can convert laser frequencies to obtain shorter wavelength laser with high beam stability, at a low cost and with compactness. Many NLO crystals include KH2 PO4 (KDP), KTiOPO4 (KTP), LiB3 O5 (LBO), -BaB2 O4 (BBO), and CsLiB6 O10 (CLBO) and so on;
have been developed for device applications [8–10]. 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 dihydrogen orthophosphate (ADP) with the molecular formula NH4 H2 PO4 continue to be interesting materials both academically and industrially because it has attracted extensive attention in the investigation of hydrogen bonding behaviors in the crystal and the relationship between crystal structure and their properties and it belongs to the isomorphous series of phosphates and arsenates [11]. Intense attention on ADP is directed due to its wide applications as dielectric, piezoelectric, antiferroelectric, electro-optic and nonlinear optical material [12]. The presence of NH+ ions in ADP leads 4 to an extra hydrogen bond between nitrogen and oxygen [13]. The growth, structural and optical properties of pure and sodium fluoride doped ADP single crystals are studied and reported in this paper. 2. Single crystal growth
∗ Corresponding author at: GRD Centre for Materials Research, PSG College of Technology, Coimbatore, India. Tel.: +91 422 4344777; fax: +91 422 2573833. E-mail address: [email protected] (R. Arun Kumar).
Single crystals of pure and 1 mol% sodium fluoride (NaF) doped ADP were grown by solution growth employing slow evaporation
http://dx.doi.org/10.1016/j.ijleo.2015.11.143 0030-4026/© 2015 Published by Elsevier GmbH.
Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
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2
70
(a) Pure ADP (b) NaF doped ADP
60
Transmittance (a.u)
50
(b)
40 (a) 30 20 10 0 -10 200
400
600
800
1000
1200
Wavelength (nm)
Fig. 3. (a) Transmittance curve of pure ADP crystal. (b) Transmittance curve of NaF doped ADP crystal.
into a borosil beaker using a Whatmann filter paper. The pH of the solution was noted as 4. 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 28 days with the dimensions 27 mm × 8 mm × 7 mm for pure ADP and 40 mm × 33 mm × 12 mm for NaF doped ADP crystals. The photographs of pure and 1 mol% NaF doped ADP crystals are shown in Fig. 1(a) and (b), respectively.
66 67 68 69 70 71 72
73
20
30
(510)
(303) (204) (323) (224) (321)
40
(521) (440) (305) (424) (116)
(b) NaF doped ADP
(310)
50
60
(424)
(440)
(332)
(510)
(521)
(a) Pure ADP
(411)
(310)
(220)
(211)
(200)
intensity (a.u)
(220)
(321)
(112)
(200)
Fig. 1. (a) Photograph of pure ADP single crystal. (b) Photograph of NaF doped ADP single crystal.
70
80
2θ (°)
Fig. 2. (a) Powder XRD spectrum of pure ADP crystal. (b) Powder XRD spectrum of NaF doped ADP crystal.
3. Results and discussion
74
3.1. Powder XRD analysis
75
Powder X-ray diffraction studies were performed on the grown crystals to analyze the crystalline quality and their cell dimensions using Rigaku X-ray diffractometer with CuK␣ radiation source ˚ in the 2 range 20–80◦ . The powder XRD pattern ( = 1.540 A) of pure and NaF doped ADP crystals is shown in Fig. 2. Using XRDA and unit cell softwares the peaks were indexed and the lattice parameter values of the grown crystals were calculated and are listed in Table 1. It is confirmed that the grown crystals belong to the scalenohedral class of tetragonal crystal system ¯ with the space group I 42d. The incorporation of dopant (sodium fluoride) in the crystals gives a slight variation in the lattice parameters and the cell volume. It is evident for the incorporation of the dopant, the unit cell volume gets decreased. From the differences observed, it can be inferred that NaF has affected the lattice parameters ‘c’ more than ‘a’ and ‘b’. X-ray diffraction analysis confirms the presence of impurity in the doped crystals.
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91
92
60 61 62 63 64 65
technique using de-ionized water as a solvent at room temperature. Analytical reagent grade (AR) samples of ammonium dihydrogen phosphate and sodium fluoride along with distilled water were used for the growth of single crystals. 1 mol% NaF was added to ADP salt to form a saturated solution. The solution was thoroughly stirred continuously for 6 h for homogenization and then filtered
3.2. UV–vis–NIR analysis
93
The purpose of growing pure and NaF 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
Table 1 Unit cell parameters of pure and NaF doped ADP crystals. Sample
Pure ADP NaF doped ADP
Lattice parameter a = b (Å)
c (Å)
7.4909 7.4893
7.5454 7.5233
Cell volume (Å3 )
˛ = ˇ = (◦ )
Structure
423.4015 421.9814
90 90
Tetragonal Tetragonal
Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
94 95 96 97
G Model
ARTICLE IN PRESS
IJLEO 56843 1–4
A. Kumaresh, R. Arun Kumar / Optik xxx (2015) xxx–xxx
a 35
Pure ADP
25
15
4000
3500
3000
2500
2000
1500
551 432
910
1284
1097
5
1446
3250
3109
10
2399 2353
20
2875
Transmittance (%)
30
1000
500
3
spectrum was observed using a Shimadzu FTIR-8400S spectrometer in the range from 400 to 4000 cm−1 . The prominent peaks of pure and NaF doped ADP in the FTIR pattern have been indexed as shown in Fig. 4(a) and (b). There is a broad envelope between 3700 and 2500 cm−1 due to P OH stretching of H2 PO4 , O H stretching of water of crystallization and N H stretching of NH+ . Hydrogen 3 + bonding interactions of H2 PO− and NH with adjacent molecules 4 3 in the crystal are attributed to be the cause for the broadening of the peak [15]. The disappearance of 3109 cm−1 peak and extra peak at 1705 cm−1 may be due to the impurity atoms of sodium fluoride present in the grown crystal. The vibrational frequencies of the functional groups present in the crystals are listed in Table 2. The FTIR analysis confirms the presence of functional group in the grown crystal.
115 116 117 118 119 120 121 122 123 124 125 126 127
128
Wavenumber (cm -1 )
b
NaF doped AD P
70
50
10 4000
3500
3000
2500
2000
Wav enumber
555 406
1500
914
3128
1415 1288
20
1097
1705
30
2366
40
2882
Transmittance (%)
60
1000
500
(cm -1 )
Fig. 4. (a) FTIR spectrum of pure ADP crystal. (b) FTIR spectrum of NaF doped ADP crystal.
111
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 and orbitals from the ground state to higher energy states [14]. The UV–vis–NIR absorption and 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. 3(a) and (b), it is found that the cutoff wavelength of sodium fluoride doped ADP crystal is around 300 nm. Transmittance percentage of the NaF doped ADP crystals are much better than pure ADP. 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.
112
3.3. FTIR analysis
98 99 100 101 102 103 104 105 106 107 108 109 110
113 114
Fourier transform infrared (FTIR) investigations were carried out on the powdered samples of pure and NaF doped ADP crystals. The
3.4. 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 [16]. 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 sodium fluoride doped ADP crystals were ground into fine powders and packed in micro tubes mounted in the path of laser radiation operating with a pulse width of 6 ns and at a repetition rate of 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 wavelength 532 nm from the samples. The second harmonic generation efficiency of 1 mol% NaF doped ADP crystal was 1.3 times that of pure ADP crystals.
4. Conclusion Pure and sodium fluoride doped ADP crystals were grown with good transparency and optical quality by solution growth technique. 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 lattice of ADP crystal is slightly distorted due to the addition of NaF. 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 NaF doped ADP crystals are capable of frequency conversion, and the SHG conversion efficiency of NaF doped ADP crystals is 1.3 times that of pure ADP crystals.
Table 2 Vibrational frequency assignments pure and NaF doped ADP crystals. Characteristic absorptions of pure ADP (cm−1 )
Characteristic absorptions of NaF doped ADP (cm−1 )
Bond assignments
3250, 3109 2875 2399, 2353 1446 1284 1097, 910 551, 432 ...
3128 2882 2366 1415 1288 1097, 914 555 406
O H stretching, P O H stretching and, N H vibrations of ammonium. N H stretching of ammonium. Combination band vibrations. Bending mode of NH3+ Combination of asymmetric stretching vibrations of PO4 with lattice P O H vibrations. PO4 vibrations. N H bending vibrations.
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Please cite this article in press as: A. Kumaresh, R. Arun Kumar, Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals, Optik - Int. J. Light Electron Opt. (2015), http://dx.doi.org/10.1016/j.ijleo.2015.11.143
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