Accepted Manuscript Structural, optical, thermal and mechanical properties of Urea tartaric acid single crystals P. Vinothkumar, K. Rajeswari, R. Mohan Kumar, A. Bhaskaran PII: DOI: Reference:

S1386-1425(15)00236-X http://dx.doi.org/10.1016/j.saa.2015.02.063 SAA 13365

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

1 September 2014 16 February 2015 17 February 2015

Please cite this article as: P. Vinothkumar, K. Rajeswari, R. Mohan Kumar, A. Bhaskaran, Structural, optical, thermal and mechanical properties of Urea tartaric acid single crystals, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.02.063

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Structural, optical, thermal and mechanical properties of Urea tartaric acid single crystals P. Vinothkumar, K. Rajeswari, R. Mohan Kumar, A. Bhaskaran* Department of Physics, Presidency College, Chennai – 600 005, India. Abstract Urea tartaric acid (UT) an organic nonlinear optical (NLO) material was synthesized from aqueous solution and the crystals were grown by the slow evaporation technique.The single crystal X-ray diffraction (XRD) analysis revealed that the UT crystal belongs to the orthorhombic system. The functional groups of UT have been identified by the Fourier transform infrared spectral studies. The optical transparent window in the visible and near the IR regions was investigated. The transmittance of UT has been used to calculate the refractive index (n) as a function of the wavelength. The nonlinear optical property of the grown crystal has been confirmed by the Kurtz powder second harmonic generation test. The birefringence of the crystal was determined using a tungsten halogen lamp source. The laser induced surface damage threshold for the grown crystal was measured using the Nd:YAG laser. The anisotropic in mechanical property of the grown crystals was studied using Vicker’s microhardness tester at different planes. The Etch pit density of UT crystals was investigated. The thermal behavior of UT was investigated using the TG-DTA and DSC studies. Keywords: Solubility, X-ray diffraction, Recrystallization, Single crystal growth, Nonlinear optical material *Corresponding author:

Dr. A. BHASKARAN Department of Physics, Presidency College Chennai-600 005, India. Tel: +91 9840800250,Fax: +91-44-2235 2870 Email:[email protected]

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1. Introduction Organic materials like DAST, Urea and p-hydroxybenzoic acid exhibit large nonlinear susceptibilities, due to π-conjugation and molecular electronic properties[1]. Urea crystal belongs to the tetragonal crystal system with a needle like shape. The polar properties of Urea molecules contribute to their nonlinear optical characteristics, but at the same time, contribute strongly to an anisotropic growth. The Urea crystal possesses large nonlinearities, very good transparency up to 200 nm and large birefringence. Hence, it is a useful material for the processes of generation and mixing of frequencies, in a large range of the spectrum including UV [2-4]. However, the hygroscopic nature of Urea constrains its usage in growth processes and devices. Urea derivatives can be considered as important materials because of their nonlinearities, optical transparency, adequate birefringence and environmental stability. The Urea molecule is planar in crystal structure and the oxygen atom of Urea has more electronegativity compared to the nitrogen atom due to the lone pair of N atoms with π-electron on carbonyl results, causing a decrease in the electron density around the N atoms. Due to the charge transfer among the C, H and N molecules, the H+ ions become weaker and O- become stronger. Complex formation with Urea is possible in two ways. One through the N molecule, and the other through the O atom, which leads to ionic and addict complexes respectively. The chiral molecule or carboxylic acid binds with the O of Urea through O-H and forms many addiction complexes. Urea tartaric acid is an additive compound formed by small organic molecules of Urea and the chiral molecule of L-tartaric acid. The crystal structure of UT is stabilized by a strong hydrogen bond (O-H⋅⋅⋅O) in three dimensional networks, between Urea and tartaric acid. The short O-H ⋅⋅O interactions of Urea and tartaric acid molecules can lead to an inclusion complex with non-centrosymmetrical structure.

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The UT crystal is more rigid and is expected to enhance the optical nonlinearity due to cross linking of multidirectional hydrogen bonds or multi bond character in C-N and C- O bonds [5-6]. In this paper, the synthesis, growth and characterizations, such as X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), UV-Vis-NIR spectroscopy studies, second harmonic generation (SHG),

birefringence, thermal and laser damage

threshold studies of the UT crystal have been investigated and reported.

2. Experimental Details 2.1 Synthesis The Urea and L-tartaric acid were taken in 1:1 molar ratio and dissolved in methanol separately at 40 °C and 35 °C respectively. The solutions were stirred well for 4 h, and a clear solution was obtained. The prepared two solutions were mixed at 45 °C and the hot solution was allowed to cool at 30 °C using constant temperature bath. After 10 days, the white precipitation of Urea tartaric acid compound was formed as per the following reaction.

CO (NH2)2 + C4H6O6

C4H6 O6 · CH4N2 O

The chemical composition of the UT compound determined using Perkin Elmer result analyser reveals that it contains 28.63% carbon (28.71 %), 4.74% hydrogen (4.79 %), 13.32% nitrogen (13.33%) where the figures in bracket represent the theoretical composition. These values are well agreed with calculated values Urea tartaric acid compound.

2.2 Crystal growth The solution was left for slow evaporation, resulting in the formation of a compound of white microcrystalline organic salt. The synthesized salt was then purified by repeated recrystallization process using deionised water.The solubility of UT in deionised water was

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determined in the temperature range of 30-55°C as illustrated in Fig.1. The solubility curve reveals that the synthesized compound displays a positive temperature gradient of solubility. A saturated solution of the UT compound was prepared at 40°C in an aqueous solution at pH 3 and kept in constant temperature bath for slow evaporation. Transparent UT crystals of average dimension 12×4×5 mm3 were obtained, after a typical growth period of 45 days, as shown in Fig.2. The grown crystal was stable in the environment without sacrificing its transparency.

3. Results and discussion 3.1. X-ray diffraction and Morphology studies The X-ray diffraction data was collected for a well-shaped single crystal of UT using a CAD-4, Enraf Nonius-FR590 automatic X-ray diffractometer, with MoKα (λ = 0.7170Å) radiation. The reflections from a finite number of planes were collected. It was observed that the crystal belongs to the orthorhombic system, with the following cell dimensions: a = 5.072 (3) Å, b= 9.792 (2) Å and c = 17.231 Å with unit cell volume V = 855.77Å3 and space group P212121. The observed lattice parameter values are closely in agreement with the reported values [7], confirming the identity of the grown crystal. The typical morphology of the UT crystal is depicted in Fig. 3. It was observed that the crystal has four prominent morphological faces, namely (230), (1 0 0), (0 1 0), and (0 0 1) with a-axis along the length of the crystal. Among them, (0 1 0), (0 0 1) are the thinnest crystallographic planes. The unit cell has the shortest dimension along the a-axis. It was inferred that the fastest growth of the crystal occurs along the shortest crystallographic axis [8].

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3.2. FT-IR studies The FT-IR spectral analysis was carried out to identify the chemical bonding and molecular structure of the material. The FT-IR spectrum of UT was recorded using a BrukerIFS-66V spectrophotometer in the region 400–4000cm-1, by KBr pellet technique. The FTIR spectrum of UT single crystal is shown in Fig. 4. The peaks at 3373 and 3329 cm-1 are due to the asymmetric stretching and symmetric stretching vibrations of the N–H group respectively. The peak at 3266 cm-1 is attributed to OH symmetric stretching. The peaks at 2832, 2492 and 1702 cm-1 are assigned to C-H asymmetric stretching, C-H symmetric stretching and C=O asymmetric stretching respectively. The presence of C=O of Urea is evident from the strong and sharp peak at 1608 cm-1. The band at 1010 cm-1 is attributed to N-C-N symmetric stretching. The N-C-N asymmetric stretching was observed at 1401 cm-1. The peak at 813 cm-1 is due to C-C bending. The bond of carbon atom among the other atoms of Urea as a whole, exhibits out of plane bending and appears as a sharp band at 793 cm-1. The observed wave numbers and the assignments of the UT compound are given in Table 1.

3.3. UV-Vis–NIR Spectroscopic studies The transmittance spectrum of the UT crystal having a 2 mm thick on (230) plane was recorded in the wavelength range 200 – 1200 nm, using Varian Cary 5E UV–Vis NIR spectrophotometer. The recorded UV-visible spectrum is shown in Fig. 5. It was observed that the UT crystal is transparent in the entire visible region without any absorption peak. The cut-off wavelength occurs at 240 nm, suggesting that UT is capable of producing second harmonic generation (SHG) and third harmonic generation (THG), without any significant absorption.

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The optical absorption coefficient (α) was calculated using the following relation,
=

.  ( /) 

(1)

where T is the transmittance and t is the thickness of the crystal. The optical band gap and absorption coefficient are related using the relation,

(αhυ) =A (hυ-Eg)1/2

(2)

where Eg is the optical band gap and A is a constant. The extinction coefficient (K) was obtained in terms of the absorption coefficient,

=

 

(3)

where λ is the wave length of radiation. The reflectance (R) in terms of the absorption coefficient was calculated using the relation,

R=

()±()()()   () !()

(4)

The linear refractive index (n) was calculated and found to be 1.44 at λ =800 nm, using the relation, √)

" = −(R + 1) ± 2' () ) (5) The band gap of the UT crystal was estimated by plotting (ahv) 2 versus hv, as shown in Fig.(6). The band gap value was estimated by extrapolating the linear portion near the onset of the absorption edge to the energy axis, and it was found to be 4.9 eV. This high band gap value indicates that the grown crystal possesses a dielectric behavior, to induce polarization when powerful radiation is incident on the material [9].

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3.4. Second harmonic generation (SHG) and phase matching property The Kurtz powder technique is the most widely used method on powder sample to ascertain the nonlinearity and phase matchable nature. The particles of different sizes were prepared by sieving the powdered UT samples. The amount of SHG from the various sizes of the particles was measured, and the graph was plotted between the SHG output and particle size, as shown in Fig. 7. From the Figure, it was observed that initially, SHG output increases as the particle size increases, when the average particle size is less than the coherence length (a propagation distance over which electromagnetic waves maintain ordering) of the medium. For a particular particle size, the SHG output reaches the maximum value, and there after, it saturates and maintains a constant value. It was reported, that once the particle size attains the coherence length, SHG reaches saturation. The SHG output due to a correctly oriented particle balances the loss in SHG due to the decrease in the number of particles, causes SHG remains constant after saturation. The SHG output as a function of particle size confirmed the phase-matchable nature of the UT crystal[10]. The SHG output efficiency of UT was compared with KDP and Urea. The average powder SHG efficiency was found to be three times greater than that of KDP and 0.95 times of Urea. The particle dependence SHG nature of Urea, UT and KDP powders are given in Table 2.

3.5. Birefringence studies A birefringence study was carried out on (230) plane of the polished UT, crystal having a thickness of 1.94 mm. The improvised channel spectrum method was employed to investigate the birefringence value. A 1000 W tungsten halogen lamp was used as a source, the collimated light was allowed to incident on the UT crystal, placed between the polarizer

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and analyser. The transmitted light from the analyser under goes interference and produces a fringe pattern. The birefringence was calculated using the relation,

∇" =

, 

(6)

where λ is the wavelength, t is the thickness of the crystal, and k is the fringe order. The graph was drawn between the wavelength and birefringence, as shown in Fig.8. The curve indicates that birefringence decreases as the wavelength increases and the birefringence values lie between 0.0745 and 0.0686 for the wavelength region 450–650 nm. The small variation of birefringence for a wide range of wavelength proves that the UT crystal is highly suitable for second harmonic generation. The birefringence studies also ensure that the optical axis of the UT crystal lies along the c or z direction. The comparison of the birefringence values of the UT crystal with the other NLO single crystals, is given in Table 3.

3.6 Laser-induced damage threshold study Laser induced damage is one of the most important parameters in the choice of a material for NLO application. The laser damage threshold depends on a number of laser parameters, such as wavelength, energy, pulse duration, longitudinal and transverse mode structures, beam size, location of the beam, etc. [14]. A Q-switched Nd:YAG laser operating in TEM00 mode was used as the source at 532 nm, pulse width of 6 ns and repetition rate of 5 Hz. The sample was placed at the focus of a plano convex lens of focal length 30 cm and laser beam of diameter 1mm was focused on the crystal. An attenuator was used to vary the energy of the laser pulses with a polarizer and a half wave plate. The pulse energy of each shot was measured using the combination of a phototube and an oscilloscope.

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The surface damage threshold of the crystal was calculated using the expression; Powder density (Pd) = E / τπr2 W/cm2

(7)

where E is the energy (mJ), τ is the pulse width (ns) and r is the radius of the spot (mm). The measured single shot laser damage threshold valueis 4.6 GW/cm2 at 532 nm wavelength. The laser damage threshold values of UT with some NLO organic and inorganic single crystals are compared, and given in Table 4.

3.7. Microhardness studies

Microhardness is one of the important parameters, studied before any crystal is considered as suitable for device application. The hardness of a material is a measure of its resistance to plastic deformation [17]. The microhardness measurement of UT was recorded at room temperature, using the Economet (Model VH1MD) hardness tester, with Vicker’s pyramidal diamond indenter. The UT crystal was held firmly by forming a mould. A diamond indenter was pressed into the selected surface of the grown UT crystal for the applied load from10 to100 g and a dwell time of 10 s. The Vicker’s microhardness was estimated using the relation, Hv = 1.8544 P/d2

(kg/mm2)

(8)

where, Hv is the Vicker’s hardness number, P is the indentation load in kg and d is the diagonal length of the impressions in mm. A graph has been plotted between the hardness number (Hv) and applied load (P) for the corresponding planes,as shown in Fig.9. It is evident from the graph that the microhardness of the crystal increases with the increase in applied load due to weak bonding forces among the molecules of UT crystals. For all the planes, the same trend was observed. The increase in the microhardness with increasing load is in agreement with the reverse indentation size effect. 9

The measured hardness number was found to be higher for (2 3 0) plane as compared to the other planes (1 0 0), (0 1 0) and (0 0 1). The work hardening coefficient of the UT crystal was estimated using the Meyer’s relation, P =adn

(9)

log P = log k + n log d

(10)

where k is the material constant and ‘n’ is the Meyer's index. Thework hardening coefficient was calculated from the plot of log P versus logd, by the least-square fit method [18] as shown in Fig.10. The values of n obtained for (230), (1 0 0), (010) and (0 0 1) planes of the grown UT crystal are found to be above 1.6. These values indicates that UT belongs to the soft material category.

3.8. Etching studies

The knowledge of defects in crystals is important, because they have adverse effects on the performance of devices and plays an important role in crystal growth. The (230), (1 0 0), (0 1 0) and (0 0 1) planes of the grown UT crystals were subjected to etching, using water at room temperature with a time of 5 s each, separately. The observed etch pit pattern for (230) plane is shown in Fig.11. The rectangular shaped etch pits were observed in all the planes and found more number of etch pits. On successive etching, the etch time was increased to 10 s, 20 s, the pattern remains the same, but the sizes of the etch pits increases. It was observed that, the etch pit does not disappear, in all the cases suggesting that the etch pits are due to dislocations[19]. The etch pit density for the UT crystal on (230) plane was calculated and it was found to be 2.4x104/cm2.

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3.9. Thermal studies. Thermo gravimetric and differential scanning calorimetric analyses for UT have been done, using a thermal analyser PL-STA 1500. A ceramic crucible was used for heating the sample, and the measurements were carried out in nitrogen atmosphere, at a heating rate of 20°C/min in the temperature range 30–500°C. The TG-DTA and DSC curves of UT are illustrated in Fig.12-13. The initial mass of the UT sample subjected to the thermal analyser was 1.5 mg, and the final mass after the experiment was only 20 % of the initial mass, at a temperature of about 150 °C indicating a bulk decomposition of UT in the temperature range 124 – 169 °C, the volatile elements detached from the coordinating sphere, resulting in major weight loss about 70.69 % and it is due to liberation of various gaseous fractions like carbon dioxide, carbon monoxide and NH3. The weight loss 70.89 % is very close to the theoretical weight loss of molecules comprising CO2, CO and NH3. The major weight loss that appears in TGA curve is also reflected from second endothermic peak of DTA curve. Above 170 °C, the residual elements were in the form of hydrocarbons, resembling C2H4O2. From the DSC curve, the melting point of the material was observed at 102 °C. The sharpness of exothermic peak showed the existence of a good degree of crystallinity and purity of the sample. Further, it indicates that there exists no phase transition before this temperature.There is a gradual and significant weight loss, as the temperature is increased above the melting point. The DTA endothermic peak observed at 105 °C corresponds to the melting point of the UT compound. The DTA peak is coincide with DSC curve. The melting point of the UT compound was determined using a melting point apparatus as 102 ±1°C and it is agreed with DSC and DTA curves. The presence of water of crystallization in the UT compound is not observed. Hence from TGA, DTA and DSC thermal studies the UT crystal belongs to non-hydrated nature.The TG analysis of UT reveals that the crystal is stable up to 116 °C in N2 atmosphere. The DSC infers that the UT sample melts at 102°C.

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4. Conclusion Single crystals of the organic NLO UT material, were grown from deionised water by slow evaporation technique. The unit cell parameters and morphology of UT were evaluated by single crystal XRD. The functional groups of UT compound was analysed using FTIR spectrum. The UV–Vis–NIR spectrum shows that UT is a promising candidate for the tuneable lasers in the range 350–1200 nm. The good optical transmittance in the entire visible region makes the crystal a potential candidate for optoelectronic applications.The powder SHG efficiency of UT is 3.2 times greater than that of KDP and 0.95 times to Urea crystal; the particle size dependency of second harmonic intensity demonstrated the existence of the phase matching property of the UT crystal. The birefringence of UT was evaluated, and the values were found to be 0.0745 and 0.0686 for the wavelength region 450–650 nm. The laser induced surface damage threshold was measured as 4.6 GW/cm2 at 530 nm. The anisotropic nature of the UT crystal was confirmed by the microhardness studies, and work hardening coefficient of UT confirms that it is a soft crystal type. The dislocation density was estimated from the etching studies. The thermal studies revealsthat the UT single crystal was thermally stable up to116°C.

Acknowledgement One of the authors (P.V) is grateful to the University Grants Commission (UGC), Government of India, for the award of the Project Fellow under the Major Research Project (F.NO.41/936/2012 (SR).

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References [1] D.S. Chemla and J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, New York, USA, 1987. [2] M. Ebrahimzadeh, M.H. Dunn, F. Akerboom, Opt. Lett., 14 (1989) 560-562. [3] D.J. Halfpenny, J.N. Sherwood, Philos. Mag. Lett., 62 (1990) 1-7. [4] J. Zyss, J. Non. Crystalline Solids, 47 (1982) 211-226. [5] W. Yu, M. Lu, F. Meng, Mater. Res. Bull., 31 (1996) 1127-1131. [6] W. Yu, M. Lu, F. Meng, Mater. Res. Bull., 31 (1996) 1121-1125. [7] F.Q. Meng, M.K. Lu, H. Zen, Cryst. Res.Tech., 31 (1996) 33-36. [8] A.S.H. Hameed, P. Anandan, R. Jayavel, P. Ramasamy, G. Ravi, J. Cryst.Growth 249 (2003) 316-320. [9] P. A. Henikhena, African Phys.Rev., (2008) 68-77. [10] S.K. Kurtz, T.T. Perry, J. Appl. Phys., 36 (1968) 3798-3813. [11] M. Senthil Pandian, P. Ramasamy, Mater. Chem. Phys., 132 (2012) 1019-1028. [12] M. Senthil Pandian, K. Boopathi, P. Ramasamy, G. Bhagavannarayana, Mater. Res. Bull., 47 (2012) 825-826. [13] N. Renuka, N. Vijayan, B. Rathi, R. Ramesh Babu, K. Nagarajan, D. Haranath, G. Bhagavannarayana, Optik 123 (2012) 189-192. [14] N. Vijayan, G. Bhagavannarayana, T. Kanagasekaran, R. Ramesh Babu, R. Gopalakrishnan, P. Ramasamy, Cryst. Res. Technol. 41 (2006) 784-789. [15] S.A. Martin Britto Dhas, S. Natarajan, Cryst. Res. Technol. 42 (2007) 471-476. [16] S.A. Martin Britto Dhas, M. Suresh, G. Bhagavannarayana, S. Natarajan, J. Cryst. Growth 309 (2007) 48-52. [17] K. G. Subhadra, K. Kishan Rao, D. B. Sirdeshmukh, Bull. Mater Sci., 23 (2000) 147–150.

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[18] E. M. Onitsch, Mikroscopia., 2 (1947) 131–134. [19] K. Kishnan Rao, V. Surender, Bull. Mater.Sci., 24 (2001) 665-669.

Figure captions Fig.1 Solubility curve of UT crystal Fig.2 As grown UT crystal Fig.3 Morphology of UT crystal Fig.4 FTIR spectrum of UT crystal Fig.5 UV-Vis-NIR spectrum of UT crystal Fig.6 Plot of Photon energy vs. (αhν)2 of UT crystal Fig.7 Phase matching curve of UT crystal Fig.8 Plot of Wavelength vs. birefringence of UT crystal Fig.9 Load (P) vs. hardness number (Hv) of UT crystal Fig.10 Plot of between log P versus log d of UT crysal Fig.11 Etch pattern of UT crystal Fig.12 TGA and DSC curves of UT crystal Fig.13 TGA and DTA curves of UT crystal

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Table Captions

Table 1 The observed wave numbers and the assignments of UT crystal Table 2 Comparison of particle dependence SHG of Urea, UT, KDP crystals Table 3 Comparison of birefringence value of UT with some NLO crystals Table 4 Comparison of Laser damage threshold value of UT crystal with some inorganic, organic and semi organic crystals

15

Solubility (g/100 ml )

65

60

55

50

30

35

40

Temperature (°C)

Fig.1

16

45

50

Fig.2

17

Fig.3

18

Fig.4

19

60

Transmittance (%)

50

40

30

20

10

0 200

400

600

800

Wave length (nm)

Fig.5

20

1000

1200

1.40E+009 1.20E+009

8.00E+008 6.00E+008

2

(αhυ ) (eV/m)

2

1.00E+009

4.00E+008 2.00E+008 0.00E+000 1

2

3

4

5

Photon energy hυ (eV)

Fig.6

21

6

7

140

SHG output (mV)

120

UREA KDP UT

100 80 60 40 20 0 below 100

100-124

125-149

Particle size (µm)

Fig.7

22

150 above

Fig.8

23

(230) (1 0 0 ) ( 0 1 0) (001)

110

2

Hardness Number HV (kg /mm )

120

100 90 80 70 60 50 20

40

60

Load P (g)

Fig.9

24

80

100

(2 3 0 ) (1 0 0 ) (0 1 0) (0 0 1)

1.7

log d

1.6

1.5

1.4

1.3

1.2 1.0

1.2

1.4

log P (g)

Fig.10

25

1.6

1.8

2.0

Fig.11

26

Weight (%)

20

80

15

60

10

40

5

20

0

0

100

200

Temperature (°C)

Fig.12

27

300

400

DSC Heat flow (mW)

TGA DSC

100

TGA DTA

100

4 2 0

Weight (%)

-2 -4

60 -6 -8

40

-10 -12

20

-14 100

200

300

Temperature (°C)

Fig.13

28

400

Microvolt Endo Down (µV)

80

Table 1

Wavenumber (cm-1)

Assignments

3373

N-H asymmetric stretching

3329

N-H symmetric stretching

3266

OH symmetric stretching

2832

C-H asymmetric stretching

2492

C-H symmetric stretching

1702

C=O asymmetric stretching

1608

C=O asymmetric stretching

1401

C-O asymmetric stretching

1308

C-H bending

1263

C-C stretching

929

C-O bending

813

C-C bending

29

Table 2

Crystal

Particle size (µm) and SHG output (mV) Below 100

100-124

125-150

Urea

105

125

129

141

KDP

33

40

41

45

Urea tartaric acid

100

122

126

139

30

above 150

Table 3

Crystal

Birefringence value

Sodium sulfanilate dihydrate

0.0260 a

Benzophenone

0.0235b

L-Arginine acetate

0.04325c

Urea tartaric acid

0.0736 d*

a

Ref [11], bRef [12], cRef [13], d*Present work.

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Table 4 Laser damage threshold (GW/cm2)

Crystal Urea

1.5a

Benzimidazole

2.9a

L-Prolinium tartrate

5.9 b

L-Tartaric acid

5.4c

Urea tartaric acid

4.6 e*

a

Ref [14], bRef [15], cRef [16], e*Present work

32

Graphical abstract

33

Highlights:


Urea tartaric acid crystal has been grown by slow evaporation technique.




Optical band gap of UT was estimated using UV-Vis-NIR spectral data.




SHG efficiency of UT was found to be 3.2 times that of KDP and close to urea.




Birefringence values of UT were measured as a function of wavelength.




Laser damage threshold value of UT was determined using Nd : YAG laser.

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