Growth, spectral, thermal, laser damage threshold, microhardness, dielectric, linear and nonlinear optical properties of an organic single crystal: L-phenylalanine DL-mandelic acid

Author’s Accepted Manuscript Growth, spectral, thermal, laser damage threshold, microhardness, dielectric, linear and nonlinear optical properties of an organic single crystal: LPhenylalanine DL-Mandelic acid P. Jayaprakash, M. Peer Mohamed, P. Krishnan, M. Nageshwari, G. Mani, M. Lydia Caroline www.elsevier.com/locate/physb

PII: DOI: Reference:

S0921-4526(16)30418-5 http://dx.doi.org/10.1016/j.physb.2016.09.010 PHYSB309633

To appear in: Physica B: Physics of Condensed Matter Received date: 26 July 2016 Revised date: 8 September 2016 Accepted date: 10 September 2016 Cite this article as: P. Jayaprakash, M. Peer Mohamed, P. Krishnan, M. Nageshwari, G. Mani and M. Lydia Caroline, Growth, spectral, thermal, laser damage threshold, microhardness, dielectric, linear and nonlinear optical properties of an organic single crystal: L-Phenylalanine DL-Mandelic acid, Physica B: Physics of Condensed Matter, http://dx.doi.org/10.1016/j.physb.2016.09.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Growth, spectral, thermal, laser damage threshold, microhardness, dielectric, linear and nonlinear optical properties of an organic single crystal: LPhenylalanine DL-Mandelic acid P. Jayaprakasha, M. Peer Mohameda, b, P. Krishnanc, M. Nageshwaria, G. Mani a,

M.

Lydia Caroline,a,* a

PG & Research Department of Physics, Arignar Anna Govt. Arts College, Cheyyar - 604 407, TamilNadu,

India b

Department of Physics, C. Abdul Hakeem College, Melvisharam – 632 509,TamilNadu, India

c

Department of Physics, St. Joseph’s College of Engineering, Chennai-600 119, TamilNadu, India

Abstract Single crystals of L-phenylalanine dl-mandelic acid [C9H11NO2.C8H8O3], have been grown by the slow evaporation technique at room temperature using aqueous solution. The single crystal XRD study confirms monoclinic system for the grown crystal. The functional groups present in the grown crystal have been identified by FTIR and FT-Raman analyses. The optical absorption studies show that the crystal is transparent in the visible region with a lower cut-off wavelength of 257 nm and the optical band gap energy Eg is determined to be 4.62 eV. The Kurtz powder second harmonic generation was confirmed using Nd:YAG laser with fundamental wavelength of 1064 nm. Further, the thermal studies confirmed no weight loss up to 150˚C for the as-grown crystal. The photoluminescence spectrum exhibited three peaks (414 nm, 519 nm, 568 nm) due to the donation of protons from carboxylic acid to amino group. Laser damage threshold value was found to be 4.98 GW/cm2. The Vickers microhardness test was carried out on the grown crystals and there by Vickers hardness number (Hv), work hardening coefficient (n), yield

1

strength (σy), stiffness constant C11 were evaluated. The dielectric behavior of the crystal has been determined in the frequency range 50 Hz - 5 MHz at various temperatures. Keywords: Optical materials, Crystal growth, Raman spectroscopy, X-ray diffraction, Optical properties, Second harmonic generation. *Corresponding author: Dr. M. Lydia Caroline, Assistant Professor, PG & Research Department of physics, Arignar Anna Govt. Arts College, Cheyyar -604 407, Tamilnadu, India. Tel: +91 9841720216, Fax: +0091-04182-222286. E-mail: [email protected] 1. Introduction Nonlinear optical (NLO) materials have the influence of generating the second harmonic frequency, which plays an important role in understanding the new physical happening, but also in realizing technological applications [1]. Organic crystals exhibit second order optical nonlinearities are the key materials for their use in frequency doublers, electro-optic modulators, optical limiters, high speed optical gates and parametric amplifiers. These materials show large second order nonlinear optical properties and short transparency cut-off wavelength [2]. Production of organic crystals using crystal growth methods such as from solution process is most commonly employed. The organic nonlinear crystals show poor physico-chemical stability and low mechanical strength. The excellent nonlinear and electro-optic property is perfectly exhibited in amino acid based crystals which has great attention in photonic industry [2]. A sequence of second order NLO active materials composed of L-phenylalanine have been synthesized, such as, L-phenylalanine benzoic acid [3], L-phenylalanine L-phenylalaninium malonate [4], L-phenylalanine fumaric acid [2]. Hence this paper deals with L-phenylalanine, an α-amino acid mixed with dl-mandelic acid in 2

the stoichiometric molar (1:1) ratio. Already the diastereomeric crystallization of the title compound was studied by Xuan-Hung Pham et al [5]. Some works based on mandelic acid have been already reported in the literature [6-9]. To the best of author’s knowledge, growth and characterization studies of LPDLMA have not been studied till now. Moreover the crystal structure of the title compound was reported by Kimio OKAMURA et al [10]. In the present work, we report for the first time, spectral, thermal, microhardness, laser damage threshold, photoluminescence and second harmonic generation properties of optically clear crystals of L-phenylalanine dl-mandelic acid (LPDLMA) grown by slow evaporation technique using aqueous solution, in order to understand its suitability in nonlinear optical devices . 2. Materials and methods The starting materials L-phenylalanine and dl-mandelic acid taken in stoichiometric molar (1:1) ratio have been used to synthesize the LPDLMA. The chemical reaction scheme is given in Fig. 1. The calculated amounts of the reactants were thoroughly dissolved in aqueous solution and there after continuous stirring was done for about 6h to obtain LPDLMA precursor homogenous clear solution.

The clear solution was filtered off to

remove insoluble impurities and transferred to crystal growth vessels for slow evaporation to take place at room temperature. Optically good transparent colorless crystals having good dimensions were harvested within a span of 2 weeks. The photograph of the as-grown crystals of LPDLMA is depicted in Fig. 2.

3

Fig. 1. Reaction scheme of L- phenylalanine dl- mandelic acid.

Fig. 2. Photograph of the grown LPDLMA crystals. 2.1. Characterization studies The harvested good quality single crystals of LPDLMA were subjected to various characterization methods like single crystal X-ray diffraction, Fourier transform infrared (FTIR), FT-Raman, UV-visible, thermal analysis, NLO studies, laser damage threshold, 4

photoluminescence, microhardness and dielectric studies. The cell parameters of the grown LPDLMA crystals were found using a BRUKER KAPPA APEX II CCD, diffractometer employing M0Kα (λ=0.71073Å) radiation. A PERKIN ELMER Fourier transform infrared spectrometer was employed to determine the infrared spectrum at room temperature in the range of 4000-400 cm-1, using KBr pellet. The FT-Raman spectra of LPDLMA were recorded on a Bruker IFS-88 spectrometer in the range 4000-450 cm-1. The UV-visible transmission property of the material was investigated using a PERKIN ELMER LAMBDA 35 UV-visible spectrometer in the wavelength range 200-700 nm. The relative second harmonic generation efficiency of LPDLMA with respect to KDP was measured by Kurtz and Perry powder technique using pulsed Nd:YAG laser. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out using a SII NANO TECHNOLOGY (MODEL TG/DTA 6200) in the temperature range 50 - 500˚C at a heating rate 20˚C/min in the presence of nitrogen atmosphere. The laser damage threshold value of LPDLMA crystal was measured using 1064 nm Q-switched Nd:YAG laser system with laser input pulse duration of 6 ns at a rate of 10 Hz. Photoluminescence spectrum of LPDLMA was recorded using PERKIN ELMER LS-45 spectrofluorophotometer in the range 300-700 nm. The microhardness of the LPDLMA crystal was measured at room temperature on the Leitz Wetzler Vickers microhardness tester fitted with the Vickers pyramidal indentor. Flat and polished surfaces of LPDLMA crystal with known dimensions was subjected to dielectric measurement by employing a dielectric HP 4275 multi frequency LCR meter, for the frequencies varying from 50 Hz to 5 MHz at various temperatures

(313 K, 333 K, 353 K and 373 K).

5

3. Results and discussion 3.1. Single crystal x-ray diffraction analysis For the grown LPDLMA, single crystal X-ray diffraction studies disclosed monoclinic crystal system with acentric space group C2. The obtained lattice parameters are presented in Table 1, along with values reported in literature [10] for the sake of comparison. The calculated values are in good agreement with reported work. Table 1 Single crystal XRD data of LPDLMA. Cell parameters

Present work

Reported work [10]

Monoclinic

Monoclinic

C2

C2

a (Å)

19.72

19.83

b (Å)

5.53

5.55

c (Å)

17.44

17.09

(˚)

126.06

123.83

1537

1570

Space group

Volume (Å3)

3.2. FTIR and FT-Raman spectral analyses FTIR spectrum is important evidence which provides more information about the structure of a compound from vibrational interactions of various functional groups. The absorption of IR radiation causes the various bands in a molecule that exhibit stretch and bend with respect to one another. The FTIR and FT-Raman spectrums of LPDLMA recorded are shown in Fig. 3(a) and Fig. 3(b) respectively. The peaks observed at 3089 cm-1 and 6

3060 cm-1 in FTIR and FT-Raman are attributed to NH3+ asymmetric stretching [2]. The CH2 stretching is found to appear at 2871 cm-1 and 2905 cm-1 respectively in FTIR and FT-Raman spectra. The CH stretching vibrations gives rise to peaks at 2096 cm-1 in IR and 2076 cm-1 in Raman spectra [11]. The C=O stretching for FTIR is seen at 1607 cm-1 and for counterpart FT-Raman at 1604 cm-1 [11]. The peak at 1495 cm-1 in FTIR and one at 1451 cm-1 in FT-Raman are assigned to COO- symmetric stretching. The peaks around 1359 cm-1 and 1356 cm-1 indicate the presence of C-N stretching vibrations, respectively in FTIR and FT-Raman. The wave numbers occurring at 1328 cm-1 and 1326 cm-1 may be attributed due to OH in plane bending in FTIR and FT-Raman respectively. The sharp peaks at 1034 cm-1 in FTIR and at 1032 cm-1 in FT-Raman are assigned to C-NH2 stretching vibrations. The benzene ring deformation is due to bands at 869 cm-1 and 862 cm-1 in FTIR and FT-Raman. The intense sharp band at 745 cm-1 and 765 cm-1 establishes the presence of CH2 rocking vibration, respectively in FTIR and FT-Raman. In FTIR spectrum, the absorption bands at 588 cm-1 and 484 cm-1 are attributed to C-C stretching vibrations and in FT-Raman counterpart same absorption bands are observed at 618 cm-1 and 491 cm-1 respectively.

7

Raman intensity(a.u)

0.6 0.5 0.4

13261032

3060

(b)

2905

0.3

1604

0.2

1356

618 862

1451

2076

765

491

0.1 0.0

Transmittance (%)

100 80

745

1607

(a)

1034 1359

60 2096

40 20 0

3089

4000

1495

2871

3000

2000

-1

Wavenumber(cm )

1328

869

484 588

1000

0

Fig. 3. (a) FTIR spectrum and (b) FT-Raman Spectrum of LPDLMA.

3.3. UV-visible studies The optical absorption spectrum for the grown crystal was recorded in the range 200-700 nm using LAMBDA-35 UV-visible spectrophotometer. Covering the entire near-UV and visible region, the spectrum gives important structural information since absorption of UV and visible light involves raising of the electrons in p and n orbitals from the ground state to higher energy states [12]. As observed in the spectrum in Fig. 4(a), there is no significant absorption in the wavelength range 250-700 nm, which is an advantage of employing amino acids, due to the absence of strongly conjugated bonds thus leading to wide transparency ranges in the visible and UV spectral regions [4]. The low UV cut-off wavelength observed at 257 nm suggest the suitability of this material in generating blue violet light using a diode laser [12]. 8

100

2.5

2.0

50



1.5

(b)

75

h x10 6 (eV/m) 2

Absorbance (arb.unit)

(a)

25 Eg = 4.62 eV

1.0 0

0.5

2.0

2.5

3.0

3.5

4.0

Photon energy (eV)

4.5

5.0

0.0 200

300

400

500

600

700

Wavelength (nm) Fig. 4. (a) UV-vis spectrum and (b) Tauc’s plot of LPDLMA.

3.3.1. Band gap energy The optical absorption coefficient (α) of LPDLMA crystal at different wavelengths was calculated using Tauc’s relation [13]:



A(h  E g )

1

2

Eq. (A.1)

h

A Tauc’s plot of (αhυ)2 vs hυ (Fig. 4(b)) has been drawn to evaluate the band gap value, where α is the absorption coefficient, hυ is the photon energy (eV) and Eg is the optical energy gap. The optical band gap of the crystal was estimated by extrapolation of the linear part of the graph and the value Eg has been found to be 4.62 eV. The width of the energy gap increases as the defect concentration decreases. Thus, the larger optical band gap indicates 9

that the defect concentration in the grown LPDLMA crystal is very low [14]. The wide optical band gap suggests that the crystal could be a suitable material for the optoelectronic applications. 3.3.2. Urbach energy In the exponential-edge region, the absorption coefficient below the fundamental absorption edge for the crystalline materials show an exponential dependence on the photon energy (hυ) which is expressed by the so called Urbach relationship [15], α(hυ) = α0 exp (hυ/Eu)

Eq. (B.1)

Where α0 is a constant, Eu the Urbach energy, which is indicated as the width of the tail of localized states in the forbidden band gap, h is planck’s constant and υ is the frequency of radiation. The relation represented in Eq. (B.1) has been first proposed by Urbach to find the absorption edge in alkali halide crystals [15]. Fig. 5 shows the logarithm of the absorption coefficient (α) with photon energy (hυ). From the slope of the plot ln(α) vs hυ, the value of Urbach energy is calculated. The observed slope value is 5.0627 of the linear portion of the plot. The reciprocal of the linear portion of the plot gives the value of Urbach energy and is estimated to be 0.1975 eV. The computed low value of Urbach energy (0.1975 eV) shows a minimum structural defect in grown LPDLMA crystal, supports its good NLO performance.

10

Slope= 5.0627

0.6

2

-1

ln ( (m )

R = 0.9656 Eu = 0.197 eV

0.3

0.0

4.70

4.75

heV)

4.80

Fig. 5. Plot ln(α) vs hυ for the LPDLMA.

3.4. Powder SHG measurement Kurtz Powder technique was employed for screening the materials for second harmonic generation [16]. The fundamental beam of 1064 nm from a Q-switched Nd:YAG laser was used to test the second harmonic generation property of LPDLMA crystal. The crystalline samples were powdered and its SHG output was compared with well known SHG material such as KDP. Both the powdered samples were packed in micro-capillary tubes and exposed to laser radiation with the input beam energy of 0.69 J (1064 nm, 10 ns, 10 Hz). The SHG output (532 nm) is finally detected by a photomultiplier tube and displayed on the oscilloscope. SHG efficiency was found to be 0.35 times of KDP. Some of the reported non-centrosymmetric crystals with respective space group and SHG efficiency are given in Table 2 for comparison.

11

Table 2 A comparison SHG efficiency of non-centrosymmetric crystals. Crystal

spacegroup

SHG efficiency

Reference

Ethylenediamine ditartrate dehydrate

P21

0.13

[17]

L-phenylalanine nitric acid

P21

0.26

[3]

L-alanine

P21

0.33

[18]

L-phenylalanine dl-Mandelic acid

C2

0.35

Present work

3.5. Thermal studies The thermal behavior of LPDLMA was examined by thermogrammetric analysis (TG) and differential thermal analysis (DTA) using the LPDLMA sample of 7 mg at the beginning. A thermal analyzer was employed at a heating rate 20˚C/min in the nitrogen atmosphere. The thermogram obtained from TG and DTA analyses recorded at 20-500˚C are shown in Fig. 6. The TGA spectrum indicates that there is no weight loss up to 150˚C which confirms the absence of water of crystallization in the title compound. There after weight loss occurs in a single step between 150˚C to 475˚C which gradually decreases to zero weight. Differential thermal analysis (DTA) curve shows two endothermic peaks. It implies that the material undergoes an endothermic transition at 160˚C, which promptly indicate the first stage of decomposition of the material, coincides well with the TGA spectrum. The second endothermic peak at 204˚C may be due to the decomposition and volatilization of the compound. Based on the result of TGA and DTA, the maximum temperature for NLO application for this crystal is limited to 150˚C.

12

35 80



489.8 C

70

30

99.6%

60 25 40

20

30

TG %

DTA μV

50

15 20



204.2 C

10

10 

160.1 C

0

5 -10 -20 50

100

150

200

250

300

350

400

450

500

0 550

o

Temperature  C)

Fig. 6. TG and DTA curves of LPDLMA.

3.6. Laser damage threshold study The laser damage threshold of LPDLMA crystal was calculated by employing a Nd:YAG laser. In the present study an actively Q-switched Nd:YAG laser source with a pulse width of 6 ns and a repetition rate of 10 Hz was used. The laser damage density of LPDLMA crystal was calculated using a power meter. The surface damage threshold of the crystal was evaluated using the expression [19], Power density (Pd) = E/τπr2

Eq. (C.1)

Where E is input energy (mJ), τ is the pulse width (ns) and r is the radius of the laser beam spot (mm). A well polished plane of the grown LPDLMA crystal suitable to measure the multiple shot laser damage threshold was selected. The laser beam of diameter was 1 mm was 13

focused on the crystal. The sample was placed at the focus of a plano-convex lens of focal length 20 cm. The multiple shot laser damage threshold value is determined to be 4.98 GW/cm2 for 1064 nm wavelength of Nd:YAG laser radiation. The present sample of laser damage threshold value in comparison with other organic crystals is given in the Table 3. Table 3 Comparison of laser damage threshold values. Crystal

Laser damage

Reference

Threshold Value (GW/cm2) 0.2

KDP

[20]

Urea

1.5

[20]

Dimethyl amino pyridinium 4-nitrophenolate

2.24

[21]

Guanidinium phenyl arsonate

4.07

[22]

L-phenylalanine dl-Mandelic acid

4.98

4-nitrophenol

Present work

3.7. Photoluminescence study Photoluminescence (PL) spectroscopy is one of the nondestructive tools to understand the electronic energy band structure of material [23]. Basically, the luminescence phenomenon indicates the presence of intrinsic behavior in the forbidden band region of the LPDLMA crystal. PL was carried out by PERKIN ELMER LS 45 spectrofluorophotometer and excitation source used was Xenon arc lamp (150W). A broad PL spectrum obtained from LPDLMA in the wavelength range of emission spectrum 300-700 nm (4.14-1.77 eV) is 14

shown in Fig. 7. The excitation wavelength 257 nm chosen from UV-visible study is identified from the value of optical band gap. The result shows that LPDLMA crystal has one peak of violet emission at 414 nm (2.99 eV). The obtained two peaks corresponding to appeared green emission one with high PL intensity at 519 nm (2.39 eV), and other with weak shoulder corresponding to the decreased PL intensity at 568 nm (2.18 eV). The photoluminescence emission occurs due to donation of proton from carboxylic acid to amino group in grown crystal. Fig. 8 shows the energy levels based on the obtained excitation wavelength and emission spectrum. The materials with photoluminescence of violet and green emissions are found to be more useful for OLED applications [24].

400

519

350

Intensity (arb.u)

300 250 200 150

568

414

100 50 0 300

400

500

600

Wavelength (nm)

Fig. 7. Emission spectrum of LPDLMA.

15

700

Fig. 8. Energy level spectrum of LPDLMA.

3.8. Microhardness study Microhardness testing is extremely an important property of device fabrication to explore the mechanical strength of solids. The hardness of material depends on various parameters such as lattice energy, Debye temperature, heat of formation and interatomic spacing. The Vickers microhardness measurement emphasizes the mechanical property of as-grown LPDLMA crystal. The hardness measurement was carried out at room temperature and loads of various magnitudes such as 25, 50 and 100 g were applied. For a specified load at least five well-defined impressions were considered and the mean of the all the diagonals (d) were calculated. Function of the applied load and the diagonal of the indent are expressed as hardness. The Vickers hardness was measured using the standard formula Hv = 1.855 (P/d2)

Eq. (D.1)

16

where P is the applied load in kg, d is the mean length of the indenter impression in mm, and 1.8544 is a constant of geometrical factor for the diamond pyramid indenter. Fig. 9(a) shows the variation of hardness number (Hv) as a function of applied load ranging from 25-100 g for LPDLMA crystal. It is noted from the figure that Hv increases with an increase in the load emphasizes reverse indentation size effect [RISE] [25-27]. The Meyer’s index coefficient was calculated from the Meyer’s law [28], which relates the load and indentation diagonal length, P = K1dn

Eq. (D.2)

(or) log P = log K1 + n log d

Eq. (D.3)

where K1 is the material constant and ‘n’ is the Meyer’s index (or) work hardening exponent. That characterizes the materials category. In order to calculate the value of work hardening coefficient ‘n’, a graph is plotted between log P vs log d and is shown in Fig. 9 (b). The slope of the linear fitted straight line gives the value of ‘n’ and is found to be 3.85. For the normal ISE behavior, we have n < 2. When n > 2, there is a reverse ISE behavior. This is good agreement with the experimental data and thus confirms the reverse ISE. According to Onitsch [29], work hardening coefficient ‘n’ evaluated should lie between 1 and 1.6 for harder materials and above 1.6 for softer materials. Hence, LPDLMA is categorized under soft material category. From the hardness value the yield strength (σy) also has been obtained using the relation (for n > 2) [30],

y 

Hv (0.1) n2 3

Eq. (D.4)

Where n′ = n+2. The elastic stiffness constant (C11) was calculated using Wooster’s empirical relation [31]: 17

C11 = Hv7/4

Eq. (D.5)

The calculated stiffness constant C11, yield strength σy and Vickers hardness values for different loads from 25-100 g are compiled in Table 4. Table 4 Calculated mechanical parameters of LPDLMA. Hv (kg mm-2)

n

σy (GPa)

C11 (GPa)

25

41.3

3.85

37.91

6.72

50

69.5

3.85

63.80

16.72

100

80.65

3.85

74.04

21.68

Load P (g)

80

(a)

2.0

(b) 60

1.8

Log P (kg)

2 Hv (kg/mm )

70

1.6

50

1.4

40

1.50

1.55

1.60

1.65

1.70

Log d (m)

20

40

60

80

100

120

Load P (kg) Fig. 9 (a) Variation of (Hv) with load P and (b) Plot of log P with log d for LPDLMA. 18

3.9. Dielectric studies Dielectric measurement is one of the useful ways to exhibit the characterization of electrical response of the solids [32]. Dielectric properties can be correlated with electro-optic property of the crystal [33]. The dielectric study of LPDLMA was carried out for the frequencies range 50 Hz - 5 MHz for various temperatures 313 K, 333 K, 353 K, and 373 K respectively. The real part of the dielectric constant (εʹ) and imaginary part of the dielectric constant (εʹʹ) of the crystal have been evaluated using the relations

 

Cd A 0

Eq. (E.1)

and εʹʹ = εʹ tan δ

Eq. (E.2)

respectively. Where C is the capacitance, d the thickness of the sample, A the area of the sample and ε0 the permittivity of free space, where tan δ is the dissipation factor. The variation of dielectric constant (εʹ) and dielectric loss (εʹʹ) against logarithm of frequency at various temperatures are shown in Fig. 10(a) and Fig. 10(b). From the graphs it is clear that the values of dielectric constant and dielectric loss decreases with increase in frequency. The dielectric loss strongly reliant on the frequency of the applied field. The large values of (εʹ) at low frequencies may be due to the contribution from electronic, ionic, orientional and space charge polarization and its low value of (εʹ) at high frequency may be due to the loss of magnitude of these polarizations gradually [34]. The indicative of low dielectric loss and dielectric constant at higher frequencies clearly reveals defect less optical quality of the crystals which focus to a desirable property for nonlinear optical crystals [35, 36].

19

400

(a)

30

313 K 333 K 353 K 373 K

(b)

25

Dielectric loss ('')

Dielectric constant (')

300

200

20 15 10 5 0 1

100

2

3

4

Log f (Hz)

5

6

7

0 1

2

3

4

Log f (Hz)

5

6

7

Fig. 10. (a) Plot of log frequency vs dielectric constant and (b) Plot of log frequency vs dielectric loss of LPDLMA. 4. Conclusions Single crystals of LPDLMA, was synthesized and grown from aqueous solution by slow evaporation solution growth technique in a period of about 2 weeks. The single crystal structure determination established the lattice parameters of the grown crystal. The chemical constitutions of the crystals have been confirmed by identification of the functional groups by FTIR and FT-Raman analyses. From UV-visible spectrum, cut-off wavelength and optical energy band gap found to be 257 nm and 4.62 eV are supportive parameters in regard of NLO applications. Second harmonic generation (SHG) efficiency of LPDLMA is evaluated as 0.35 times that of KDP. The TGA and DTA analyses confirmed that the material is stable up to 150˚C. The surface laser damage threshold value was estimated to be 4.98 GW/cm2. Photoluminescence spectral study revealed the electron excitation in the grown LPDLMA crystal. The various mechanical parameters deduced from Vickers microhardness study 20

contribute the hardness nature of the as-grown crystal. The dielectric studies proves that the crystal exhibit low dielectric constant and dielectric loss at high frequency region. From the above criterions, LPDLMA crystal proves it to be a versatile candidate for the fabrication of photonic devices. Acknowledgements One of the authors P. Jayaprakash expresses his sincere thanks for the scientific supports extended by sophisticated analytical instruments facility (SAIF), Indian Institute of Technology (IITM) for support in single crystal XRD measurement. Also the facilities rendered by Department of Physics, and Department of Polymer and Nanoscience of BS Abdur Rahman university (BSAU), Chennai for providing SHG facility and thermal analysis measurement are gratefully acknowledged. One of the authors (P.J) expresses his sincere thanks to St.Joseph’s College Trichy and Loyola College, Chennai for providing the microhardness and dielectric facilities. References [1] P.N. Prasad, D.J. Williams, Introduction to Nonlinear Optical Effect in Molecules and Polymers, John Wiley & Sons, New York, 1991. [2] M. Prakash, D. Geetha, M. Lydia Caroline, Growth and characterization of Nonlinear Optics (NLO) active L-phenylalanine fumaric acid (LPFA) single crystal, Materials and Manufacturing processes, Taylor & Francis 27 (2012) 519-522. [3] M. Lydia Caroline, S. Vasudevan, Growth and characterization of L-phenylalanine nitric acid, a new organic nonlinear optical material, Mater. Lett . 63 (2009) 41-44. [4] M. Prakash, D. Geetha, M. Lydia Caroline, P.S. Ramesh, Crystal growth, structural, optical, dielectric and thermal studies of an amino acid based organic NLO material: L21

Phenylalanine L-Phenylalaninium malonate, Spectrochimica Acta Part A 83 (2011) 461466. [5] Xuan-Hung Pham, Jong-Min Kim, Sang-Mok Chang, In-ho Kim, Woo-Sik Kim, Enantioseparation of D/L-mandelic acid with L-phenylalanine in diastereomeric crystallization, J. Molecular Catalysis B Enzymatic, 60 (2009) 87-92. [6] Hui-Shi Guo, Jong-Min Kim, Sang-Mok Chang, Woo-Sik Kim, Chiral recognition of mandelic acid by L-phenylalanine-modified sensor using quartz crystal microbalance, Biosensors and Bioelectronics 24 (2009) 2931-2934. [7] M. Babji, A. Mondry, Synthesis, structure and spectroscopic studies of europium complex with S (+) mandelic acid, J. Rare Earths 29 (2011) 1188-1191. [8] M. Badawi, Wolfgang Forner, Analysis of the infrared and Raman Spectra of Phenylacetic acid and mandelic (2-hydroxy-2-phenylacetic) acid, Spectrochimica Acta Part A 78 (2011) 11621167. [9] Michal Babji, Przemyslaw Starynowicz, Anna Mondry, Structural and spectroscopic studies of neodymium complexes with S (+)-mandelic acid, J. Molecular structure. 1006, 2011, 672-677. [10]

Kimio

NISHIMURA,

OKAMURA, Tadashi

Kei-ichi

SATO,

AOE,

Keiji

Hhajime

HASHIMOTO,

HIRAMATSU, Crystal

Noriyuki

Structures

of

Diastereomeric 1:1 Complexes of (R) - and (S) - Phenylalanine (S) - Mandelic Acid, Analytical Sciences 13 (1997). [11] George Socrates, Infrared and Raman Characteristic Group Frequencies, John Wiley & Sons Publishers, 3rd ed., England, 2001.

22

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Table captions Table 1 Single crystal data of LPDLMA. Table 2 A comparison SHG efficiency of non-centrosymmetric crystals. Table 3 Comparison of laser damage threshold values. Table 4 Calculated mechanical parameters of LPDLMA. Figure caption Fig. 1. Reaction scheme of L- phenylalanine dl- mandelic acid. Fig. 2. Photograph of the grown LPDLMA crystals. Fig. 3. (a) FTIR spectrum and (b) FT-Raman Spectrum of LPDLMA. Fig. 4. (a) UV-vis spectrum and (b) Tauc’s plot of LPDLMA. Fig. 5. Plot ln(α) vs hυ for the LPDLMA. Fig. 6. TG and DTA curves of LPDLMA. Fig. 7. Emission spectrum of LPDLMA. Fig. 8. Energy level spectrum of LPDLMA. Fig. 9. (a) Variation of (Hv) with load P and (b) Plot of log P with log d for LPDLMA. Fig. 10. (a) Plot of log frequency vs dielectric constant and (b) Plot of log frequency vs dielectric loss of LPDLMA.

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