Accepted Manuscript Crystal Growth, Spectral, Optical, Laser damage, Photoconductivity and Dielectric Properties of Semiorganic L-cystine hydrochloride Single Crystal SenthilKumar Chandran, Rajesh Paulraj, P. Ramasamy PII: DOI: Reference:

S1386-1425(15)30034-2 http://dx.doi.org/10.1016/j.saa.2015.06.113 SAA 13883

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

15 December 2014 24 June 2015 25 June 2015

Please cite this article as: S. Chandran, R. Paulraj, P. Ramasamy, Crystal Growth, Spectral, Optical, Laser damage, Photoconductivity and Dielectric Properties of Semiorganic L-cystine hydrochloride Single Crystal, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.06.113

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Crystal Growth, Spectral, Optical, Laser damage, Photoconductivity and Dielectric Properties of Semiorganic L-cystine hydrochloride Single Crystal SenthilKumar Chandran, Rajesh Paulraj*, P.Ramasamy Centre for crystal growth, Department of Physics, SSN College of Engineering, Kalavakkam, Tamilnadu, India-603 110 ABSTRACT The semiorganic single crystals of L-cystine hydrochloride have been grown by slow evaporation solution growth technique at 40 °C. The grown crystals were subjected to single

crystal

XRD,

FTIR,

optical

absorbance,

laser

damage

threshold,

photoluminescence, photoconductivity and dielectric studies. Single crystal XRD studies reveal that the crystal belongs to monoclinic system with space group C2 and the lattice parameters are a = 18.63 (Å), b=5.28 (Å), c=7.26 (Å), α=90°, β=103.70°, γ =90° and V=696(Å3). FTIR spectroscopy confirms that a band at 1731 cm-1 represents characteristic of α-amino acid hydrochlorides. The UV–Vis-NIR absorption spectrum was analyzed and the optical band gap energy was found to be 3.8 eV. The crystal exhibits sharp emission peak at 388 nm. The thermal characteristics of crystals were studied by TG-DTA, which indicate that there is no weight loss upto 201 °C. Surface laser damage threshold value of title compound was estimated using high power Qswitched Nd:YAG laser operating at 1064 nm. Dielectric and photoconductivity studies were also carried out for the grown crystals. Keywords: Crystal Growth; Dielectric properties; Photoconductivity; Laser damage threshold; Single crystal X-ray diffraction. *Corresponding author: Tel: +91 9445434893: Email: [email protected] 1

1. Introduction In last two decades, extensive studies have been made for obtaining new nonlinear optical (NLO) materials because of their potential applications in the field of optical modulators, telecommunications, color displays, optical switching and optical signal processing [1-3]. Inorganic materials have high melting point, high mechanical strength, high degree of chemical inertness and low optical nonlinearity. Organic materials have excellent properties compared to the inorganic solids which show lower dielectric constants and enhanced NLO responses. Organic non-linear optical crystals are usually formed by weak Vander-Waals and hydrogen bonds. So they possess poor mechanical and thermal properties. [2-4]. In order to overcome the limitations of those materials, in recent years the organic materials were mixed with inorganic material (semi-organic) to improve their chemical stability, physicochemical properties, mechanical strength, laser damage threshold, optical nonlinearity and thermal stability [5-7] . In this point of view, some complexes of amino acid have been combined with inorganic compounds such as dichloro (4-hydroxy-lproline) cadmium(II) [2], L-proline cadmium chloride monohydrate[3], L-alanine Sodium Nitrate[5], glycine sodium nitrite[6], L-arginine hydrochlorobromide [7], Lcystine dihydrochloride [8] and L-cystine dihydrobromide [9]. In this series, Lcystine hydrochloride is also a good and promising candidate for SHG and various other applications in the semi-organic family. Amino acids are bifunctional organic molecules that contain both a proton donor carboxylic (COO-) and proton acceptor amino group (NH2). This dipolar nature of amino acids shows peculiar physical and chemical properties. L-cystine is a sulphur-containing amino acid. In the L-cystine 2

molecule, the functional groups, such as NH2 and COOH have a strong tendency to coordinate with inorganic cations and metals [8-10]. The molecular structure of Lcystine hydrochloride was reported by Srinivasan et al [10] and the NLO and mechanical stability were studied by Selvaraju et al [11]. Single crystals play vital role in laser technology, optoelectronics, microelectronics industry and so on. From application point of view, its needs wide optical transparency, high mechanical strength, large laser damage threshold, high thermal behavior and low dielectric properties [5, 6, 12-15]. Based on the above aspects, the present paper describes and discusses

the

optical,

laser

damage

threshold,

photoconductivity,

photoluminescence, TG/DTA and dielectric properties of semi-organic L-cystine hydrochloride crystal. 2. Experimental technique 2.1 Material synthesis and crystal growth L-cystine hydrochloride crystal is synthesized using L-cystine and hydrochloric acid ( Merck GR ) which are mixed in the stoichiometric ratio of 1:1 in deionised water which has resistivity of 18.2 MΩ cm. The calculated amount of L-cystine was first dissolved in the deionised water. The solution was thoroughly stirred for 4 h using magnetic stirrer at 40 °C. The mixture of solution was found to be cloudy and HCl was added and stirred well for 24 h till a clear solution was obtained. Then the saturated solution was filtered using Whatman filter paper in clean vessels and the vessels containing the solution were closed with polythene covers and domiciliated in the constant temperature bath at 40 °C. The synthesized salt was sanctified by consecutive recrystallization activity. Optically

3

transparent single crystals were obtained after 35 days and the harvested crystals are shown in Fig. 1. 2.2. Characterization techniques Single crystal X-ray diffraction analysis was carried out using a Bruker AXS Kappa APEX II CCD Diffractometer, equipped with graphite-monochromated MoKα radiation (λ=0.71073Å) to identify the crystal structure and to estimate the lattice parameter values. FTIR spectrum of the title compound was recorded using Bruker AXS FTIR spectrometer in the range of 500–4000 cm-1 with single reflection ATR accessory. The UV–Vis-NIR spectrum for the L-cystine hydrochloride crystal was recorded using Perkin Elmer Lambda 35 spectrometer at room temperature in the range 200–1100 nm. The LDT study for the grown crystal was carried out using the high-power Q-switched Nd:YAG laser with 10 Hz pulse repetition rate. The pulse width of the laser is 7 ns for 1064 nm. A highly polished clear surface and defect free crystal with the thickness of 1.5 mm is used for the LDT measurement. The dielectric behavior of L-cystine hydrochloride crystal was carried out using Agilent Model 4284A LCR meter in the frequency range 1 KHz to 1 MHz at various temperatures (40 °C-100 °C). Silver paste was coated on both sides of the L-cystine hydrochloride crystal and then placed between the two copper electrodes to form the parallel plate capacitor. The photoconductivity studies were carried out on a cut and polished sample of the grown single crystal by using KEITHLEY 6487 picoammeter in the presence of DC electric field at room temperature (303 K). Silver paint was coated on the surface of the crystal in order to make contact between the electrode and the crystal. The sample is kept in vacuum. 4

The light from a halogen lamp of 100 W was used to measure the photocurrent (Ip). The weight loss (TG) and energy change analyses (DTA) of L-cystine hydrochloride samples were carried out in the temperature range between 35 °C and 300 °C at a heating rate of 10 °C/min under nitrogen atmosphere using Perkin Elmer Diamond TG-DTA instrument. A small piece of crystal weighing 4.432 mg was taken for the measurement. The photoluminescence measurements have been carried out using Shimadzu Spectrofluorophotometer R.F-5031 PC series with the slit width of 3 nm at room temperature. 3. Results and discussion 3.1 Single crystal X-ray diffraction From single crystal X-ray diffraction analysis, it was confirmed that the crystal belongs to monoclinic system with space group C2. Lattice parameters are a = 18.63 (Å), b=5.28 (Å), c=7.26 (Å), α=90°, β=103.70°, γ=90° and the volume of the unit cells is found to be V=696(Å3), which is in close agreement with the reported values [10]. The lattice parameters are given in table 1. 3.2 FTIR spectral analysis The FTIR spectrum of L-cystine hydrochloride is shown in Fig.2. The band at 2893 cm-1 is assigned to the CH2-S asymmetric stretching mode of vibration. The absorption peak at 2630 cm-1 is due to NH+3 symmetric stretching mode of vibration. The intense absorption bands at 1572 cm-1 and 823 cm-1 are due to the asymmetric deformation and rocking vibrations of NH+3. The peak observed at 1496 cm-1 has been assigned to stretching vibration of COO−.

The sharp peak at 1428 cm-1 can be assigned to the CH2-CO

deformation. The stretching vibrations of C-C occur at 1377 cm-1, 1184 cm-1 and 1128 5

cm-1. Band at 1226 cm-1 is due to CH2 wagging, C–S stretching vibration at 664 cm-1 confirmed the presence of S–S group. A band at 1731 cm-1 represents characteristic of α-amino acid hydrochlorides. The peak appearing at 1043 cm-1 is owing to C-N stretching vibration. Thus FTIR analyses confirm the presence of the functional groups of L-cystine hydrochloride and the vibrational frequencies compare with the corresponding reported values [8,11, 16 ]. 3.3 Optical absorption studies Optical transmission and absorption are important factors to identify NLO material. Crystals to be used for optical applications must have wide transparency with little absorption [17]. The UV-Vis-NIR absorption spectrum is shown in Fig.3. The cutoff wavelength of grown crystal occurs at ~360 nm. The grown crystal has a characteristic absorption in ultraviolet region (UV) this may be due to electronic transitions occurring in the carboxylate (COO-) and nitryl (NH3+) bonds and there is no significant absorption band between 360 and 1100 nm (Visible and near IR). The similar behavior has been observed for L-threonine [18]. The optical absorption co-efficient (α) was calculated using the formula,

α=

2.306 A d

(1)

where, A is the absorption and d is the thickness of the sample. The direct optical band gap energy was evaluated using the following expression, 1

αhυ = A(hυ − E g ) 2

(2)

where, h is Planck's constant, A is the constant, E g is the optical band gap energy and υ is the frequency of incident light. The optical band gap energy of the grown 6

2

crystal was estimated by plotting (αhυ ) versus (hυ ) shown in Fig.4. The estimated value of optical band gap

energy was 3.8 eV. The study of optical absorption

coefficient with the photon energy helps to understand the type of transition of the electron and the band structure. As a consequence of wide band gap, L-cystine hydrochloride crystal can be a suitable material for the optoelectronics and NLO applications [17-20]. 3.4 Laser damage threshold (LDT)

One of the most important considerations for the photonic applications is that the NLO crystal should withstand high power laser energy [21-22]. The LDT value in the crystals is induced by several physical processes such as electron avalanche, multiphoton absorption and photoionization [22-23]. It also depends on large number of laser parameters such as energy, pulse duration, properties of material, pulse width, wavelength and so on [21-24]. The laser beam was passed along the plane surface of the prepared sample. Initially 10 mJ was applied on the L-cystine hydrochloride sample and further it is increased to 20 mJ in steps of 2 mJ. There was no spot observed on the sample for 20 s. For 30 mJ, the small spot appeared after 20 s. Finally a crack was seen when applying 45 mJ for 20 s. The experiment was repeated for the different pieces of the same crystal and the same result was obtained. The energy density was calculated using the following formula, Pd =

E τπA

(7 )

7

where E is the energy (mJ), τ is the pulse width (ns) and A is the area of the spot (4.153×10-4 cm2). The calculated laser damage threshold for the grown crystal is 10.1 Gw cm-2 [17]. 3.5 Dielectric Measurements

The study of dielectric behaviour is one of the basic electrical properties of solids. The dielectric property of ionic crystals in the low frequency region depends on the crystal structure, electronic and atomic polarizability of constituent ions [20]. The dielectric constant (ε r ) of the crystal was calculated using the following relation,

εr =

Cd ε
A

(8)

where C is the capacitance, d is the thickness of the crystal, A is the area of the crystal, and ε
is the vacuum’s dielectric constant. The dielectric loss of the crystal was calculated using the relation, ε " = ε r D , where D is the dissipation factor. The variation of dielectric constant and dielectric loss of the grown crystal as a function of temperature is shown in Fig.5a and Fig.5b. The dielectric constant and dielectric loss decrease with increasing frequency and attains a constant value in the higher frequency region [24]. The low dielectric loss at high frequency of the grown crystal shows that this crystal possesses good optical quality and this parameter is of vital importance for numerous NLO materials and their applications [20, 25]. 3.6 Photoconductivity studies

The photoconductivity is an important property of solids. It gives useful information about physical properties of materials and offer applications in photodetection and radiation measurements [26]. Photoconduction takes place by any one of the following 8

mechanisms: Band-to-band transitions, Impurity levels to band edge transitions, Deep level to conduction band transitions and Ionization of donors [19]. Fig.6. shows the varation between both dark current (Id) and photo current (IP), which linearly increase with the applied electric field. The photo current is always greater than the dark current, thus confirming that L-cystine hydrochloride single crystal exhibits positive photo conductivity. Generally, positive conductivity may be attributed to generation of mobile charge carriers by the absorption of photons [19, 27]. 3.7 Thermal studies

The TG-DTA curve of grown crystal is shown in Fig.7. L-cystine hydrochloride exhibits gradual weight loss starting at 201° C, below this temperature no weight loss is seen in the TGA curve. In DTA curve, two endothermic peaks were observed at

232° C and

270° C. The thermal analysis further reveals that the thermal decomposition of L-cystine hydrochloride is comparable with well known semi organic L-cystine dihydrochloride single crystal [8]. 3.8 Photoluminescence studies

Defect free single crystal is essential from application point of view. Photoluminescence measurement is a sensitive tool to identify point defects in crystals [28]. In the present study, the sample was excited at 359 nm. The emission spectrum was recorded in the range between 370–450 nm. The excitation and emission spectra have been shown in Fig.8 (a) and Fig. 8 (b). The sharp emission peak observed at 388 nm may be due to the proton donor carboxyl acid group and the proton acceptor amino group and the results show that L-cystine hydrochloride crystal has violet fluorescence emission. From Fig.8b. the sharp intense peak indicates that the grown crystal has good crystallinity. 9

4. Conclusion

Optically good quality crystals of L-cystine hydrochloride were grown by slow evaporation solution growth technique. The UV-Vis –NIR studies show that crystal has no significant absorption in the visible and near IR region of spectrum. The laser damage threshold power density for the grown crystal is 10.1 Gw cm-2. From the dielectric measurements it is observed that the dielectric constant and dielectric loss decrease with increasing frequency. The photoconductivity studies show that L-cystine hydrochloride has positive photocurrent. It is seen from thermal analysis that the grown crystal exhibits two endothermic peaks at 232 °C and 270 °C. Photoluminescence spectrum reveals the title compound has a violet emission. Acknowledgements

The authors would like to thank Mr.Dennison, Physics Research Center, S.T.Hindu College, Nagercoil for providing the dielectric measurements.

10

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[11] K. Selvaraju, R. Valluvan, K. Kirubavathi, S. Kumararaman, Opt.Commun. 269 (2007) 230 [12] F. Helen, G. Kanchana, Mater. Chem. Phys., 151( 2015) 5. [13] P. Kumaresan, S. Moorthy Babu, P.M. Anbarasan, Opt. Mater., 30 (2008) 1361. [14] S. Goma, C.M. Padma, C.K. Mahadevan, Mater.Lett., 60 (2006) 3701. [15] K. Sugandhi, Sunil Verma, M. Jose, V. Joseph, S. Jerome Das, Optics.Laser Technology 54 (2013) 347. [16] E.Ramachandran, S. Natarajan, Cryst. Res.Technol. 39 (2004) 308. [17] Anuj Krishna, N. Vijayan, Shashikant Gupta,cKanika Thukral, V. Jayaramakrishnan, Budhendra Singh, J. Philip,f Subhasis Das, K. K. Maurya G. Bhagavannarayana, RSC Adv., 4 (2014) 56188. [18] J.J. Rodrigues Jr , L. Misoguti, F.D. Nunes, C.R. Mendonc , S.C. Zilio, Opt. Mater., 22 (2003) 235. [19] I.P.Bincy, R.Gopalakrishnan, J.Cryst. Growth 402 (2014) 22. [20] R. Surekha,R. Gunaseelan,P. Sagayaraj, K. Ambujam CrystEngComm 16 (2014) 7979. [21] Neelam Rani, N.Vijyan, B.Riscob, Suraj Karan Jat, Anju Krishna, Subhasis Das,G.Bhagavannarayana, Brijesh Rathi, M.A.Wahab, Cryst.Eng.Comm 15 (2013) 2127.

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[22] A.Senthil, P.Ramasamy J.Cryst.Growth 401 (2014) 200. [23] K. Boopathi, P. Ramasamy, G. Bhagavannarayana, J.Cryst.Growth 386 (2014) 32. [24] A.Arun Kumar, P.Ramasamy J.Cryst.Growth 401 (2014) 195. [25] R.Uthrakumar, C.Vesta, G.Bhagavannarayana, R.Robert, S.Jerome Das, J.Alloys compounds 509 (2011) 2343. [26] M. Ambrose Rajkumar, S. Stanly John Xavier, S. Anbarasu, Prem Anand Devarajan, Res. J. Physical Sci. 2 (2014) 1 [27] G.Prabagaran, S.Arulmozhi, M.Dinesh Raja, J.Madhavan, ISOR JAP 2 (2013) 51 [28] Preeti Singh, Mohd. Hasmuddin, Mohd. Shakir, N.Vijayan, M.M. Abdullah, V. Ganesh, M.A. Wahab Mater.Chem.Phys 142 (2013) 154.

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Figure Captions

Fig. 1. L-cystine hydrochloride single crystals. Fig. 2.FTIR spectrum of L-cystine hydrochloride single crystal. Fig. 3.UV-Vis-NIR absorption spectrum of L-cystine hydrochloride single crystal. Fig. 4.Band gap spectrum of L-cystine hydrochloride single crystal. Fig. 5. (a).Dielectric constant plot of L-cystine hydrochloride single crystal. (b). Dielectric loss plot of L-cystine hydrochloride single crystal. Fig.6.Photoconductivity spectrum of L-cystine hydrochloride single crystal. Fig.7.TG-DTA of L-cystine hydrochloride single crystal. Fig.8. Photoluminescence spectra of L-cystine hydrochloride single crystal. (a) Excitation spectrum and (b) emission spectrum

14

Fig.1. L-cystine hydrochloride single crystals.

15

100

664

Transmittance (%)

99

2630 1043

98

2893 1496

97

1731 96

823 4000

3500

3000

2500

2000

1500

1000

-1

Wavenumber (cm )

Fig.2. FTIR spectrum of L-cystine hydrochloride single crystal.

16

500

4.5

4.0

Intensity(a.u)

3.5

3.0

2.5

2.0

1.5

1.0 200

300

400

500

600

700

800

900

1000

1100

Wavelength(nm)

Fig.3.UV-Vis-NIR absorption spectrum of L-cystine hydrochloride single crystal.

17

7

1.2x10

7

1.0x10

6

(αhυ)

2

8.0x10

6

6.0x10

6

4.0x10

6

2.0x10

0.0 1.0

1.5

2.0

2.5

3.0

3.5

4.0

hυ(eV)

Fig.4.Band gap spectrum of L-cystine hydrochloride single crystal.

18

4.5

0.30

1 kHz 10 kHz 100 kHz 100 MHz

Dielectric loss

0.25

0.20

0.15

0.10

0.05

40

50

60

70

80

90

100

Temperature (°C)

Fig. 5(b) Dielectric loss plot of L-cystine hydrochloride single crystal.

19

Current (A)

8.0x10

-9

6.0x10

-9

4.0x10

-9

2.0x10

-9

Dark current Photo current

0.0

0

10

20

30

40

50

Applied voltage(V)

Fig.6. Photoconductivity spectrum of L-cystine hydrochloride single crystal.

20

10

201°C

100

TGA DTA

8

6

60

4

2

40

0 20

232°C

270°C -2

0

50

100

150

200

250

300

Temperature (°C)

Fig.7. TG-DTA of L-cystine hydrochloride single crystal.

21

350

Heat flow (mW)

Weight loss (%)

80

400

a 350

Intensity (counts)

300 250 200 150 100 50 0 335

340

345

350

355

Wavelength (nm)

22

360

365

400

b

Intensity (counts)

350

300

250

200

150

370

380

390

400

410

420

430

440

450

460

Wavelength (nm)

Figure 1

Fig.8. Photoluminescence of L-cystine hydrochloride single crystal (a) Excitation (b) Emission

23

Table 1 Unit cell parameters of L-cystine hydrochloride single crystal.

Lattice

Present work

R.Srinivasan et.al

Selvaraju et.al [11]

[10]

parameters a (Å)

18.63

18.63

18.68

b(Å)

5.28

5.26

5.21

c(Å)

7.26

7.28

7.21

α= γ(°)

90

90

90

β(°)

103.70

103.70

101.7

Crystal system

Monoclinic

Monoclinic

Monoclinic

Space group

C2

C2

C2

24

25

Highlights •

L-cystine hydrochloride single crystal is grown by slow evaporation technique at 40°C.

•

Optical band gap of the crystal is found to be 3.8 eV.

•

Thermally it is stable up to 201° C.

•

It exhibits violet fluorescence emission peak at 388 nm.

26