Synthesis and investigation on growth and physiochemical properties of semi organic nonlinear optical crystal l glutamic acid zinc chloride

Synthesis and Investigation on growth and physiochemical properties of semi organic nonlinear optical crystal L Glutamic Acid Zinc Chloride Accepted Manuscript Title Synthesis and Investigation on gro[.]

Title: Synthesis and Investigation on growth and

physiochemical properties of semi-organic nonlinear optical

crystal: L-Glutamic Acid Zinc Chloride

Authors: S Chennakrishnan, S.M Ravikumar, C Shanthi, R

Srineevasan, T Kubendiran, D Sivavishnu, M Packiyaraj

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Synthesis and Investigation on growth and physiochemical properties of semi-organic nonlinear optical crystal: L-Glutamic Acid Zinc Chloride

S Chennakrishnan 1 , S.M Ravikumar 2* , C Shanthi 2 , R.Srineevasan 2 ,

T Kubendiran 2 , D Sivavishnu 2 , and M.Packiyaraj 3

and the calculated lattice parameters are a = 5.20 Å, b = 6.99 Å, c = 17.58 Å, α = β = γ = 90° and Volume = 623.411Å3 Spectroscopic properties were used to investigate by recording the Fourier transform infrared and optical transmission spectra The thermal decomposition of grown crystal was investigated by Thermo Gravimetric and Differential Thermal Analysis (TG/DTA) LGAZC crystal exhibits second harmonic generation (SHG) efficiency 1.5 times than that of inorganic KDP crystal The presence of the metal ion (Zn+) in a grown crystal was identified by EDAX spectrum analysis The photoconductivity study shows that LGAZC crystal has positive Photo conducting nature The dielectric response of the LGAZC crystal was investigated and reported

Keywords

Semi-organic nonlinear optical crystal; X-ray Diffraction; UV-vis-NIR; Thermal study

1 Introduction

A new class of materials called semi-organic crystals has been investigated recently with interesting nonlinear optical properties and their stable physiochemical properties gains importance in device fabrication and applied research [1, 2] The main advantage as a increasing demand for new type of crystals in technological applications, bulk size growth of semi-organic crystals in all the three dimensions, made the growth process easy to cut and polish the samples for device fabrication [3] Possession of high nonlinearity, high resistance

to laser inducing damage, low angular sensitivity and good mechanical hardness of organic crystals property has been used potentially for combining high NLO property and chemical flexibility of organic materials with physical sturdiness and excellent transmittance

semi-of inorganic materials [4-7] Hence, ability semi-of enhancing NLO property semi-of semi-organic crystals is presently under deep investigation due to their incorporated advantages of both organic and inorganic crystals Many researchers pay their intense attention for finding the semi-organic family crystals using amino acid with inorganic or metal complexes for improving their quality and properties [8] Interestingly, amino acid based complexes have been attracted crystal researchers because of their suitability in mixing various inorganics and their crystallizing nature in crystal system favorable for nonlinear optical applications In addition, high NLO efficiency organic molecules combining approach with the favourable physical property of the inorganic materials has an active research in the last two decades

Amino acids based on several semi-organic series crystals are crystallized recently and their various properties have been analysed [9-12] High nonlinear optical coefficients organic material combines with inorganic which exhibits excellent physical properties, gives semi-organic In this device grade, semi-organic as an acid base interaction, hydrogen bonding between organic cation and inorganic anion, gives strong mechanical and high thermal stability NLO crystals [13] High polarizable, acid base interaction of organic and inorganic molecules are responsible for NLO properties, linked through hydrogen bond network yields non-cetrosymmetric structural systems reported by Srineevasan et al (2013) [14] and Rajasekaran et al (2000) [15] Rich demand of semi-organic complexes in optical storage devices, colour display and optical communication system are available in literature [16] In semi-organic complexion, π electrons movement between donor and acceptor groups has also been reported [17] A series of semi-organic compounds such as L-Arginine phosphate [18], L-Arginine hydro bromide [19], L-Arginine hydrochloride [20], L-Histidine

di hydrogen phosphate [21], L-Histidine tetra fluoroborate [22], Glycine hydrofluoride [23] and L-Glutamic hydrochloride [24] were showing good nonlinear optical property

Due to excellent physiochemical properties of amino acid family crystals they are subjected to extensive investigation by many research scientists Particularly in the view of NLO applications organic amino acids crystals are interesting because they contain donor carboxylic (COOH) group and the proton acceptor (NH2) group known as zwitterions which creates hydrogen bonds This kind of dipolar nature of amino acids proved as an ideal candidate for NLO applications The literature reveals that the complex of amino acids with inorganic (metal) salts are promising NLO materials for optical applications, such as optical communication, optical computing, optical informatics processing, optical disk data storage, laser fusion reaction and laser remote sensing [25-27] Also the considerable effort is being made to find new materials that have the optimal characteristics needed for use as a nonlinear optical element [28-32]

In recent years, tremendous efforts are given to the amino acids mixed with organic inorganic complex crystals, in order to improve the molecular engineering, chemical stability, laser damage threshold and optical properties (linear and nonlinear) Incorporating the L-Glutamic acid in many semi-organic nonlinear optical materials have been recently crystallized and their structural, optical, thermal and electrical properties have been investigated [33-38] L-Glutamic acid is a phase matchable NLO material that has high transparency in the UV region [39]

In this view, the present investigation deals with growth and characterization of L-Glutamic acid Zinc Chloride single crystal by slow evaporation solution growth technique and various nucleation parameters were determined The grown crystal was subjected to single crystal XRD, powder XRD, FT-IR, UV-Vis-NIR, SHG, TG/DTA, EDAX and Photoconducity studies

2 Experimental procedures

2.1 Material Synthesis

Commercially available L-Glutamic acid salt (AR grade, purity 99.8%) and Zinc chloride (AR grade purity 99.9%) were mixed with equimolar ratio (1:1) in a solvent of double distilled water at temperature 40 ºC The prepared solution was stirred well for about

10 hrs in order to obtain the homogenous solution The true chemical reaction of the title compound L-Glutamic acid Zinc chloride solution is shown below As grown L-glutamic acid zinc chloride crystal‟s molecular binding is shown in scheme 1

HO2CCH2CH2CH(NH2)CO2H+Zncl2 → Zn[HO2CCH2CH(NH2)CO2H]Cl2

L-Glutamic acid + Zinc chloride  L-Glutamic acid Zinc chloride

Scheme 1 Molecular structure of LGAZC crystal

2.2 Solubility

Solubility determination is essential in solution growth technique, since amount of solute in the solvent dictates the size of the crystal in growth process Hence, the solubility of the synthesised L-Glutamic acid Zinc chloride salt in double distilled water was determined

by gravimetric method This synthesized LGAZC solution was taken in an airtight container and kept at a constant temperature with continuous stirring (8hr) in a digitally controlled full-visibility constant temperature bath with temperature accuracy ±0.01 ºC After attaining the saturation, the equilibrium concentration of the solute is analysed graviometrically The solubility of LGAZC functions at seven different temperatures from 30 to 60 ºC was determined and the plot has been drawn as Temperature Vs Concentration shown in figure 1 From the plot, we observed that LGAZC has a positive temperature coefficient of solubility The increasing of solubility is due to the function of temperature and increasing of temperature (heat energy) breaks the bonds in to solids facilitating the dissolving reaction

Figure 1 Solubility curve for LGAZC

2.3 Nucleation Parameters

The nucleation parameters of LGAZC were evaluated The induction period of LGAZC recorded for different supersaturation ratios of 1.16, 1.20, 1.24, 1.28 and 1.32 The function of induction period versus supersatureation ratio is shown in the figure 2 The study

of induction period at different supersaturation levels gives an idea of the optimized induction period to have controlled nucleation rate to facilitate the growth of bulk size single crystals Experimental observations reveal that the induction period of LGAZC decreases as the supersaturation of the solution increases, hence the nucleation rate increases

The change in the Gibbs free energy (ΔG) between the crystalline phase and the surrounding mother solution results in a driving force, which stimulates crystallization According to classical nucleation theory the free energy required to form a spherical nucleus

is given by ΔG = (4/3) πr3

ΔGV + 4πr3γ, where, ΔGV is the energy change per unit volume, r

is the radius of the nucleus and γ is the interfacial energy The nucleation parameters such as,

ΔGV, γ and critical nucleus (r*) are calculated by using the well known formulate [40, 41] and the same are presented in Table 1.It is observed from the table that the nucleation rate increases with supersaturation ratio, which means the formation of higher number of nuclei with increased supersaturation The free energy barriers for formation of critical nucleus size decreased with increasing supersaturation ratio The nuclei will become stable and grow faster if the energy barrier is reduced at high supersaturation ratios The interfacial tension of LGAZC was estimated as 1.2563 mJ/m2 from the slope of ln τ and (ln S)-2 curve [42] (Figure 3) From the figure 4 and 5, we observed that the ΔG and r decreases with increasing supersaturation

1.14 1.16 1.18 1.20 1.22 1.24 1.26 1.28 1.30 1.32 1.34 100

200 300 400 500 600 700 800 900 1000

10 15 20 25 30 35 40 45 50 5.0

5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0

70 80 90 100 110 120

Table 1 Nucleation Parameters of LGAZC crystal

Crystal Supersaturation

S

Induction period 

sec

Interfacial tension () mJm -2

ΔG kJ/mole

2.4 Growth of LGAZC crystal

In accordance with the solubility data, the saturated solution of L-Glutamic acid Zinc chloride was prepared using double distilled water The solution was continuously stirred for

10 hours to avoid co-precipitation of multiple phases The stirred saturated solution was filtered using high quality Whattman filter paper and kept in an undisturbed place for evaporation at room temperature In a period of 50-70 days, seed crystals of LGAZC were formed due to spontaneous nucleation Optically good quality tiny crystal with perfect shape was selected as a seed to grow bulk size crystal Crystal having dimension upto 18x3x2 mm3was harvested in a period of 75 to 120 days As grown crystal of LGAZC is shown in figure 6 and the crystal has a needle shape with good transparency, defect free and no inclusion

Figure 6 As grown crystal of LGAZC crystal

3 Result and Discussion

3.1 Single crystal X-ray Diffraction Analysis

The grown L-Glutamic Acid Zinc Chloride crystal has been subjected to single crystal X- ray diffraction study using an ENRAF NONIUS CAD4 diffractometer with MoKα radiation (λ=0.71073 A˚ ) to determine the unit cell parameters It is observed from the single crystal XRD study that LGAZC crystal belongs to orthorhombic crystal system The calculated lattice parameter of L-glutamic acid zinc chloride crystal is compared with pure L-glutamic acid crystal and details are given in table 2 From the observation, there is a slight variations in the lattice parameters of LGAZC crystal which may be attributed by the presence of zinc chloride in the L-glutamic acid and whereas the structure of the L-glutamic acid was not be changed

Table 2 Crystal data of Pure L-glutamic acid and L-glutamic acid zinc single crystal

Pure L-glutamic acid crystal [43]

L-glutamic acid zinc chloride (LGAZC) crystal

3.2 Powder X-ray Diffraction Analysis

The powder sample of grown LGAZC was subjected to power X-ray diffraction study

to confirm its crystalline nature and structure The recorded powder XRD pattern of the LGAZC crystal is shown in the figure 7 The well defined Bragg‟s peaks were observed at specific 2θ angles (10º- 80º) shows high crystalline of LGAZC The measurement of lattice parameters from powder XRD pattern and peak indexing carried out using the software Proski version 2.The measured cell parameters from single crystal XRD is agreed well with powder XRD and results are compared in table 3

Figure 7 Powder X-ray diffraction analysis of LGAZC crystal

Table 3 Unit cell parameters of LGAZC crystal Parameters Single crystal

3.3 Fourier Transform Infrared Spectroscopic study

Infrared spectrum is an important record, which provides more information about the functional group of a compound In this technique almost all functional groups, in a molecule absorb characteristically within definite range of frequency [44-46] The absorption of IR radiation causes the various bonds in a molecule to stretch and bend with respect to one another The most important range (4000-500 cm-1) is of prime importance for the study of an organic and semi-organic compound by spectral analysis [47-48] The FTIR spectrum LGAZC is shown in figure 8 The peak observed at 3011 cm-1 corresponding to N-H stretching C-H and O-H bending vibration modes shows absorption peaks at 2950 cm-1 and

1498 cm-1 respectively The CO stretching vibration shows an absorption peak at 1304 cm-1

to 1043 cm-1 The COO plane deformation shows an absorption peak at 702 cm-1 The

presence of ZnCl2 in the FTIR spectrum is far below in the finger print region of the FTIR which may be the range 300-500 cm-1 The more functional group assignments of LGAZC crystal are given in table 4

Figure 8 FTIR spectrum of LGAZC crystal Table 4 FTIR functional group assignments of the grown LGAZC crystal

Wave number (Cm -1 )

Assignment L-Glutamic acid L –Glutamic Acid Zinc Chloride

2000 2500

3000 3500