Elsevier

Physica B: Condensed Matter

Volume 406, Issue 20, 15 October 2011, Pages 3856-3860
Physica B: Condensed Matter

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

https://doi.org/10.1016/j.physb.2011.07.011Get rights and content

Abstract

Good quality single crystals of pure and metal ion (Ni2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV–visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni2+doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni2+doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.

Introduction

Research in organic and inorganic functionalized nonlinear optical materials plays a crucial role because of their molecular interactions, bond strength, high molecular polarizability, easy incorporation of ions in the lattice, etc. [1], [2]. In the recent years there has been a growing interest in nonlinear optical materials due to their effective usage in the field of electro-optical devices, data storage technology and optical signal processing [3], [4]. However, semi-organic single crystals are attracting great attention in the field of nonlinear optics because of their high optical nonlinearity, chemical flexibility of ions, thermal stability and excellent transmittance in the UV–visible region [5], [6], [7]. Among the various classes of semi-organic nonlinear optical materials, metal complexes of thiourea have received potential interest, because they can be effectively used as the better alternatives for KDP crystals in the frequency doubling process and laser fusion experiments [8], [9]. As thiourea molecules possess a large value of dipole moment, they can form a number of metal coordination compounds like zinc thiourea chloride (ZTC), bis-thiourea cadmium chloride (BTCC), zinc (tris) thiourea sulfate (ZTS), tris-thiourea copper chloride (TCC), etc. [10], [11], [12]. Among these bis-thiourea zinc chloride (BTZC) is a desirable candidate for electro-optic and second harmonic generation devices, in view of its low angular sensitivity and high molecular interaction with intense light [13]. The spectroscopy of Ni2+ doped nonlinear optical materials has received much attention in the recent past in view of their enhancement in optical properties and molecular interactions [14], [15]. Hence in the present investigation attempts are made to grow optically transparent pure and metal ion doped BTZC single crystals by the slow solvent evaporation method. The grown crystals have been subjected to single crystal X-ray diffraction studies, powder XRD analysis, UV–visible transmission spectral analysis, energy dispersive spectroscopy analysis (EDAX), Vicker's hardness test and dielectric characterization. The SHG property of the pure and metal ion doped BTZC single crystals was confirmed by performing Kurtz powder test.

Section snippets

Material synthesis

Bis-thiourea zinc chloride (BTZC) was synthesized by mixing aqueous solution of zinc chloride and thiourea (99% pure) in the molar ratio 1:2. The reaction of synthesis is described by the equation,ZnCl2+2CS(NH2)2→Zn[CS(NH2)2]2Cl2The synthesized salt of the material was further purified by successive re-crystallization process using de-ionized water as solvent.

Crystal growth

The homogeneous solution obtained from the purified salt of the material is allowed to evaporate at room temperature. By spontaneous

Single X-ray diffraction studies

The grown crystals were subjected to single crystal X-ray diffraction analysis using a Bruker Kappa APEX-2 diffractometer with MoKα (λ=0.7170 Å) radiation to determine the lattice parameters and structure. The study reveals that both the crystals are crystallized in orthorhombic structure with space group Pn21a [16]. The lattice parameters calculated for the pure BTZC in the present work are in good agreement with the literature report [17]. However, for the Ni2+ doped BTZC crystal, slight

Conclusion

Optically transparent, good quality pure and Ni2+ doped bis-thiourea zinc chloride bulk single crystals were grown from aqueous solution by the slow solvent evaporation technique. The title material belongs to orthorhombic crystal structure with space group Pn21a. The slight variation in the cell parameters of the doped crystal reveals the incorporation of Ni2+ metal ions in the crystal lattice of pure BTZC. The crystallinity of the grown crystal was examined by powder X-ray diffraction

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