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Growth, Structural, Spectral, Opticaland
Photoconductivity Studies of Semiorganic Nonlinear
Optical Single Crystal: Calcium5-Sulfosalicylate
D Shalini, S Kalainathan, D Jayalakshmi
To cite this version:
Growth, Structural, Spectral, Opticaland Photoconductivity Studies of
Semiorganic Nonlinear Optical Single Crystal: Calcium5-Sulfosalicylate
66D. Shalini1, S. Kalainathan2, D. Jayalakshmi1
1 – PG and Research Department of Physics, Queen Mary’s College (A), Chennai, India 2 – School of advanced Sciences, VIT University, Vellore, India
DOI 10.2412/mmse.5.1.614 provided by Seo4U.link
Keywords: growth from solution, crystal structure, calcium compounds, nonlinear optical material.
ABSTRACT. Good quality semi-organic nonlinear optical crystal Calcium5-Sulfosalicylate (CA5SS) was synthesized,
and crystals were grown by slow evaporation solution growth technique. The cell parameters, molecular structure and crystalline perfection of the grown crystal were studied by single crystal x-ray diffraction analysis. The presence of various functional groups of the grown crystal was confirmed using Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) analysis. UV-Visible spectrum shows that CA5SS crystals have high transmittance in the range of 330–900 nm. The laser induced surface damage threshold, transient photoluminescence properties of the grown crystal were analyzed. The second harmonic generation efficiencies of the grown crystal (CA5SS) were studied and compared with that of KDP.
1. Introduction. Crystal engineering has the major purpose to understand the intermolecular
interactions and principle of packing in molecular crystals and also helps in the deliberate design of novel materials with NLO application targeted structures and properties. The hydrogen bonding ability helps to modification of the chemical compounds changes the optical properties of corresponding crystals. The lack of boundless π-electron delocalization, moderate optical nonlinearity, low optical transparency, and low laser damage threshold are the major limitations in organic nonlinear optical (NLO) crystals. In order to beat the above shortcomings, some new class of crystals such as semi-organic crystals have been developed. The coordination ability of organic acids towards the metal ions is currently of great significance, due to their usage in the materials research for optical and nonlinear optical (NLO) properties [1-2]. To achieve such goal, we have selected a derivative of salicylic acid, proton-transfer compounds of 5-sulfosalicylic acid, to explore its structural diversities and interesting topologies [3]. 5-sulfosalicylicacid (5SSA) is an attractive ligand, possessing three substituent groups such as the sulfonic acid (SO3H), the carboxylic acid (COOH)
and the phenolic groups (OH). The presence of the numerous oxygen atoms in three substituent groups usually results in hydrogen-bonding associations, and it can form mono, di and tri anionic ligand species through deprotonation, also the structures having significant interlayer π-π interactions between the cationic and anionic species [4]. In present work, we report for the first time on the growth and structure of Calcium 5-Sulfosalicylate single crystal using slow evaporation method.
2. Experimental procedure. CA5SS crystals were grown by slow evaporation solution growth
technique. The starting compounds, namely, 5-Sulfosalicylic acid dihydrate (Loba Chemie, 99%) and Calcium chloride dihydrate (Loba Chemie, 99%) were used without further purification. 5-Sulfosalicylic acid dihydrate and Calcium chloride dihydrate were mixed in the ratio of 2 : 1, and dissolved using deionised water as the solvent. The solution was stirred well for about 6 hours at room temperature and the saturated solution was filtered in clean beaker with Whatman filter paper
and kept undisturbed for crystallization to take place. Good quality single crystals of the title compound were obtained after 33 days. The grown crystal of CA5SS is shown in Fig. 1.
Fig. 1. As-grown CA5SS single crystals.
3. Results and discussion
3.1. Single crystal X-ray diffraction studies. The grown CA5SS crystal was confirmed by single
crystal XRD analysis. Single crystal X-ray diffraction studies were carried out using a Bruker AXS Kappa APEX II single crystal CCD diffractometer coupled with graphite-monochromated MoKα (λ=0.7107Å) radiation. Unit cell dimensions a = 5.5947(1) Å, b = 18.5055(2) Å, c = 9.9824(1) Å, α = 90°, β= 102.197(4)°, γ= 90°.
3.2. FT-IR studies: FT-IR technique is a useful method for detecting the formation of such
complexes like solids, liquids, gases, semi-solids, powders and polymers. The peak positions, widths, intensities and shapes all provide useful information. FT-IR spectrum of CA5SS crystal is shown in Fig.2. The FTIR spectrum of the CA5SS was recorded in the region 4000-500 cm−1 in the Stokes
region using the 1064 nm line of a Nd:YAG laser for excitation. The peak at 3019 cm-1 is ascribed to aromatic C-H Stretching. The peak at 1481 cm-1 due to C=C ring stretching vibration. C=O Stretching vibration of sulfosalicylate was observed at 1657 cm-1.The peak at 1355 cm-1 due to O-H In-plane
bending vibration. The peak at 736 cm-1 is due to S-O stretching vibrations. The band at 585 cm-1 is assigned to O-H Out-of-plane vibration.
Fig. 2. FTIR spectrum of CA5SS crystal.
3.3. UV-Visible analysis: UV–Vis study was carried out to understand the linear transmission The
selective electronic absorption spectrum of CA5SS crystal recorded absorption spectrum in the range 200-900 nm is shown Fig 3. Optically polished single crystal of thickness 1.2 mm was used for this study. The absorption spectrum shows the grown crystal has a lower cut-off wavelength at 330 nm, hence, the crystal shows minimum absorption and lower cut-off wavelength, and then the probability that the crystal is NLO active. This extensive range of transparency shows that the grown CA5SS crystal is a potential candidate for the optoelectronic applications and was free of volume defects.
Fig. 3.UV-Vis absorption spectrum of CA5SS crystal.
3.4. Laser damage threshold studies. The laser damage threshold of an optical crystal is an
important factor affecting its applications. It leads to the breakdown of the materials catastrophically damaging the maximum permissible power for a particular crystal defined as damage threshold. In the present experiment, an actively Q-switched Nd:YAG laser source with 10 ns pulse width and 10Hz repetition rate were used. The output intensity of the laser was controlled with variable attenuator and delivered to the test sample located at the near focusing of the converging lens. The energy density of the input laser beam was recorded using power meter till the crystal got damaged. The surface damage threshold of the crystal was calculated using the formula:
= ⁄ (1)
where = .
The laser damage threshold of CA5SS was measured 7.48×109 GW/cm2.The higher value of LDT will be useful for making laser based devices [5].
3.4. Photo conductivity studies. Photoconductivity of the grown CA5SS crystal was studied using
Keithley 485 picoammeter. Dark conductivity of the sample was studied by connecting the sample in series to a DC power supply and a picoammeter. Electrical contacts were made at spacing (d) of about 1.2 mm on the sample using silver paint. The DC input was increased from 50 to 450 V in steps and the corresponding readings in the electrometer were recorded. Photoconductivity studies were carried out by focusing light from a halogen lamp (100W) on samples. The variation of photocurrent (Ip) and
dark current (Id) with applied field is shown in Fig 4.
Fig. 4.Variation of current with applied field of CA5SS crystal.
The photocurrent of grown crystal is found to be less than the dark current at every applied electric field. This phenomenon is known as negative photoconductivity. This may attribute to their lifetime in the presence of radiation or the reduction in the number of charge carriers [6]
3.5. Nonlinear Optical Studies: SHG powder measurements were performed at room temperature.
The second harmonic generation efficiency of CA5SS crystal was measured by using Kurtz-Perry powder SHG technique [7] with potassium dihydrogen phosphate (KDP) crystal as reference material. The SHG efficiency obtained for CA5SS is about 0.7 times higher than that of potassium dihydrogen phosphate crystal.
Summary. The semi-organic nonlinear optical Calcium5-sulfosalicylate single crystals were grown
by slow evaporation solution growth technique. Single crystal X-ray diffraction analysis confirms the crystal belongs to a monoclinic system with space group P1n1. The modes of vibration molecule
groups present in the grown crystal were confirmed by FTIR spectral analysis. The lower cut-off wavelength and optical band gap energy of the grown crystal were examined by UV-Vis spectral analysis and it is suitable for potential device applications. The laser induced surface damage threshold value for CA5SS crystal was found to be 7.48×109 GW/cm2. Photoconductivity investigations reveal the negative photoconducting nature of CA5SS crystal. The SHG efficiency of the CA5SS crystal was found to be 0.7 times higher than that of standard KDP crystal.
Acknowledgment. One of the authors (D.JAYALAKSHMI) is grateful to the university grants
commission for support under minor research project scheme.
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0 50 100 150 200 250 300 350 400 450 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 C u rr en t (n an o a m p er e)
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