# Optical, Thermal and Electrical Studies on L-Malic Acid Doped ADP Single Crystals for Non-Linear Optical Application

S Arulmani, K Deepa, N Indumathi, M Viktor Antony Raj, S Senthil

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S Arulmani, K Deepa, N Indumathi, M Viktor Antony Raj, S Senthil. Optical, Thermal and Electrical Studies on L-Malic Acid Doped ADP Single Crystals for Non-Linear Optical Application. Mechanics, Materials Science & Engineering MMSE Journal. Open Access, 2017, 9, 10.2412/mmse.30.76.146. hal-01503652

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# Optical, Thermal and Electrical Studies on L-Malic Acid Doped ADP Single Crystals for Non-Linear Optical Application

S. Arulmani¹, K. Deepa², N. Indumathi¹, M. Victor Antony Raj², S. Senthil¹, a

1. Department of Physics, Govt. Arts College for Men (Autonomous), Nandanam, Chennai, India

2. Department of Physics, Loyola College, Chennai, India

a. ssatoms@yahoo.co.in

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.30.76.146 provided by [Seo4U.link](https://seo4U.link)

**Keywords:** PXRD, FT-IR, NLO studies, UV-visible, TGA/DTA, dielectric studies.

**ABSTRACT.** Ammonium Dihydrogen Phosphate (ADP) is one of the most popular crystals used for nonlinear optical (NLO) applications. ADP crystal is of more appeal due to its piezo-electric property. ADP crystals attract more interest because of their unique nonlinear optical, dielectric and anti-ferroelectric properties. The L-Malic acid doped ADP (LMADP) single crystals were grown by slow evaporation method at room temperature. The Crystalline nature of the grown LMADP crystal has been studied by powder XRD analysis. A Fourier transform infrared (FT-IR) study confirms the functional groups of the crystals. The second harmonic generation efficiency of the crystals was determined by NLO studies. The UV-visible study confirms the wide optical transmittance window for the doped crystals imperative for optoelectronics applications. TG/DTA analyses were carried out to characterize the melting behavior and stability of the title compound. The electrical properties of the grown crystal have been analyzed by dielectric constant and dielectric loss with frequency.

**Introduction.** Ammonium dihydrogen phosphate (ADP) is a well-known anti-ferroelectric crystal. The study of ADP crystal is very interesting in view of the dielectric, piezo-electric and optical properties. Growth and studies of ammonium dihydrogen phosphate (ADP) crystal is a favorite topic to researchers because of its unique properties and wide applications. Single crystals of ADP are used for frequency doubling and frequency tripling of laser systems, optical switches in inertial confinement fusion and acoustic-optical devices [1,2]. ADP has been the subject of a wide variety of investigations over the past decades. Reasonable studies have been done on the growth and properties of pure ADP. In the light of the research work being done on ADP crystals, to improve the properties, the present work focuses on L-malic acid as a dopant in ADP and this is expected to enhance the nonlinearity of the crystal. In the last decades, many researchers have tried to found varieties of new NLO materials for laser applications [3]. Nonlinear optical (NLO) materials play a major role in information technology and industrial applications. L-Malic acid doped with ADP will be of special interest as a fundamental building block to develop complex crystal with improved NLO properties. The grown crystals were characterized by PXRD, FTIR, TG/DTA, Dielectric studies, UV-vis spectroscopy and NLO Studies.

**Experimental Procedure.** L-Malic acid of 0.3% has been doped with pure ADP (Ammonium dihydrogen phosphate). The calculated amount of salts was dissolved in double dissolved water. This solution was then stirred well for more than four hours and filtered using Whatmann filter paper. The pH value of the reaction mixture was monitored. It was porously sealed and placed in a dust free atmosphere for slow evaporation at room temperature. Optically transparent crystals were harvested within 30 days. The photograph of as grown doped LMADP crystal is shown in Fig. 1.

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license
http://creativecommons.org/licenses/by-nc-nd/4.0/
<figure><img src="image_3.png" /><figcaption>Fig. 1. As grown single crystal of LMADP.</figcaption></figure>

**Result and Discussion.**

**Powder X-ray Diffraction Analysis.** X-ray diffraction technique is a powerful tool to analyze the crystalline nature of the materials. Powder X-ray diffraction analysis was carried out by using XPERTPRO X-Ray diffractometer with CuKα radiation (λ=1.5406 Å). The samples were scanned over the range 10-70° as shown in the Fig. 2. The cell parameter values for LMADP are a=b=7.406Å, c=7.526Å with the angles α = β = γ = 90°. The present result is in close agreement with the reported results [4]. The structure of LMADP crystal is tetragonal. The sharp and well defined peaks at specific 2θ values indicate the high crystalline nature of the crystal.

<figure><img src="image_4.png" /><figcaption>Fig. 2. Powder XRD pattern of LMADP crystals.</figcaption></figure>

**FT-IR Analysis.** FT-IR spectra of LMADP crystal were recorded in range of 450-4000cm⁻¹ by KBr PELLET technique. The functional groups of L-Malic acid doped with ADP crystals have been identified and it was shown in Fig 3. The characteristic peaks of functional groups of LMADP are observed at 3236, 1167, 973 [5]. The broad band in the high energy regions is due to the O-H vibration of water, P-O-H group and N-H vibration of ammonia. The peaks at 1101 and 908 cm⁻¹ represent P-O-H vibrations. The PO₄ vibration gives their peaks at 547 and 499 cm⁻¹. The bending vibration of water gives it peak at 1646 cm⁻¹ in IR. The peak at 1402cm⁻¹ is due to bending vibrations of ammonium. The vibrational band at 3245 cm⁻¹ was also assigned to the vibration of N-H band. The C-O stretching mode of vibration and O-H in-plane bending modes of vibration is observed at 1213 cm⁻¹ [6]. The PO₄ vibration of the parent is shifted from 611to 481 cm⁻¹, which was confirm by the presence of L-Malic acid on the lattice of ADP crystals.
<figure><img src="image_5.png" /><figcaption>Fig. 3. FT-IR spectral analysis of LMADP Crystal.</figcaption></figure>

**SHG Analysis.** Kurtz and Perry techniques [7] were employed to measure the SHG efficiency of the grown crystals in reference with the pure KDP. In the measurement, Q-switched Nd:YAG laser of wavelength 1064nm of peak power 2.35 mJ, pulse duration 8 ns and repetition rate 10Hz was used. Output intensity of SHG gives relative values of NLO efficiency of the material. The output energies from the grown sample and reference KDP are found to be 21.2 mW and 19.6 mW respectively. It is found that the SHG efficiency is 1.08 times greater than that of standard KDP.

**Optical Absorption Studies.** The UV-Vis spectrum of LMADP crystals were recorded using Perkin Elmer UV-Vis spectrometer (Model: Lambda 35) in the wavelength range of 200-900 nm. Optically polished single crystals of thickness 3mm were used for this study. Fig. 4. shows that the absorption spectrum of the grown crystals and the cut-off wavelength is found to be 220 nm. The presence of lower cut off wavelength and the wide optical transmission window range of the materials possessing NLO activity. The good transmittance property of the crystal in the entire visible region ensures its suitability for second harmonic generation application [8]. The optical band gap energy value is found to be 4.68 eV from Fig. 5.

<figure><img src="image_6.png" /><figcaption>Fig. 4. UV-vis absorption of LMADP Crystal.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Fig. 5. UV-vis band gap of LMADP Crystal.</figcaption></figure>

**Thermal Analysis.** The thermal behavior of LMADP was studied by the Thermogravimetric (TG) and differential thermal analyses (DTA) recorded using PerkinElmer Diamond TG/DTA instrument. Differential thermogram analysis (DTA) and Thermogravimetric analysis (TGA) give information regarding phase transition and different stages of decomposition of the crystal system. The thermal analyses are used to found out the weight loss (TGA), melting and decomposition point (DTA) of the grown LMADP single crystal. The DTA curve of LMADP has a major endothermic peak at 208° C. It coincides with the weight loss in the TGA trace. The endothermic peak at 208° C represents the melting point of the compound. Another important observation is that, there is no phase transition and color change till the material melts and this enhances the temperature range for the utility of the crystal for NLO applications. It is observed from the literature that the presence of "higher decomposing temperature doping increases the thermal stability of the compound [9].

<figure><img src="image_8.png" /><figcaption>Fig. 6. TG-DTA spectrum of LMADP Crystal.</figcaption></figure>

**Dielectric Studies.** The dielectric analysis is an important characteristic that can be used to fetch knowledge based on the electrical properties of a material medium as a function of temperature and frequency. Based on this analysis, the capability of storing electric charges by the material and capability of transferring the electric charge can be assessed. Dielectric properties are correlated with electro optic property of the crystals particularly when they are non-conducting materials [10]. The value of dielectric constant decreases with the increase in frequency and becomes constant at higher frequency. The high value of dielectric constant in the low frequency region may be due to the contribution from all four polarizations namely, electronic, ionic, orientation and space charge polarization and its low value at higher frequency may due to the loss of significance of these polarizations gradually.
<figure><img src="image_9.png" /><figcaption>Fig. 7. Dielectric constant Vs Log f of LMADP Crystal.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Fig. 8. Dielectric loss Vs Log f of LMADP Crystal.</figcaption></figure>

**Summary.** A novel organic single crystal of LMADP was grown from aqueous solution by the slow evaporation method. The crystal structure was confirmed by single-crystal XRD analysis and the FTIR trace reveals the presence of functional groups. The UV cut-off wavelength of LMADP crystal is found to be 220 nm and the band gap is 4.687 eV. TGA/DTA confirms that the sample is stable up to 208 °C. The SHG efficiency of LMADP crystal is 1.08 times greater than that of the KDP. The low dielectric constant and dielectric loss of LMADP at higher frequencies show that the material is a more suitable candidate for nonlinear optical application.

**References**

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Cite the paper

S. Arulmani, K. Deepa, N. Indumathi, M. Victor Antony Raj, S. Senthil (2017). *Optical, Thermal and Electrical Studies on L-Malic Acid Doped ADP Single Crystals for Non-Linear Optical Application*. *Mechanics, Materials Science & Engineering*, Vol 9. DOI [10.2412/mmse.30.76.146](https://doi.org/10.2412/mmse.30.76.146)