# Synthesis, Growth and Optical, Electrical, Thermal Properties of L-Proline Adipate Single Crystals for Nonlinear Optical Applications

N Indumathi, K Deepa, J Madhavan, S Senthil

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N Indumathi, K Deepa, J Madhavan, S Senthil. Synthesis, Growth and Optical, Electrical, Thermal Properties of L-Proline Adipate Single Crystals for Nonlinear Optical Applications. Mechanics, Materials Science & Engineering Journal, 2017, 9, 10.2412/mmse.5.76.497. hal-01503675

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# Synthesis, Growth and Optical, Electrical, Thermal Properties of L-Proline Adipate Single Crystals for Nonlinear Optical Applications

N. Indumathi¹, K. Deepa², J. Madhavan², S. Senthil¹, a

1. Department of physics, Government Arts College, Nandanam, Chennai-600035.

2. Department of physics, Loyola College, Chennai-600034, India.

a. indumathy.phy@gmail.com

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

DOI 10.2412/mmse.5.76.497 provided by [Seo4U.link](https://linkages.seo4u.com/10.2412/mmse.5.76.497)

**Keywords:** solution growth, single crystal XRD, UV-Vis-NIR, dielectric studies, TG/DTA and SHG.

**ABSTRACT.** Optically good quality L-Proline Adipate (LPA) crystals have been grown by slow evaporation method. The cell parameters of the grown crystal were determined by single crystal X-ray diffraction technique. The band gap energies of the LPA single crystals have been calculated and their cut off frequencies was determined from UV-vis NIR spectral analysis. The dielectric behaviour of grown crystals has been studied in the frequency range from 50Hz to 5MHz. The thermal behaviours were identified by TG/DTA analyzes. The second harmonic generation (SHG) efficiency was studied by using Kurtz powder technique.

**Introduction.** A major effort was developed to use the nonlinear optical (NLO) materials to generate different frequencies that are not available and also to develop the potential of tunable laser beams [1]. Many researchers have been focussed on the materials, which produce second harmonic generation, telecommunication, optical computing, optical data storage and optical information processing [2]. Amino acids with organic salts are prominent promising materials for the application of NLO devices [3]. These complexes are better alternative for KDP crystals in all respects. Growing single crystals with necessary properties is important in the field of laser technology. Hence great attention has been given to grow and characterize single crystals to modify their properties for the device fabrications [4]. L Proline is one of the two amino acids it contains α-amino, which is in the protonated $NH_2^+$ group and also contain α-carboxylic acid, which is in the deprotonated $COO^-$ group which create hydrogen bonds [5]. In the present work, we report the growth of L-Proline Adipate single crystals by slow evaporation technique. The grown LPA crystals were characterized by Single crystal XRD, UV-Vis-NIR spectroscopy, Dielectric Studies, Thermal studies and NLO studies.

**Experimental Procedure.** The commercially available L-Proline and Adipic acid salts were used to prepare the LPA single crystals by slow evaporation solution growth method at ambient temperature. The solution was prepared using deionised water as the solvent. The saturated solutions of L-Proline Adipate (LPA) were prepared separately and then the filtered solutions were taken in the ratio of 1:2. The mixed solution was stirred continuously using magnetic stirrer for 4 hours and kept in a dust free environment for evaporation. After 50 days, transparent LPA crystal of measuring 12x5x4 mm³ was harvested. The photograph of as grown single crystal of LPA is shown in Fig. 1.
<figure><img src="image_3.png" /><figcaption>Fig. 1. Photograph of LPA Single crystal.</figcaption></figure>

**Results and Discussion**

**Single crystal X-ray diffraction analysis.** The single-crystal XRD of LPA crystals were carried using ENRAF NONIUS CAD4 X-ray diffractometer. The cell parameters of LPA single crystal are a = 9.875(2) Å, b = 8.155(4) Å, c = 10.006(13) Å, α = γ = 90°, β = 110.038°, and volume = 856.1(3) Å³. The analysis of XRD data revealed that the grown crystals have been crystallised at monoclinic symmetry.

**UV – Vis – NIR studies.** The grown crystal has been characterized by UV-vis-NIR studies using Shimadzu UV 2450 spectrophotometer. The recorded Absorption spectrum is shown in Fig. 2. The spectrum analysis revealed that the high transparency and lower absorption cut off of 240 nm has been achieved in LPA crystal and then there was no absorption from 300nm to 1100nm it can be used for NLO device fabrications. The optical band gap of LPA crystal is shown in Fig. 3. The Energy band gap of LPA crystal is determined using the tauc's extrapolation method [6]. The band gap energy was found to be 5.2 eV for LPA crystals and thus indicate that the crystals are insulators and that can be used for laser technology.

<figure><img src="image_4.png" /><figcaption>Fig. 2. UV-vis-NIR Spectrum of LPA single crystal.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 3. Energy band gap of LPA single crystal.</figcaption></figure>

**Dielectric Measurements.** The dielectric measurements are one of the basic electrical properties of solids [7]. The study of dielectric constant and dielectric loss of a material gives an introduction about the nature of atoms in the solids, ionic nature and corresponding bonding in the material. The dielectric constant (ε<sub>r</sub>) and dielectric loss (tanδ) values obtained for LPA crystal are shown in Fig. 4 and Fig. 5 respectively. The increase in ε<sub>r</sub> at low frequency may be attributed to electric, ionic, orientation and space charge polarization and it decrease at high frequencies due to the loss of significance of these polarization gradually [8]. It has been found that the dielectric parameters (ε<sub>r</sub> and tanδ) values are found to decrease with the increase in frequency. This is a normal dielectric behaviour and it indicates that it can be used for NLO applications.

<figure><img src="image_6.png" /><figcaption>Fig. 4. Dielectric Constant of LPA Single crystal.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Fig. 5. Dielectric Loss of LPA Single crystal.</figcaption></figure>

**Thermal analysis.** Thermogravimetric and differential thermal analysis give information about the phase transition of the compound, crystallization of water and different decomposition stages of the crystal [9]. The TG/DTA of grown LPA crystal has been recorded in an atmosphere of nitrogen at a heating rate of 20°C/min in the temperature range of 30–600°C by using CNST thermal analyzer. The initial mass of the material subjected to the analysis was 2.474 mg. The recorded TG/DTA spectrum is shown in the Fig. 6. From the TG curve it is understood that the material is stable up to 157 °C indicating the absence of water molecules in the samples and hence the crystal rejected solvent molecules during crystallization, and on further heating the material suffers weight loss and it follows one stage weight loss pattern. The maximum decomposition mass loss of the material observed in between 200 °C and 300 °C. In the DTA curve, the endothermic peak observed at 154 °C is assigned to the melting point of LPA crystal it shows that the LPA crystal is in good crystalline nature. Hence, the material is stable upto 157 °C and it may be suitable for manufacturing the NLO devices.

<figure><img src="image_8.png" /><figcaption>Fig. 6. TGA/DTA curve of LPA Single crystal.</figcaption></figure>
**NLO Studies.** The second harmonic generation of the grown crystals was examined using the Kurtz and Perry powder technique [10]. The wavelength 1064 nm from a Q-switched Nd: YAG laser with a pulse energy 2.8mJ/pulse, pulse width 8 ns, and repetition rate of 10 Hz was used. The collected green emission from the LPA sample, the output confirms the nonlinear behaviour of LPA crystal. The output signal of 9.93 mJ was obtained for LPA single crystal compared to input signal of reference KDP is 8.91 mJ. Thus, the measured SHG efficiency was found that the grown LPA crystal has nearly 1.12 times higher NLO efficiency than KDP, which is familiar for organic NLO material.

**Summary.** The L-Proline Adipate (LPA) crystals have been grown by slow evaporation method at ambient temperature. The single crystal XRD confirmed the monoclinic symmetry of LPA crystals. The high transparency and lower cut-off wavelength (240 nm) of LPA crystal indicates the prominent potential for NLO device fabrications. The dielectric property studied at room temperature indicates that the dielectric constant and dielectric loss decreases with the increase in frequency. The characteristics of low dielectric loss with high frequency for LPA crystal indicates that the crystal possesses high optical quality with lesser defects and this parameter is vital for various applications of NLO materials. TG/DTA analysis show thermal stability of the materials up to 157°C, which is ambient temperature for NLO application. The existence of second harmonic generation (SHG) signal was observed by using ND: YAG laser with the fundamental wavelength of 1064 nm.

**References**

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Cite the paper

N. Indumathi, K. Deepa, J. Madhavan, S. Senthil, (2017). *Synthesis, Growth and Optical, Electrical, Thermal Properties of L-Proline Adipate Single Crystals for Nonlinear Optical Applications*. Mechanics, Materials Science & Engineering, Vol 9. DOI [10.2412/mmse.5.76.497](https://doi.org/10.2412/mmse.5.76.497)