Effect of phosphorous on the growth, optical, mechanical and thermal properties of L-alanine crystals

Abstract

Abstract-Single crystals of L-alanine were grown from aqueous solution with a small amount of orthophosphoric acid (H3PO4). The single crystal X-ray diffraction (XRD) analysis was employed to identify the cell parameters. The grown crystal was characterized by Energy Dispersive X-ray (EDX) spectrum. The UV-visible transmittance was recorded. The presence of a functional group was confirmed by FTIR analysis. The TGA/DTA studies showed the thermal properties of the crystals. The mechanical strength was analyzed by measuring microhardness of the grown compounds. The second harmonic generation of grown crystals was confirmed by the KurtzPerry method using an Nd:YAG laser.Nonlinear optical (NLO) materials capable of generating the second harmonic frequency play a major role in the domain of optoelectronics and photonics [1]. Due to their large nonlinearity, low cut-off wavelengths, high thresholds and short response time to laser power, NLO materials are attracting much attention for possible use in optical devices. In particular, efforts have been made on pure amino acid and their complexes like L-, L-histidine bromide [7], etc. Among the amino acids, L-alanine is the simplest molecule having second harmonic generation (SHG) efficiency, of which one third if that of well known potassium dihydrogen phosphate (KDP) [8].Phosphoric acid as a dopant has been found to yield crystals with a large plane area useful for IR detector applications [9,10]. Even at a very low concentration level of orthophosphoric acid, there has been reported [11] a significant improvement in the pyroelectric coefficient, lowering of dielectric permittivity at a transition temperature (T c ) and an increase in the coercive field of the triglycine sulphate (TGS) crystal. The influence of H 3 PO 4 dopant concentration on the TGS crystal growth and properties has been studied and the main objective has been to optimize the dopant concentration effective for an IR applications [12]. The presence of orthophosphoric acid in L-valine crystal exhibits improved mechanical strength and SHG [13]. * E-mail: chezhiyan70@gmail.com An attempt has been made to study the effect of acids on the optical, mechanical and thermal properties of Lalanine. Current investigation has been focused the effect of H 3 PO 4 on L-alanine growing from aqueous solution. The starting material was synthesized by adding orthophosphoric acid (1ml) to the high purity L-alanine (2.23g) salt, taken and dissolved in 25ml of deionized water in a beaker. The mixed solution was slightly heated and stirred continuously for 8 hours. After that the saturated solution was filtered and then prepared in a crystallizing vessel with perforated covers. It was kept in a constant temperature bath in undisturbed conditions to maintain a temperature of 35ºC. After the growth period of one week, good quality transparent crystals were obtained from the saturated aqueous solution of L-alanine in the presence of H 3 PO 4 . Figure 1 shows the photograph of the grown crystal. Single crystal X-ray diffraction ...