Growth of L-asparagine monohydrate and its structural, optical, mechanical, thermal and electrical studies for nonlinear optical applications

Abstract

In the recent past, single crystals of organic materials exhibiting nonlinear optical behaviour have garnered much attention in the field of optical data storage and laser technology. In the present article, amino acid crystals of L-asparagine monohydrate (LAM) have been grown successfully by conventional slow evaporation solution growth technique from aqueous solution at room temperature (RT), with double distilled water used as a solvent. Single crystal x-ray diffraction was used to confirm the orthorhombic crystal structure (with P212121 space group) and lattice parameters of the grown crystal were determined. The crystallinity, purity, and phase of L-asparagine monohydrate were also determined from the powder x-ray diffraction data. The optical behaviour of LAM crystals was investigated by UV-Visible-NIR spectroscopy, and no absorption was found in the entire visible region. From the Tauc plot, the optical energy band gap was evaluated to be 5.09 eV. Valence band (EVB) and conduction band (ECB) positions of LAM were calculated from the knowledge of electron affinity (Ea), ionisation energy (Ei) of the elements and optical energy gap. Thermal parameters of the crystal were measured by photoacoustic spectroscopy. In addition, the mechanical stability of L-asparagine monohydrate single crystal was evaluated via shock damage threshold measurement. The dielectric studies as a function of frequency and temperature were carried out to understand the electrical behavior of the grown crystal. From the Z-scan analysis, nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of the LAM crystal were also determined.