Crystal structure, spectroscopic, thermal, mechanical, linear optical, second order and third order nonlinear optical properties of semiorganic crystal: l-threoninium phosphate (LTP)

An optically good quality semiorganic single crystal of l-threoninium phosphate (LTP) was grown by solvent evaporation technique at room temperature. Single and powder XRD revealed the orthorhombic crystal structure of LTP with non-centrosymmetric space group Pna21. Linear optical behaviour of the title crystal was realized using UV–visible spectroscopy. The lower cut-off value was found to be 200 nm with broad optical transparency in entire visible region. Functional group and its bonding nature in the titular compound are explored by FTIR spectroscopic analysis. The LTP is thermally stable up to 241 °C and deferent level of decompositions with respect to temperature was analyzed using TG/DTA. Mechanical properties of LTP were studied using Vickers’ microhardness tester. The fracture toughness (Kc), Knoop hardness (Hk), brittleness index (Bi) and elastic stiffness constant (C11) of LTP were calculated using micro-indentation data. Laser damage threshold value of LTP was found to be 4.92 GW/cm2 which is convincingly high to use the crystal in lasing applications. The second harmonic generation efficiency of LTP is 2.1 times greater than the conventional KDP crystal. The nonlinear refractive index (n2), the nonlinear absorption coefficient (β) and third-order nonlinear susceptibility (χ(3)) of the title crystal was found to be 1.19 × 10−15 m3/W, 4.742 × 10−9 m/W and 5.382 × 10−14 m/W (esu) respectively. The single beam Z-Scan unit equipped with 532 nm continues wave laser was used to measure the third-order nonlinear optical parameters of grown crystal.