Growth, optical, thermal and dielectric characterization of NLO active L-Tryptophan tris (4-nitrophenol) single crystals

This report discusses growth and characterization of an organic nonlinear optical (NLO) single crystal L-Tryptophan tris (4-nitrophenol) (LTT4NP). Good optical quality crystals of LTT4NP with dimension 4 × 3 × 1 mm³ were harvested by slow solvent evaporation method. Single crystal XRD measurements proved that the crystal belongs to monoclinic system with non-centrosymmetric space group P2₁. The optical absorption and transmission studies showed a desirable transparency window from 364 to 1100 nm with a wide optical band gap of 3.58 eV. The study explored a low refractive index of 2.111–2.112 from visible to IR region and low optical conductance below 3.5 eV indicating weak interaction of optical field with the material. The dielectric dispersion of the crystal and low dielectric loss at optical frequencies suggested positive attributes towards electro-optic applications. A highly dispersive a.c. conductivity was observed above 100 kHz which indicated strong polarization mechanism in higher frequencies. The Second Harmonic Generation (SHG) efficiency was estimated to be 2.2 times of KDP by Kurtz Perry technique. The crystal was found to be thermally stable upto 146 °C and mechanically stable upto a load of 30 g favouring the easy fabrication and processing.