Growth, optical and electrical properties of l-lysine-L-tartaric acid (LLLT) nonlinear optical single crystals for electro-optic applications

Optically good quality single crystals of amino acid based organic l-lysine-L-tartaric acid (LLLT) have been grown by slow solvent evaporation technique at room temperature. The single crystal X-ray diffraction study confirms the grown crystal belongs to the noncentrosymmetric space group P2₁. The presence of various functional groups in the grown crystal has been identified by Fourier transform infrared spectroscopy. Optical transmission studies show that the grown crystal has a fairly wide transparency range which is suitable for nonlinear optical applications and the band gap energy of the sample is found to be 5.39 eV. Thermogravimetric and differential thermal analyses reveal that the crystal is thermally stable up to 201 °C. The second harmonic generation conversion efficiency of LLLT is closely three times that of potassium dihydrogen phosphate. The laser induced surface damage threshold for the grown crystal has been found to be 3.46 GW/cm². Normal indentation size effect was confirmed from micro hardness studies. Electrical conductivity behavior of the grown crystal was studied from the dielectric constant and dielectric loss measurement as a function of frequency with different temperatures. Photoconductivity studies of LLLT reveal its negative photoconducting nature. Also the ac and dc conductivity are measured and the results are discussed for the first time.