Enhancement of electro-optic and structural properties of TGS single crystals on doping with l-glutamic acid

Single crystals of pure and l-glutamic acid (LG) doped Triglycine Sulfate (TGS) crystals were grown by slow evaporation solution technique at ambient conditions. Effect of doping on various properties of the grown crystals was investigated. Powder X-ray diffraction (PXRD) studies confirmed the monoclinic system of crystal structure with lattice parameter a = ~ 9.28 Å, b = ~ 12.7 Å, and c = ~ 5.73 Å, and space group of P2₁. PXRD and Fourier-Transform Raman (FT-Raman) analysis confirmed that there is no new phase formation due to doping except a systematic variation in the intensity of the peaks in correlation with the morphology due to LG doping. The Raman bands obtained in the spectrum corresponds to NH₃ vibrations, the stretching vibrations of COO⁻, carboxyl vibrations, and vibrational modes of SO₄²⁻. Ultraviolet–Visible Spectroscopy (UV-Vis-NIR) analysis was carried out to see the changes in the optical transparency of pure TGS crystals due to LG doping. Optical band gaps (5.24 eV for PRTGS, and 5.07 eV for LGTGS) were calculated and found to decrease due to doping. The photoluminescence excitation and emission were studied. The thermal behavior of the grown crystal was investigated by Thermogravimetric analysis/Differential thermal analysis. Second harmonic generation (SHG) efficiency measurement showed the enhancement in the nonlinear optical characteristics of the as-grown pure and doped TGS single crystals. In the present study, the researchers found the good and comparable SHG efficiency with KDP in TGS crystals by LG doping for the first time. The surface morphology of the grown TGS single crystals was analyzed by using Scanning Electron Microscope. The mechanical studies showed the Mayer’s index (n) greater than 1.6 and thus predicting a soft-material nature of the as-grown crystals. The values of fracture toughness (K_c), brittleness indices (B_i), and yield strength (σ_ν) were estimated for the crystals. The dielectric constant and the dielectric loss decreased with an increase in the value of frequency. Hysteresis loop showed a negligible change in the doped TGS. The above studies reveal the effect of incorporation of LG into the lattice of TGS crystals.