Dielectric properties and second harmonic generation of glycine doped bisthiourea cobalt and nickel malonates as new semiorganic non-linear optical materials

Abstract

A new class of materials viz. glycine doped bisthiourea cobalt malonate (BTCoM-Gly) and glycine doped bisthiourea nickel malonate (BTNi-Gly) have been synthesized by simple solvent free mechanochemical method. The chemical composition was evaluated by chemical and elemental analysis. Incorporation of glycine in compound was confirmed by EDAX and FTIR techniques. FTIR studies also ascertained the coordination of metal ion to thiourea through sulphur atom. SEM images showed that both the compounds have linear array type morphology. Thermal stability of material has been investigated by TG and DTA showing BTNiM-Gly is more stable (74.85 °C). Transmittance spectra reveals that lower cut-off wavelength of BTCoM-Gly is 296 nm and that of BTNiM-Gly, 298 nm, indicating to have a good optical transmission in entire visible region, which is desired characteristic for non-linear optical (NLO) materials. The dielectric measurements of the compounds were accomplished with varying frequencies at ambient temperature. Dielectric constant and dielectric loss values of both compounds were decreased with the increase in frequency which ultimately enhanced the second harmonic generation (SHG) efficiency. The SHG conversion efficiency was measured by modified Kurtz-Perry powder technique and found to be 0.751 nm and 0.610 nm times higher than standard KDP for BTCoM-Gly and BTNiM-Gly respectively. The higher SHG conversion efficiency of the compounds illustrates non-linear optical nature of materials and their suitability for NLO applications.