Effect of malachite green dye doping in tristhiourea zinc (II) sulphate single crystal-a potential nonlinear optical material

Tristhiourea zinc (II) sulphate (ZTS) is a semi-organic and highly nonlinear optical material used for second harmonic generation (SHG) and other nonlinear optical (NLO) applications. The good quality of pure ZTS (PZTS) and 0.05 mol% and 0.1 mol% malachite green (MG) dye-doped ZTS crystals were harvested by employing low cost effective slow evaporation solution growth technique. The as-grown crystals were subjected to different characterization techniques to see the effect of MG doping on structural, mechanical, thermal, optical and NLO properties. The sharp and intense peaks observed in powder X-ray diffraction and high-resolution X-ray diffraction of PZTS and doped ZTS confirmed the good crystalline quality of pure and doped ZTS. A comparison of FT-IR spectroscopy studies of pure and doped crystals confirmed the incorporation of MG dopant in ZTS from the observation of shifting of various absorption bands. The optical bandgap energies and cut off wavelengths for pure and doped ZTS crystals were studied using UV-Vis.-NIR spectroscopy over an extended spectral range of 200-1100 nm at room temperature. The photoluminescence study revealed that microscopic defects like vacancies and self interstitials are reduced. Thermal stability of the grown crystals were studied by thermogravimetric analysis and found that the thermal stability is not affected much by doping. Vicker's hardness test was employed to pure and MG-doped ZTS crystals and elucidated that the doped ZTS crystals were found to be slightly softer than pure ZTS. The frequency dependent dielectric constants i.e. e(r) (real)(,)epsilon(i) (imaginary), dielectric loss (tan delta) and ac electrical conductivity (sigma(ac)) of pure and doped ZTS crystals were studied by subjecting the grown crystals with impedance analyzer. To observe the NLO property, the grown crystals were subjected to Kurtz powder technique. The results of SHG studies expounded that the SHG efficiency was increased by 2.75 times with MG doping in ZTS crystals.