Effect of organic dopants on ZTS single crystals

The influence of organic dopants on tristhioureazinc(II)sulphate (ZTS) single crystals from aqueous solutions at 30 °C is investigated. The dopants used in the present investigation are disodium salt of ethylenediamminetetraacetic acid (EDTA), benzene and 1,10-phenanthroline (Phen) which are having different structures. Though, all the dopants show better results, prominent influence is observed in case of EDTA dopant with low concentration of 5×10−3 M L−1 and hence the results pertaining to EDTA dopant are described in detail in the present article. At low concentrations of dopant, an increase in the metastable zone width, leading to an increase in the crystal growth rate is observed. At higher dopant concentration, growth rate decreases. The crystalline perfection of the grown crystals has been evaluated by high-resolution X-ray diffractometry (HRXRD). The diffraction curve (DC) of a typical EDTA-doped as-grown ZTS crystal was observed to contain one additional peak very close to the main peak suggesting the possibility of an epitaxial layer on the surface of the crystal. After removing this layer by lapping followed by chemical etching, the DC was found to contain only a single and very sharp peak showing that the main crystal is having a much better crystalline perfection than that observed for the specimen grown with out using any dopant in the solution. This indicates that the complexation of trace metal ion impurities (present in the solution) with the dopants is responsible for the formation of the layer on the surface of the crystal and prevents the entry of impurities in the growing crystal. The complexation also promotes the growth process leading to a rapid growth with high crystalline quality. Not much variation is observed in FT-IR and XRD of pure and doped ZTS. However, second harmonic generation (SHG) efficiency measurements carried out with different dopants reveal that nonlinear optical (NLO) property is enhanced by EDTA and benzene dopants. However, Phen depresses the NLO efficiency of ZTS.