The effect of Cr3+doping on the crystalline perfection and optical properties of zinc tris(thiourea)sulfate, a nonlinear optical material

A study of the effect of Cr3+doping in zinc tris(thiourea)sulfate (ZTS, a well known nonlinear optical material) single crystals on crystalline perfection and optical properties was carried out. Pure and chromium-doped (1 and 2 mol%) ZTS single crystals were grown by the slow evaporation solution technique. The actual concentration of chromium incorporated into the crystal lattice was found to be different, as evaluated by flame atomic absorption spectroscopy. High-resolution X-ray diffraction (HRXRD) analysis revealed that chromium doping led to the creation of vacancies in the grown single crystals. The photoluminescence emission spectra of pure and doped crystals supported the HRXRD findings. The optical band gap of the single crystals increased as a result of the Cr3+doping, but their transparency in the visible region decreased. The doped crystals exhibited higher linear refractive indices than the pure crystals. The optical dielectric constant (∊), the extinction coefficient (k), the average single-oscillator energy for electronic transitions (Eo) and the oscillator strength (Ed) were evaluated for ZTS single crystals and significant changes were observed in these parameters due to the Cr3+doping.