The effect of cobalt-doping on some of the optical properties of glycine zinc sulfate (GZS) single crystal

Glycine zinc sulfate (GZS) single crystals, pure and doped with three different ratios of cobalt ions were synthesized and grown by the slow evaporation technique of aqueous solutions at 34 deg. C. Optically transparent single crystals with dimensions up to 2x1.5x1.2 cm3 were obtained in about four weeks. The optical transmittance was measured and used to study some optical properties for these crystals. Pure GZS crystal has high optical transmittance in the whole visible range and UV transparency with lower cut off wavelength at 300 nm. By adding Co-ions to GZS crystal, the transmittance decreases and the value of cut off shifts to the higher wavelengths with increasing Co ratio. Adding Co-dopants to GZS crystal has other effects like increasing the magnitude of the absorption coefficient (α) and forming an absorption band around 2.1 eV. The height of this absorption band increases with increasing Co ratio. The optical energy gap (Eg) for pure GZS crystal is about 3.80 eV. This value decreases with increasing Co ratio to GZS crystals. The predominant optical transition for pure and Co-doped GZS crystals is the allowed indirect one. The phonon energy (Ep) and the phonon equivalent temperature (Tp) at room temperature are 0.20 eV and 2318.84 K for pure GZS crystal, respectively, and these values increase with increasing Co content in GZS crystals.