Effect of Cr doping on the structural and optical properties of ZnS nanoparticles

Zn1-xCrxS nanoparticles with x = 0.00, 0.005, 0.01, 0.02 and 0.03 were synthesized by chemical coprecipitation method at room temperature for the first time. Ethylene diamine tetraacetic acid was used as stabilizer. Energy dispersive analysis of X-rays confirmed the presence of Cr in the samples. The samples were characterized by scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy and optical absorption studies. XRD and selected area electron diffraction results showed that the samples of all compositions crystallized in cubic structure and the lattice parameters decreased linearly with increase in Cr content following Vegard's law indicating that the Cr ions have substituted for Zn in the ZnS lattice. The particle size estimated from XRD was in the range 6-10 nm. The optical absorption studies on the doped samples indicated that the absorption edge blue shifted with respect to those of bulk and nanocrystalline ZnS. The bandgap increased with increasing Cr concentration in a narrow range 3.81-4.03 eV. Photolumonesence studies showed blue emission with appreciable luminescence quenching with increasing Cr concentration. (C) 2011 WILEV-VCH Verlag GmbH & Co. KGaA, Weinheim