Cu-substituted sulfur in nano-ZnS: structural, optical and electronic properties study

Nanosize ZnS1-xCux, (0.0 <= x <= 0.1) samples were prepared using a simple chemical procedure. X-ray phase analysis revealed a single-phase ZnS with a zinc blende structure for x <= 0.01, and then an additional minor ZnO wurtzite phase is formed for x >= 0.03. Rietveld structural analysis revealed Cu ions replacing Zn mainly substitutionally. The bandgap obtained from UV-Vis analysis showed a non-monotonic dependence on Cu content; it initially decreased and then increased to form a bandgap bowing. The same behavior is obtained for the lattice parameter obtained from Rietveld refinement. Fourier transform infrared technique was employed to investigate the different vibration bands in the samples. Photoluminescence (PL) analysis demonstrated obviously the dependence of the emitted colors on both the amount of Cu-doping and the excitation wavelength; the PL intensity has a maximum intensity for 1% Cu-doping. Density function theory calculations were used to investigate the influence of copper substitution for sulfur in ZnS on different electronic parameters.