Defect induced modifications in the optical, dielectric, and transport properties of hydrothermally prepared ZnS nanoparticles and nanorods

Zinc sulfide nanoparticles (particles size range 10-20 nm) and nanorods (particles size range 20-35 nm) were prepared through a hydrothermal method. The influence of surface defects and lattice strain on the optical, dielectric, and electrical transport properties was investigated. The spectral shifts and modification in bandgap are explained based on effective mass approximation model. Photoluminescence and ESR studies clearly showed the presence of large density of surface defects in the samples. The Raman spectra were thoroughly studied using the Gaussian confinement model. Dielectric studies using impedance and electric modulus spectroscopy showed enhanced grain boundary conductivity. Both nanoparticles and nanorods were found to exhibit Cole-Cole type dielectric relaxation. The enhanced ac electrical conductivities observed in both the nanostructures were successfully explained using the correlated barrier hopping model. Parameters like hopping time, barrier width, and defect densities were calculated.