Optical properties in Mn-doped ZnS thin films: Photoluminescence quenching

Mn-doped ZnS thin films are synthesized on soda-lime glass substrates using magnetron co-sputtering technique. X-ray diffraction and atomic force microscopy measurements indicate that of the as-obtained films including the highest Mn (~11% relative to the Zn concentration) in the lattice of ZnS are amorphous with a granular morphology. X-ray photoelectron spectroscopy reveals the presence of Zn²⁺, Mn²⁺ and S^2- chemical states in the films. The undoped ZnS film exhibits photoluminescence (PL) peaks at energies around 3.26 eV (wavelength ~379 nm) and 2.95 eV (~420 nm), which originate from the interplay between excited electron, defect (sulfur vacancy) states and the valence band. For the Mn-doped ZnS films, the band-to-band emission peak is quenched and shifts toward to higher energies at a rate of 11.7±2 meV/Mn%. We propose that Mn dopant-mediated structural phases and non-radiative deep traps in ZnS cause the modification in the optical transition.