Thermal quenching behavior of emission bands in Eu-doped ZnS nanowires

Optical properties and temperature-dependent quenching behaviors of emission from undoped and Eu-doped ZnS nanowires (NWs) were characterized. Electron paramagnetic resonance measurements confirmed the presence of the dopant in valence state Eu²⁺. The 368 nm (3.37 eV) near-band-edge emission band associated with dissociation of a bound exciton was found to have an activation energy of 27.3 meV. A dopant-related transition was observed from both samples due to the incorporation of unintentional Au catalyst in the undoped NWs and of intentional Eu-dopant. These dopant-related transitions show large activation energy and appreciable amount of emission intensities above the room temperature. Both samples also exhibit surface-state-related transitions around 400 nm (3.046 eV) which have relatively smaller activation energies than the dopant-related transitions.