Optical and excitonic properties of crystalline ZnS nanowires: toward efficient ultraviolet emission at room temperature.

A systematic investigation into the excitonic properties of wurtzite ZnS nanowires (NWs) is presented. Under optical excitation, the ZnS NWs exhibit strong ultraviolet (UV) emission. Optical transition from free exciton A, free exciton B, and shallow level emission are observed and analyzed through power-dependent and temperature-dependent photoluminescence spectroscopy measurements performed from 10 to 300 K. The excitonic transition and coupling strength of exciton-longitudinal optical phonon were directly determined from the evolution of exciton peak energy and peak width broadening. Our studies indicate that free excitons in ZnS nanowires are very stable, suggesting a great promise for high-efficiency light-emitting devices and lasers in the UV region. Finally, the carrier dynamics of the ZnS NWs were measured and analyzed for the first time by ultrafast spectroscopy.