Optical processes in the formation of stimulated emission from ZnO nanowires

This paper studies power dependent photoluminescence spectra, thestimulated emission occurring at ultraviolet (UV) band instead of thegreen emission band of ZnO nanowires, which are prepared with achemical reduction method. The dynamics of the UV emission and greenemission is given to demonstrate the reason of stimulated emission occurring at UVband but not the green emission band under high excitation, which indicatesthat the slow decay rate of trap state makes it easy to be fully filled andsaturated, while the fast decay rate of near-band-edge exciton state makesthe UV emission dominate the radiative recombination under high excitation.The UV emission, as well as the corresponding stimulated emission, occurs incompetition with the green deep-trap emission. In addition, when pumpfluence further increases, the multiple lasing modes appear. The dependenceof these lasing modes on the pump fluence is first discussed. This diagramshould be helpful to understand and design the optical nanodevices of ZnOnanowires.