By employing an insulating zinc oxide (i-ZnO) as an electron accelerating layer, and an n-type ZnO as an active layer, ultraviolet (UV) emissions at 385 nm caused by the excitation of the n-ZnO layer by the accelerated electrons from the i-ZnO layer have been realized. By replacing the active layer with larger bandgap Mg Zn O and properly optimizing the structure, shorter wavelength emissions at around 328 nm have been obtained. Considering that the p-type doping of wide bandgap semiconductors is still a challenging issue, the results reported in this Letter may provide a promising alternative route to UV emissions.