Vertically aligned ZnO nanowires have been successfully synthesized on c-cut sapphire substrates by a catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD) in Ar and N2 background gases. In NAPLD, the nanoparticles formed in the background gas by laser ablation are used as a starting material for the growth of the nanowires. The surface density of the nanowires can be controlled by varying the density of nanoparticles, which are accomplished by changing the energy of the ablation laser, the repetition rate of the laser and so on. When single ZnO nanowire synthesized in a N2 background gas was excited by 355 nm laser-pulse with a pulse-width of 8 ns, stimulated emission was clearly observed, indicating high quality of the nanowire. These nanowires were used as building blocks for an ultraviolet photo-sensor, field emitters and an ultraviolet light emitting diode with a structure of n-ZnO/ZnO nanowire/p-GaN.