Well-aligned ZnO nanorod and nanobolt arrays were synthesized on p-type Si(100) substrates by a simple physical vapor deposition method. During the growth process when the carrier gas was switched from Ar to air, the nanorods changed into nanobolts completely. The mechanism for this transformation process is discussed. The room-temperature photoluminescence spectrum of nanobolts showed a strong ultraviolet emission at 3.26 eV coupled with a weak deep level energy emission at 2.48 eV. The origin of the ultraviolet emission of nanobolts was investigated by temperature-dependent photoluminescence spectra.