Polymorphic ZnO has been prepared by a solution method at low temperature (40-90 A degrees C) and the product has been characterized by transmission electron microscopy, UV-vis absorption, and photoluminescence spectroscopy. It is found that the morphology and microstructure of ZnO can be tuned by varying the growth temperature and crystallization condition. The as-synthesized product exhibits narrowed band gap and strong orange luminescence at 620 nm, which may arise from the interstitial oxygen ion defect introduced into ZnO in the solution growth process.