Flower-like zinc oxide (ZnO) nanostructures with hexagonal crown were synthesized on a Si substrate by direct thermal evaporation of zinc power at a low temperature of 600 degrees C and atmospheric pressure. Field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and photoluminescence were applied to study the structural characteristics and optical properties of the product. The result indicated that the flower-like product with many slender branches and hexagonal crowns at the ends were single-crystalline wurtzite structures and were preferentially oriented in the < 001 > direction. The photo luminescence spectrum demonstrated a strong UV emission band at about 386 nm and a green emission band at 516 nm. The field emission of the product showed a turn-on field of 3.0 V/mu m at a current density of 0.1 mu A/cm(2), while the emission current density reached about 1 mA/cm(2) at an applied field of 5.9 V/mu m. (C) 2009 Elsevier B.V. All rights reserved.