Zinc oxide (ZnO) epilayers were grown on (0 0 0 1) sapphire substrates by reactive sputtering of a zinc target at substrate temperatures of 300 and 600 degrees C. High-resolution X-ray diffraction, UV-visible and photoluminescence (PL) measurements were carried out to obtain information about epitaxy, microstructure and optically active defects in these epilayers. Though the epilayer deposited at 600 degrees C showed a slightly smaller crystallite size along the growth direction as compared to that deposited at 300 degrees C, it was much superior in terms of other micro-structural parameters. It exhibited significantly small values of micro-strain (2 x 10(-4)), rocking curve width (similar to 0.13 degrees), mosaic twist (0.35 degrees), and screw (6.6 x 10(8) cm(-2))- and edge (2.9 X 10(11) cm(-2))-type dislocation densities. Absorption and PL studies showed the high optical quality of the ZnO epilayer deposited at 600 degrees C, which exhibited a narrow (full-width at half-maximum-FWHM similar to 96 meV) and intense band edge luminescence at room temperature. The micro-structural parameters and the sharp PL peak show that the reactively sputtered ZnO epilayer grown at 600 degrees C is comparable in epitaxial and optical quality with ZnO grown by other epitaxial processes. (C) 2008 Elsevier B.V. All rights reserved.