A direct correlation of structural and optical properties in ZnO epitaxial layers has been achieved on a microscopic scale using highly spatially and spectrally resolved cathodoluminescence. The surface morphology of the high-quality ZnO layers is characterized by a distinct hexagonal domain structure. While the laterally averaged cathodoluminescence spectrum shows intense and narrow I-8 luminescence, a distinct emission line at the spectral position of I-0/I-1 emerges in the local spectra taken at domain boundaries. In contrast, no I-0/I-1 emission is found inside the domains. Monochromatic images further evidence the selective incorporation of impurities at the grain boundaries of domains. Monochromatic images of the I-8 peak wavelength directly visualize the strain relaxation across the domains towards their very center, where a drop in quantum efficiency indicates enhanced defect concentration. (C) 2004 Elsevier B.V. All rights reserved.