The orientation of defect pairs with respect to the crystallographic axes was determined in ZnO. In a specific orientation of the strain with respect to the c axis of the crystal and the k-vector, the defect pair emission lines split, owing to combined strain and spin exchange. The polarization of the split components combined with knowledge of the specific orientation of the crystal and the k-vector allows one to determine the orientation of the defect pairs in the crystal. (C) 1999 Elsevier Science Ltd. All rights reserved.