A series of electron irradiations has been performed on diamond and 4H SiC single crystal specimens. A wide range of different doses and dose rates was investigated. In addition, a more limited investigation of localized hydrogen and helium implantation of 4H SiC has been made. The electron energies were sufficient to cause atomic displacements creating vacancies and self-interstitials in the irradiated samples. After electron-irradiation or implantation the samples were studied by low temperature (∼7 K) photoluminescence microscopy. It was found that some of the defect centres migrated over large distances outside of the irradiated regions and that this distance increased with increase of the dose. Two possible explanations for this remarkable behaviour are discussed. One is based on the absorption by the defects of light created by recombination of electrons and holes in the irradiated or implanted region. The other deals with the consequences of recombination-enhanced migration at point defects that traps carriers as they are driven out of the irradiated region by electric fields created during the irradiation or implantation process. Interstitial atoms are deduced as migrating further than vacancies in this process.