The implantation of radioactive isotopes into semiconductor materials is a powerful technique that enables researchers to correctly assign chemical identities to defects observed by spectroscopic methods. Since each radioactive isotope has a characteristic decay rate, the intensity of spectroscopic features related to those atoms should also change with a corresponding rate, allowing an accurate identification of defect centres. This report shall discuss a number of Hg- and Au-related defects in silicon studied by Photoluminescence Spectroscopy. Radioactive 197Hg decays to stable Au, enabling defects involving both elements to be studied. Data presented here, based on implantations of 197Hg and stable 200Hg, confirms a previously observed Hg-related feature. It contains three Zero Phonon Lines and is due, we believe, to a three-level ground state and double excited states for the Hg atoms. The ‘FeB’ defect centre, previously shown to involve Au, is also studied. Whilst confirmation of the involvement of Au could not be established, an analysis has shown that thermal dissociation of this defect may negatively influence the results of spectroscopic measurements. A defect probably involving Au and Li is also studied, illustrating the techniques necessary to produce it. Again, this defect appears to dissociate upon room temperature storage at a rate similar to the ‘FeB’ defect, suggesting that Au is involved in this process for each. Finally, the results of an examination of Si:Ge Multi-Quantum Well (MQW) structures are presented. These indicate that much of the luminescence observed is related to either bulk- or surface-related dislocations in the Si rather than the quantum structures themselves.