Photoluminescence measurements of cadmium-implanted and aluminium-doped oxygen-rich silicon are presented in this thesis. Temperature dependence, uniaxial stress and Zeeman measurements were carried out on all the defects reported. In the case of cadmium-implanted silicon, three new cadmium related defects are reported with zero phonon lines at ~ 1026meV, 983 meV and 935 meV. Temperature dependence studies indicate that the thermal binding energies of all the defects are in the range 13-17meV and no excited thermalising states are seen for the 983meV and 935meV lines. The 1026meV line shows clear evidence of an excited state at higher energy (-1.1 meV). Uniaxial stress measurements reveal rhombic I (C2v) symmetry for the 1026 meV and 983 meV lines. The 935 meV line is tentatively ascribed to monoclinic I symmetry. None of the cadmium-related lines show either a shift or splitting in magnetic fields up to 5 Tesla. Cadmium isotope substitution studies reveal the involvement of a single cadmium atom in each defect. Circumstantial evidence indicates the involvement of oxygen in the defects, as none of the defects are observed in oxygen lean silicon. The relationship between these cadmium-related defects and previously reported zinc-related defects is discussed. In the case of aluminium-doped silicon, a previously reported defect with a zero phonon line at 922meV was investigated further. Measurements as a function of temperature reveal that the thermal binding energy is ~15meV and no evidence of thermalising states is seen. Uniaxial stress measurements reveal a low symmetry configuration for the 922meV line (monoclinic I, Clh). This line neither shifts nor splits under magnetic fields of up to 5 Tesla. Similiarities in the behaviour under uniaxial stress of this defect and a previously reported aluminium-related defect are presented.