Photoluminescence (PL) spectroscopy is used to investigate the optical properties of a beryllium related defect in silicon. Bound exciton recombination at the defect centre produces a distinctive PL spectrum consisting of a strong zero phonon transition at 1137 98(5) meV together with a well defined local mode structure containing a series of sharp, high energy local mode phonon replicas. The chemical nature of the defect is considered and is believed to incorporate both beryllium and oxygen, the latter of which is present in significant quantities in as grown Czochralski (CZ) silicon. An examination of the vibromc sideband of the zero phonon line supports this suggestion. Uniaxial stress spectroscopy shows the defect to have a low symmetry configuration, found to be consistent with a rhombic I (C^) symmetry group. The application of a magnetic field reveals no Zeeman splitting, indicating that the bound exciton must consist of two spin 1 / 2 particles, this behaviour is consistent with a pseudo-donor model where the angular momentum of the bound hole is strongly quenched in the low symmetry axial field of the defect. Conventional isotope substitution experiments with beryllium are impossible, as there is only one isotope of stable Be available. The use of radioactive isotopes is considered as a means of overcoming this problem. A feasibility study involving silicon implanted with radioactive indium is presented. This is the first occasion in which the PL spectra of defects involving radioactive isotopes have observed.