Donor bound exciton luminescence has been detected in silicon grown by molecule beam epitaxy at 550 degrees C and 750 degrees C with an intensity comparable with that observed in silicon grown from the melt with a similar electrically active donor concentration. Therefore, the strong suppression of luminescence from electrically active impurities reported in previous investigations is not an inherent property of MBE silicon grown at low temperatures and must be associated with the presence of other contaminants. The major inadvertent electrically active dopant is seen to be phosphorus in the material investigated. The relative strength of the bound exciton luminescence from the epitaxial layers and that arising in the substrate can be varied by heat treatment and deliberate contamination by transition metals. The latter treatment is also seen to result in the appearance of dislocation D-band luminescence which is not observed in the as-grown material, implying that D-band luminescence is associated with decorated as distinct from undecorated dislocations.