Ion implantation and annealing have been used to switch the luminescence in Si1-xGex/Si quantum wells from a band-edge exciton process to a broad well below the band edge. The damage introduced by silicon ion implants, which leads to the formation of the platelets correlated with broad band luminescence, is related to the track of an implanted ion and the recoiled atoms in the quantum well structures. The activation energy for defect clusters is about 0.1eV, which is larger compared with the activation energy of ～0.05 eV for interstitial atoms. This indicates that the defect clusters is responsible for the deep broad photoluminescence in early MBE samples.