We have performed photo- and electroluminescence measurements on erbium doped silicon and SiGe samples containing different amounts of germanium. All samples were grown completely by molecular beam epitaxy. Oxygen was used as a codopant to enhance the luminescence efficiency. The photoluminescence data show a systematic variation of the thermal activation energy obtained from temperature dependent intensity measurements with varying germanium contents. For samples with an alternating Si/SiGe layer structure stronger photoluminescence is observed when the erbium ions are incorporated into the SiGe layers rather than into the silicon layers. We attribute this to the capture of photogenerated carriers in the SiGe layers. Electroluminescence from erbium doped SiGe samples which have been processed as diodes has been observed up to room temperature in both surface and edge emitting geometries.