The fabrication of efficient silicon-based Light Emitting Devices (LEDs) is extremely important for the integration of photonic and electronic components on the same Si platform. In this paper, we report on the room temperature electroluminescence properties of Tb-doped MOS-LED devices with an active layer of SiO2 and Si-rich SiOx produced using the magnetron co-sputtering technique. The electroluminescence properties of both types of devices were studied as a function of processing conditions and material properties. A clear Tb3+ electroluminescence signal from the D-5(4)-> F-7(j) transitions has been observed without any parasitic defect emissions from the active layer hosting the Tb3+ ions. We have shown that the incorporation of excess Si into the active layer significantly enhances the electroluminescence signal, which lowers the turn on voltage below 10 V and is crucially important for meeting the low-power requirements for integrated circuit applications. We also addressed some of the fundamental questions concerning the light generation mechanisms in the Tb-doped system. (C) 2012 Elsevier B.V. All rights reserved.