This work analyzes the photoluminescence emission of Yb3+ and Tb3+ ions in co-doped silicon oxycarbide thin films, their activation by thermal treatment, and reveals their luminescent properties regarding the energy transfer between them. Three samples of silicon oxycarbide were prepared by rf magnetron sputtering from SiC, Yb and Tb targets in an oxygen/argon atmosphere. The first one is the undoped silicon oxycarbide sample, the second one is Tb single doped, and the last one is the Yb-Tb co-doped sample. All three samples are identified as silicon oxycarbides with a low carbon content using energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The latter shows the presence of the vibrational modes of Si–C and Si–O bonds. Subsequent annealing treatments up to temperatures of 750 °C led to the rare earths optical activation in the samples. For each annealing step, we present the photoluminescence spectra using an above-bandgap excitation of 325 nm. The Tb3+ and Yb3+ -related luminescence lines were identified. The Yb3+ ions luminescence for the co-doped sample shows concentration quenching above annealing temperatures of 500 °C whereas the Tb3+ ions luminescence intensity remains almost constant. The analysis of the photoluminescence excitation spectra shows the direct excitation of the Tb3+ ions in the Tb-doped samples. A high suppression of the direct excitation of the Tb3+ ions in the Yb-Tb co-doped samples was observed. The energy transfer from Tb3+ to Yb3+ ions in co-doped samples is evidenced, first, by the decrease of the Tb3+ photoluminescence intensity in the co-doped compared to the Tb doped sample. Second, a change from nearly single exponential to nonexponential decay in the Tb3+ photoluminescence decay curves and third, by the reduction of the Tb3+ decay time from 1.2 ms in the Tb-doped sample to 0.5 ms in the Yb-Tb co-doped sample. © 2019