The effect of the annealing temperature on the light emission intensity of Tb-doped a-SiC:H thin films was investigated for different Tb concentrations under sub-bandgap photon excitation. We present a detailed discussion of rare-earth thermal activation in order to determine the optimal Tb concentration and annealing temperature for the highest Tb-related light emission intensity. Two independent processes that enhance the emission intensity are identified and incorporated in a rate equation. These are the thermally-induced increase of luminescence centers and the inhibition of host-mediated non-radiative recombinations. Finally, the presented analysis revealed a suppression of the self-quenching effect when increasing the annealing temperature.