The effect of terbium (Tb) doping on the photoluminescence (PL) and cathodoluminescence (CL) spectra of amorphous aluminum nitride (a -AlN) and amorphous silicon nitride (a -SiN) thin films has been investigated for different temperature conditions. The samples were prepared by RF dual magnetron reactive sputtering technique with a Tb concentration of about ∼1 at% An enhancement of the light emission is obtained after thermal annealing treatments following the activation of luminescent centers. Furthermore, the Tb related integrated light emission intensity is reported exhibiting a continuous increase with the samples temperature well below thermal quenching for both materials. This behavior suggests a phonon assisted energy migration mechanism which contributes to the effective energy transfer from the matrix to the Tb ions.