Amorphous wide bandgap semiconductor thin films of the pseudobinary compound (SiC)1-x(AlN)x doped with terbium were grown by trial rf magnetron sputtering on CaF2 and glass substrates. The optical bandgap of the films in dependence of the composition x has been determined from transmission measurements using the (αhν)2 versus energy plot and the Tauc-plot. The bandgap varies from 2.2 eV for x = 0 (SiC) to 4.7 eV for x = 0.94 (almost pure AlN) and can be described by Vegard's law using the bowing parameter (3.18 ± 1.01) eV. Cathodoluminescence measurements show the typical terbium emission pattern. Thermal activation of the thin films with isochronical annealing from 300 °C to 1150 °C leads to strong increase of the emission with an optimal annealing temperature of 1100 °C. © 2010 Elsevier B.V. All rights reserved.