Photoluminescence fatigue in amorphous carbon (a-C) films prepared by d.c. magnetron sputtering

We have studied the fatigue effect in unhydrogenated amorphous carbon ( a -C) films prepared by d.c. magnetron sputtering of graphite. At 12 K the fatifued photoluminescence spectra show neither a spectral shape change nor peak shift during illumination. The fatigued photoluminescence intensity at a fixed energy shows a t − b time process during illumination. The self-recovery of the fatigued photoluminescence in the dark requires much more time than hydrogenated amorphous silicon ( a -Si : H) and less than amorphous phosphorus ( a -P). The light induced defects in a -C films are in metastable states and explained to be π defects rather than dangling bonds (σ defects) as in a -Si : H or hydrogenated amorphous carbon ( a -C : H).