Ion irradiation of a-SiC:H produces strong reduction of the visible room temperature luminescence detected at very low ion fluence, typically 10(14) ions/cm(2) for a 150 keV H ion beam. Thermal annealing ill the range 200-500 degrees C is able to restore and/or enhance the original luminescence yield. Defects evolution induced by ion irradiation has been detected by Photothermal Deflection Spectroscopy (PDS) through their absorption in the sub-gap region and an increase up to a factor four has been observed in quenched materials. Analysis of the data with existing recombination models gives important insight on the recombination process itself through the determination of a characteristic carrier-defect average distance. Also. insight into the possible microscopic structure of the material has been inferred, After a cycle of ion irradiation and annealing. the stability of the luminescence under illumination is also increased, These facts point to possible increased performances of a-SiC:H based optoelectronic devices. (C) 1999 Published by Elsevier Science B.V. All rights reserved.