Abstract Electron spin resonance (ESR) and photoluminescence (PL) measurements have been employed to investigate some electronically important defects in nitrogen-rich amorphous silicon nitride films (a-SiN x :H where x > 1.3) prepared using plasma-enhanced chemical vapor deposition. The PL intensity decreases with time (fatigues) when excited with UV light. This fatigued PL can be restored (bleached) with the application of visible light. There exists an ESR signal in as-deposited films of a-SiN x :H which is temperature dependent. This ESR signal can be increased by irradiation with UV light, and the increased ESR signal can be bleached by application of visible light. Microscopic models for the defects responsible for these effects are discussed.