The silicon 'dangling bond' defect plays a large part in controlling the electronic properties of a-Si, polycrystalline silicon, and the Si/SiO//2 interface. Jackson et al. have suggested that transitions of electrons occupying this defect produce the Urbach-like sub-gap absorption tail seen in two of these materials. We have peformed optical and electron spin resonance measurements on polycrystalline silicon, plastically deformed silicon, and Si/SiO//2 interfaces to examine this contention. In addition to seeing no measurable absorptance due to dangling bond interface states in the latter system, we conclude from the poor correlation of ESR signals with optical data that the Urbach tail in polycrystalline and deformed silicon is not due to transitions of dangling bond electrons.