optics - Optical absorption -- what are the common ranges and mechanisms?

So let's say you do some reflection/transmission spectroscopy of a material. It's clear that it's absorbing in some range.

What would be your first step in identifying the source of the absorption? The two main clues I would look at would be

1. The range it occurs in (if your incident light is in the x-ray range, it's clearly not phonon absorption, for example)


2. The shape of the absorption (is it a peak? Or an absorption 'edge', where it isn't absorbing below some energy, and absorbs everything above, for example)

But I'd like to know if there are other ways as well.

Additionally, does anyone know of a 'map' of the ranges you'll typically find different types of absorption in? I saw one on wikipedia once, but it only had three types, and now I can't find it of course. For example, a few types of absorption I can think of off the top of my head are

• Interband electron transitions


• Intersubband electron transitions


• Impurities


• Phonons



• Vibrational modes


• Atomic transitions

I understand that a lot of these will be material-dependent, but often the same mechanism in different materials will yield absorption in the same order of magnitude range. What ranges would one typically see these (and other) absorption mechanisms in?

Thank you!