I'm trying to understand the concept of "self-trapped" and "charge-transfer" excitons, and I'm hoping someone can break these concepts down for me. I've studied Wannier and Frenkel excitons a bit. I'm reasonably unfamiliar with the concept of "self-trapping". I only know that it involves some deformation of the lattice, which isn't a very complete or understandable description. I don't really understand the idea of self-trapped electrons or holes, much less excitons. I also need to understand "charge-transfer" excitons in the context of inorganic semiconductors. I'm guessing this is more applicable with semiconductors with at least some degree of ionic character. This is particularly confusing to me, as I understood excitons to transfer energy with no net charge.