I'm having a tough time finding a good reference for excitons. I know next to nothing about them, and I'd like to find a good book/paper/notes that would introduce it in a slow, pedagogical way. Things like the how to compute their energies, wavefunctions, the Bethe-Salpeter eqautionequation and I guess a lot more that I don't know but I should've. Do you know some? Thanks in advance!