If my understanding is correct, quantum dots are tiny crystals where the confined electronic degrees of freedom have discrete energy levels. In this paper Phys. Rev. B 65, 195313 (2002), and many others, electron-phonon coupling is discussed in the context of quantum dots. I understand what is meant by a phonon in the context of macroscopic crystals, but what is the meaning of a "phonon in a quantum dot".
I am guessing, but not sure, that since a quantum dot is a tiny crystal we can also define phonon as excitation of the lattice degrees of freedom, with the difference that their energy will be discrete due to confinement.
