Polaron and Exciton-Phonon Complexes in CuCl Nanocrystals

We report the first evidence of an excitonic polaron and exciton-phonon complexes in nanosize semiconductor crystals. These are observed in CuCl nanocrystal excitonic luminescence spectra under resonant size-selective excitation. The theory of exciton coupling with spherical phonons through the Fröhlich and deformation potentials is developed and describes both the size dependence of the polaron binding energy and the degree of the exciton-phonon hybridization near resonance, when the $1P$ and $1S$ exciton level spacing coincides with the one- or two-phonon energy.