Size dependence of exciton–light interaction in a spherical semiconductor from quantum dot to bulk limit

Exciton–light coupled modes in a spherical crystal are studied as a function of radius. The coupled mode has complex eigenenergy, and its imaginary part corresponds to the radiative width in optical spectra. The radiative width of each mode shows resonant enhancement as a function of crystal size due to the cavity effect. The maximum radiative width increases with radius, and it seems to be inconsistent with the fact that the coupled mode becomes a polariton in a bulk limit. We discuss graphically and qualitatively how coupled mode approaches polariton state.