Abstract
The radiative-excited-state dynamics in crystals slabs is studied as a function of the slab thickness L. A general dispersion relation is derived that interpolates between the superradiant-exciton regime at thicknesses small compared to an optical wavelength λ and bulk polaritons and thick crystals. It is shown that previous results predicting superradiance in thick slabs (L≫λ) arise from invalid pole approximations.