Abstract
Field-induced changes of the lattice potential modify bandstates and discrete electronic states and their response to light, which is resolved by field-modulated spectroscopy. Very different spectral lineshape is observed for discrete exciton states in different types of solids with extended electronic states: bulk and superlattice semiconductors, ~ -conjugated polymers and molecular solids consisting of weakly interacting large organic molecules with conjugated ~ -electrons. Spectral lineshape and size of the effects depend on the relative strength of the field-induced potential to the Coulomb potential or other boundary conditions.