Urbach rule in the optical spectra of crystalline and amorphous organic-solids

摘要: Abstract In this paper we explore the effects of microscopic structural disorder on low energy optical absorption edges in some crystalline and amorphous organic solids. We advance a theoretical model which incorporates simultaneous static exciton—phonon coupling Frenkel exciton states. Explicit expressions were derived for self lineshapes by introduction two-step effective-field approximation, defining an effective hamiltonian was subsequently utilized within framework single site average t-matrix approximation scattering. Numerical results over broad temperature range demonstrate that scattering field Urbach type tails, where slope is independent.