The optical absorption spectra of metal iodides with layer structures

Abstract

The intrinsic optical absorption spectra of thin crystalline films of CaI 2, CdI 2, FeI 2, MnI 2, PbI 2, ZnI 2, BiI 3 and SbI 3 have been measured in the energy range 14,000–55,000 cm −1(1.7–6.8 eV). Sharp exciton peaks have been observed in the spectra of all these iodides, both near the intrinsic absorption edge and at much higher energies. The multiplicity and positions of the exciton peaks in most of these materials are consistent with a zero order model for the absorption process, which involves the excitation of iodide ions situated in the strong electric field which exists in iodide crystals with layer structures. This model predicts four strong exeiton peaks —a low energy halogen doublet occurring near the intrinsic absorption edge and a high energy halogen doublet one to two eV above the edge.