The absorption spectrum and excitons in an Ag2CdI4 ionic conductor

The electron absorption spectrum of thin stochiometric Ag₂CdI₄ films produced by thermal vacuum deposition on a quartz substrate in is investigated. The spectrum shape is sensitive to the method of preparation (the substrate temperature and deposition rate). Under optimal preparation conditions, the films are free of AgI and CdI₂ impurities and the fundamental absorption edge is at 3.28 eV. The long-wavelength exciton A band at 3.31 eV (90 K) is associated with the excitation of excitons in the AgI sublattice of the compound. An investigation of the temperature dependence of the spectral position and half-width of the A band in the range 90–430 K revealed that the exciton-phonon interaction makes the major contribution to the broadening of the band at T ≤360 K. At higher temperatures, the contribution associated with the generation of Frenkel defects with activation energy U _F=0.200±0.025 eV appears.