Optical Constants and Excitons of Alkali Cuprous Halide Crystals

The anisotropic reflection spectra of K₂AgI₃ Rb₂AgI₃ and Rb₂AgBr₃ have been measured in the range from 4 to 26 eV using synchrotron radiation. The optical constants have been obtained through the Kramers-Kronig analysis. The characters of the band edge excitons of K₂AgI₃ and Rb₂AgI₃ are very similar to those of the alkali iodides. However, the perturbation calculation has indicated that the spin-orbit interaction scarcely affect the outline of the valence band structure of Rb₂AgI₃ and that no spin-orbit doublet appears in the absorption spectra. The anisotropic absorption due to the core excitons of K⁺ or Rb⁺ have been found around 20 or 17 eV, respectively. The prominent structures due to plasmons of valence electrons have been found at 10-12 eV in the energy loss spectra.