Exciton absorption spectrum of M3Cu2I5 (M = Cs, Rb) thin films

The absorption spectra of Cs3Cu2I5 and Rb3Cu2I5 thin films were studied in the spectral range of 2–6 eV and the temperature range of 90–290 K. Analysis of the spectra revealed that small-radius excitons are excited in Cs3Cu2I5 and Rb3Cu2I5 compounds. The influence of exciton-phonon interaction on the parameters of the exciton bands in Cs3Cu2I5 and Rb3Cu2I5 thin films was investigated. The two-dimensional nature of excitons in Cs3Cu2I5 and Rb3Cu2I5 was established based on the temperature dependence of the half-width of long-wave exciton bands.