Excitonic absorption spectrum of Rb2ZnI4 thin films

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The absorption spectrum of Rb2ZnI4 thin films in the spectral region 3–6eV is investigated in the temperature range 90–290K. It is found that the compound is a direct-gap insulator and that the low-frequency excitations are localized in the ZnI42− structural layers of the crystal lattice and are of a quasi-two-dimensional character. For T<200K the temperature dependence of the spectral absorption and the half-widths of the long-wavelength exciton band exhibits thermal memory effects due to precursors of the low-temperature phases.