Absorption spectra of thin layers of solid solutions Cs2(Cd1 − xZnx)I4

The excitonic absorption spectra of thin films of ferroelectric Cs2CdI4 and Cs2ZnI4 solid solutions are studied for the first time. It is found that, within the whole range of molar concentrations x, the spectra of Cs2(Cd1 − xZnx)I4 comprise two bands that originate from the bands of the two compounds. It is shown that the exciton transfer occurs most efficiently between the tetrahedrons CdI4 and ZnI4 along the b axis of the crystal. Unusual behavior of the concentration with regards to the maxima of long-wavelength excitonic bands Em(x) agrees well with the developed theory that takes into account dependence on x of the matrix element of the intertetrahedron exciton transfer and that is similar to the theory of Davydov’s splitting in molecular crystals.