UV absorption spectra of thin films of Cs2CdI4 and Rb2CdI4 ferroelectrics

Thin films of M2CdI4 ferroelectrics (M=Cs, Rb) of orthorhombic structure were synthesized, and their electronic optical spectrum was studied. It was established that both compounds belong to direct-gap dielectrics and that their low-frequency excitons are localized on a sublattice made up of (CdI4)(2-) tetrahedra. The temperature dependence of the exciton band parameters was studied for Cs2CdI4 within the temperature interval 90-420 K. The phase transitions occurring in this interval manifest themselves as breaks in the temperature behavior of the band spectral positions and weak peaks in the halfwidth and oscillator strength. (C) 2003 MAIK "Nauka/Interperiodica".