Optical Spectra and Excitons in Ternary Cs2AgI3 and CsAg2I3 Compounds

摘要

Optical spectra of thin films of ternary Cs2AgI3 and CsAg2I3 compounds are investigated in the 36-eV-spectral range at 80 and 290 K. It is shown that low-frequency electronic excitations and excitons are related to the AgI sublattice. The binding energy of excitons and the forbidden bandwidth are found to be Rex=0.415 and 0.265 eV and Eg = 4.845 and 3.99 eV in Cs2AgI3 and CsAg2I3, respectively. Comparison of the absorption spectra of -AgI, CsAg2I3, and Cs2AgI3 suggests a quasi-one-dimensional nature of the electronic bands in ternary compounds. It is shown that the complex shape of the optical spectrum of CsAg2I3 is related to the existence in this compound of double chains consisting of the AgI4 tetrahedra.