Optical Spectra of Inorganic-Organic Compounds (C₂H₅NH₃)₂CdCl₄ in 3-30 eV Range

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Reflection spectra of (C₂H₅NH₃)₂CdCl₄ single crystals have been investigated in the range of 3-30 eV using synchrotron radiation. Two kinds of exciton bands with the splitting of the order of 0.1 eV, which is almost equal to the spin-orbit splitting of a Cl atom, are observed at 6.19 and 8.20 eV at 7 K. These bands are located at the energy positions close to the lowest exciton bands of CdCl₂ and C₂H₅NH₃Cl crystals, respectively. On rising the sample temperatures, the 8.20 eV band shows a discontinuous peak-shift of 0.1 eV around the temperature where a structural phase transition occurs, while such a result is not observed for the 6.19 eV band. The 6.19 eV band is assigned to the electronic transition from the Cl^- 3p valence band to the lower Cd²⁺ 5s conduction band, and the 8.20 eV band to that from the Cl^- 3p valence band to the upper NH₃^- s-like conduction band.