The fundamental optical absorption spectra of CsPbI3 and Cs4PbI6 have been measured for the first time. There are distinct differences in the absorption characteristic between the two compounds: Cs4PbI6 exhibits strong, oscillator-like absorption and a prominent, blue-shifted excitonic peak, compared to the case of CsPbI3. The differences are explainable in terms of whether the Pb2+(I-)(6) octahedra are weakly (CsPbI3) or strongly (Cs4PbI6) mutually isolated in the respective compounds. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 17]
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