Photoemission spectroscopy of layered halides: PbI2and BiI3

The valence bands of Pb${\mathrm{I}}_2$ and Bi${\mathrm{I}}_3$ have been studied by means of uv synchrotron-radiation photoemission spectroscopy and x-ray photoemission spectroscopy. High-resolution data, taken for different photon polarizations and various photon energies, show several new features. In particular, new pronounced structures have been found 0.8 and 1.0 eV below the top of the valence bands for Pb${\mathrm{I}}_2$ and Bi${\mathrm{I}}_3$, respectively. These structures are believed to correspond to the theoretically predicted, split-off $\mathrm{Pb}\mathrm{}\left(6s\right)\mathrm{}-\mathrm{I}\mathrm{}\left(5p\right)\mathrm{}$ hybrids. While there is not quantitative agreement between theory and experiment, these new results present strong experimental evidence for the anomalous hybridization effects of essentially nonbonding cation $s$ electrons in semiconducting layered halides.