The electronic structure of In 4 Sn 3 O 12 has been studied by optical and x-ray photoemission spectroscopies and has been compared to electronic structure calculations carried out using density-functional theory. An excellent agreement is found between the experimental valence-band structure and that predicted by the calculations. The valence band derives its dominant character from O 2p states with three distinct features emerging from the hybridization with In and Sn 5s, 5p, and 4d states,

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... spectively. The position of the valence-band edge in the x-ray photoemission spectrum suggests a fundamental electronic gap of 2.7 eV whereas the onset of strong optical absorption is predicted to occur at 3.3 eV.