Impact of X-Ray Irradiation on the Bi Valence of MA₃Bi₂I₉ and Cs₃Bi₂I₉

Abstract

We have investigated the electronic structure and the X-ray radiation effect in MA3Bi2I9 and Cs3Bi2I9. X-ray photoemission spectroscopy of MA3Bi2I9 films indicates that Bi5+ species are produced as a result of the destruction of MA+ molecules by X-ray irradiation. The valence control by X-ray radiation in the Bi halide is a unique feature that can serve as a new playground to study the physics and chemistry of the Bi3+/Bi5+ mixed valence state. On the other hand, the Bi3+ states of Cs3Bi2I9 films are robust against X-ray irradiation, suggesting that Cs3Bi2I9 is a more suitable material than MA3Bi2I9 as a photo-absorber or X-ray detector material for use in space.