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Ultrafast Formation of Small Polarons and the Optical Gap in CeO2
journal contribution
posted on 2020-07-02, 19:07 authored by Jacopo Stefano Pelli Cresi, Lorenzo Di Mario, Daniele Catone, Faustino Martelli, Alessandra Paladini, Stefano Turchini, Sergio D’Addato, Paola Luches, Patrick O’KeeffeThe
ultrafast dynamics of excited states in cerium oxide are investigated
to access the early moments of polaron formation, which can influence
the photocatalytic functionality of the material. UV transient absorbance
spectra of photoexcited CeO2 exhibit a bleaching of the
band edge absorbance induced by the pump and a photoinduced absorbance
feature assigned to Ce 4f → Ce 5d transitions. A blue shift
of the spectral response of the photoinduced absorbance signal in
the first picosecond after the pump excitation is attributed to the
dynamical formation of small polarons with a characteristic time of
330 fs. A further important result of our work is that the combined
use of steady-state and ultrafast transient absorption allows us to
propose a revised value for the optical gap for ceria (Eog = 4 eV), significantly larger than usually reported.