European XFEL Seminar

Dynamics of photo-induced charge excitations in functional oxides

by Paola Luches (Nanoscience Institute, CNR, Modena, Italy)




Oxide-based materials find wide application as stable and non-critical compounds for solar to chemical/electric energy conversion. A detailed understanding of the dynamics of light-induced excited states is indeed very relevant for the optimization of the photochemical and photoelectric functionalities.

Starting from the case of cerium oxide based systems, also in combination with plasmonic nanoparticles, I will show how ultrafast spectroscopies have allowed to unravel relevant aspects of the excited states dynamics. In particular, femtosecond transient absorption studies [1,2] have provided a solid basis for subsequent pump-probe X-ray absorption spectroscopy studies at the FERMI free-electron laser [3]. The results have allowed to demonstrate the formation of a small-polaron state after band-gap excitation, with influence on the transport properties and on the reducibility of the material [2]. The excitation of localized surface plasmon resonances in Ag and Au nanoparticles, embedded in cerium oxide matrices, has been shown to decay via an efficient and stable charge/energy transfer to the surrounding metal oxide [1,3]. The process has been demonstrated to induce an ultrafast (t < 200 fs) modification of the shape of the Ce N45 absorption edge, compatible with a charge transfer from the resonantly excited plasmonic nanoparticles to the empty Ce 4f levels [3]. The possibility of accessing the dynamics at shorter times and of using more sensitive detection methods is very promising to obtain an even better insight into the specific complex processes, which come into play after photoexcitation in this class of materials.

[1] J. S. Pelli Cresi et al., Nanoscale 11, 10282 (2019).

[2] J. S. Pelli Cresi et al., J. Phys. Chem. Lett., 11, 5686 (2020).

[3] J. S. Pelli Cresi et al., Nano Letters 21, 1729 (2021).


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Organized by

Sakura Pascarelli / Gabriella Mulá-Mathews