Ultrafast Formation of Small Polarons and the Optical Gap in CeO₂

Abstract

The 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 CeO 2 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 ( E og = 4 eV), significantly larger than usually reported.

Ultrafast Dynamics of Plasmon-Mediated Charge Transfer in Ag@CeO2 Studied by Free Electron Laser Time-Resolved X-ray Absorption Spectroscopy

“…The spectra, in Figure , show that the absorbance of the ceria film without Ag NPs exhibits a peak at 300 nm (blue line). This spectral feature is compatible with excitations from the valence band to empty 4f levels, in agreement with the literature. , The Ag@CeO 2 sample shows broad and intense absorbance peaks centered at 400 and 650 nm, ascribed to the LSPR excitation of Ag NPs. The specific origin of the two peaks was investigated through simulations of the absorbance of Ag NPs in a CeO 2 matrix, performed using the boundary element method, as implemented in the MNPBEM17 toolbox .…”

“…CeO 2 (cerium oxide or ceria) plays an important role as a TMO catalyst. Its electronic configuration, with a bandgap in the ultraviolet range (3.2–4.0 eV), , allows fast and reversible changes between the more stable 4+ oxidation state and the 3+ oxidation state of Ce with one extra electron localized in the Ce 4f levels between the filled valence band and the empty conduction band. This property is associated with the remarkable capability of ceria to store, transport, and release oxygen depending on the environmental conditions.…”

Photoexcited Ultrafast Dynamics of Free Carriers and Polarons in V2O5 Microparticles through Time-Resolved Nondegenerate Pump Probe Spectroscopy

“…(The variation of the formation time with the excitation density extracted from the occupation of N D and from the rate of formation R 1 is shown in Figure S11.) The estimated polaron formation time of ∼4.5 ps from our empirical polaron modeling seems larger by one order compared to ∼25–600 fs ,− in other TMOs. The longer polaron formation time may possibly be due to the relatively weak coupling between large wave-vector phonons and the electrons in V 2 O 5 and the exact implication of this observation requires further studies.…”

Atomistic insight into the formation dynamics of charged point defects: A classical molecular dynamics study ofF+-centers in NaCl

“…Thus, an atomistic understanding of the rearrangement dynamics associated with charge-state changes in point defects could significantly aid the design of energy materials [18,19]. Moreover, recent experimental advances in detecting lattice relaxation dynamics point to the need for furthering our atomic-scale understanding of such phenomena [15,[20][21][22][23][24][25][26][27]. Following this vein of inquiry, we explore atomistically the manner in which a newly formed charged defect center relaxes its excess energy through dissipation within a surrounding lattice.…”

“…An important long-term goal in the field is to understand atomistically the mechanisms through which defect centers dynamically interact with their surrounding lattice [36,37]. By successively improving our atomistic models of the lattice rearrangements induced by charge defect centers, via refined interaction descriptions, further quantitative comparison with experiments should be achievable [15,[20][21][22][23][24][25][26]. Such investigations would also serve to eventually reconcile both analytical and atomistic descriptions of charged defect centers and their lattice formation/excitation dynamics.…”