Direct
Observation of 4f Intrashell Excitation in
Luminescent Eu Complexes by Time-Resolved X‑ray Absorption
Near Edge Spectroscopy
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Abstract
We report time-resolved X-ray absorption
near edge structure (TR-XANES)
measurements at the Eu <i>L</i><sub>3</sub> edge upon photoexcitation
of several Eu<sup>III</sup>-based luminescent lanthanide complexes.
We find an unambiguous signature of the 4f intrashell excitation that
occurs upon energy transfer from the photoactive organic antennas
to the lanthanide species. Phenomenologically, this observation provides
the basis for direct investigation of a crucial step in the energy
transfer pathways that lead to sensitized luminescence in lanthanide-based
dyes. Interestingly, the details of the TR-XANES feature suggest that
the degree of 4f–5d hybridization may itself vary depending
on the excited state of the Eu<sup>III</sup> ion