# Electronic and Structural Relaxation of Photoexcited WO3 Observed by Femtosecond Resonant X‑ray Emission Spectra

## TL;DR

This study uses advanced X-ray techniques to observe how tungsten trioxide reacts to light on ultrafast timescales, revealing changes in its electronic and structural properties.

## Contribution

The paper introduces the use of HERFD-XAS and RXES to study femtosecond dynamics in 5d transition metal oxides.

## Key findings

- Photoexcitation causes a shift in the W L3 edge XAS and modulates energy levels of t2g and eg peaks.
- Local structural changes around W atoms are observed within 500 fs due to polaron formation.
- HERFD-XAS and RXES provide detailed insights into the early photoexcited states of WO3.

## Abstract

Photoexcited states
of tungsten trioxide (WO3) were
observed using femtosecond high-energy-resolution fluorescence detection
X-ray Absorption Spectra (HERFD-XAS) and resonant X-ray emission spectra
(RXES). In the initial state of the photoexcitation (∼100 fs),
the W L3 edge XAS shifts to lower energy and the energy
levels of the t
2g and e
g peaks are modulated due to the photoexcited electrons
in the conduction band. The electronic state of the photoexcited W
atoms is modified by 500 fs. The crystal field splitting between
the t
2g and e
g peaks shrinks by 500 fs, which indicates local structural changes
around the W atoms due to the formation of polarons. HERFD-XAS and
RXES provide more details about the early state of the photoexcited
states of WO3. This work demonstrates that the detailed
dynamics of 5d elements in the femtosecond range can be addressed
with HERFD-XAS/RXES.