Ultrafast light-induced formation of a metastable hidden state in bismuth vanadate

TL;DR

This study reveals ultrafast formation of a metastable hidden state in bismuth vanadate driven by light, involving rapid electron localization and slower lattice reorganization, with implications for solar fuel applications.

Contribution

It uncovers the dynamics of photoinduced states in BiVO$_4$, combining femtosecond spectroscopy and DFT to identify a novel hidden structural state stabilized by hole-lattice interactions.

Findings

Sub-picosecond electron localization within VO$_4$ tetrahedra.

Multi-picosecond lattice reorganization into a hidden state.

The hidden state is structurally distinct from known phases.

Abstract

Bismuth vanadate (BiVO$_4$) is a key photocatalyst for solar fuel applications, yet fundamental questions remain regarding the nature of photogenerated polaronic states and the lattice dynamics that govern its light-to-chemical pathways. Here, we use femtosecond optical pump-X-ray probe measurements to track the photoinduced electronic and structural dynamics in BiVO$_4$ across multiple length and time scales. Transient X-ray absorption spectroscopy captures sub-picosecond electron localization within VO$_4$ tetrahedra, consistent with small polaron formation, whereas time-resolved X-ray diffraction reveals a slower, multi-picosecond lattice reorganization into a hidden photoexcited state that is structurally distinct from both the monoclinic ground state and the high-temperature tetragonal phase. Supported by density functional theory, we show that hole-lattice interactions dynamically reduce the ground state monoclinic distortion, stabilizing the hidden state. Our results demonstrate that electron- and hole-lattice coupling jointly shape the excited state landscape, with implications for carrier transport, interfacial energetics, and light-to-chemical energy conversion pathways.