Competing Self-Trapped Exciton States and Multiple Emission Pathways in BiVO₄

Area of Science:

• Materials Science
• Photochemistry
• Computational Chemistry

Background:

• Bismuth vanadate (BiVO₄) is a promising material for photoelectrochemical water-splitting.
• Charge localization, particularly small polarons, affects BiVO₄ performance.
• The nature of experimentally observed self-trapped excitons (STEs) in BiVO₄ is not fully understood.

Purpose of the Study:

• To elucidate the localization, stability, and optical properties of STEs in BiVO₄.
• To provide a theoretical explanation for the observed emission spectra of BiVO₄.
• To advance the understanding of charge carrier dynamics in transition metal oxides for photocatalysis.

Main Methods:

• Time-dependent density functional theory (TD-DFT) calculations were performed.
• A nonempirical PBE0(α) hybrid functional was utilized for accurate electronic structure.
• Calculations focused on exciton configurations, energies, and optical spectra.

Main Results:

• Two distinct, energetically similar STE configurations were identified in BiVO₄.
• Simulated emission spectra from a single STE configuration show multiple peaks.
• Calculated optical spectra align well with experimental observations.

Conclusions:

• The study clarifies the nature of STEs in BiVO₄, identifying two stable configurations.
• The findings explain the complex emission spectra through internal transitions within STEs.
• This work enhances the fundamental understanding of BiVO₄ for efficient photocatalytic water-splitting.