Paramagnetic States in Oxygen-Doped Boron Nitride Extend Light Harvesting and Photochemistry to the Deep Visible Region

A family of boron
nitride (BN)-based photocatalysts for solar fuel
syntheses have recently emerged. Studies have shown that oxygen doping,
leading to boron oxynitride (BNO), can extend light absorption to
the visible range. However, the fundamental question surrounding the
origin of enhanced light harvesting and the role of specific chemical
states of oxygen in BNO photochemistry remains unanswered. Here, using
an integrated experimental and first-principles-based computational
approach, we demonstrate that paramagnetic isolated OB3 states are paramount to inducing prominent red-shifted light absorption.
Conversely, we highlight the diamagnetic nature of O–B–O
states, which are shown to cause undesired larger band gaps and impaired
photochemistry. This study elucidates the importance of paramagnetism
in BNO semiconductors and provides fundamental insight into its photophysics.
The work herein paves the way for tailoring of its optoelectronic
and photochemical properties for solar fuel synthesis.