Elucidating the Mechanism behind the Enhancement of Persistent Luminescence in ZnGa ₂ O ₄ : Cr ³⁺ Nanoparticles upon H ₂ O ₂ Exposure

ABSTRACT Persistent luminescence (PersL) materials exhibit prolonged emission of light, lasting from seconds to hours after stopping the excitation. At the nanoscale, they have attracted considerable interest for applications in in vivo imaging, photodynamic therapy, and biosensing. In 2023, an unexpected phenomenon was reported: a dose‐dependent enhancement of PersL in ZnGa 2 O 4 :Cr 3+ nanoparticles (ZGO:Cr 3+ NPs) upon exposure to hydrogen peroxide (H 2 O 2 ), opening a novel in vitro strategy for biomolecule detection. This strategy allows for fast and sensitive qualitative and quantitative detection of H 2 O 2 that is of major diagnostic relevance as it results from enzymatic processes and serves as a key biomarker in a wide range of diseases. This study investigates the fundamental mechanism underlying H 2 O 2 ‐induced PersL enhancement in ZGO:Cr 3+ NPs using a combination of structural, optical, photochemical, and surface chemistry analyses. It is demonstrated that under UV‐C irradiation, ZGO:Cr 3+ NPs produce photoelectrons initiating a redox reaction with adsorbed H 2 O 2 . Produced hydroxyl radicals ( • OH) interact with the nanoparticle surface to generate additional charge carriers, ultimately intensifying and prolonging Cr 3+ luminescence. These results reveal a previously unknown charging pathway in persistent phosphors, combining photocatalysis and chemiluminescence, and lay the foundations for advanced applications in biodetection and other emerging photonics technologies.