Defect-driven photoluminescence quenching in WO3 micro-flakes: a simple approach for bisphenol A detection

Abstract

Accurate and simple detection of environmentally hazardous molecules such as bisphenol A (BPA) remains a significant challenge in optical sensing. This study presents a novel approach utilizing photoluminescence (PL) spectroscopy of tungsten trioxide (WO₃) micro-flakes synthesized via a solution-phase route, with enhanced sensitivity achieved through controlled annealing. The annealing process at 350 °C under low vacuum induces a phase transition from orthorhombic to monoclinic structure and increases oxygen vacancy concentrations, which are direction dependent within the crystal lattice. These vacancies act as emission centers, whose PL response is modulated by BPA concentrations, resulting in measurable quenching effects. Theoretical predictions of charge transition levels (CTLs) identify the key emission centers responsible for the observed optical behavior. The method achieves a detection limit of 0.025 μmol/L, demonstrating sensitivity comparable to other complex analytical techniques, while offering advantages in simplicity and real-time monitoring. The underlying quenching mechanism involves electron transfer from oxygen vacancies to BPA’s H⁺ ions, confirming a static quenching pathway. The present work primarily demonstrates the feasibility of defect-engineered WO₃ as a model optical transducer for BPA through a vacancy-mediated quenching mechanism, that can serve as a foundation for future selectivity and real-sample studies. This work advances optical sensing by coupling crystal structure engineering with PL spectroscopy, providing an efficient and practical platform for environmental and health monitoring of biohazardous molecules.