Bi₂O₃–Y₂O₃:Yb,Er Upconversion Phosphors for Efficient Photocatalytic Degradation of Congo Red and Pharmaceutical Mixtures

Abstract

Y₂O₃-Bi₂O₃:Yb³⁺,Er³⁺ mixed oxides were investigated as multifunctional materials for the removal of recalcitrant contaminants from water through solar photocatalysis. Congo red (CR) and a pharmaceutical mixture (CHL) containing ciprofloxacin, hydrocortisone, and lidocaine were used as model pollutants. The Y₂O₃/Bi₂O₃ molar ratio was varied (25/75, 50/50, and 75/25), producing the 25Y75BO, 50Y50BO, and 75Y25BO samples, respectively. Among them, 25Y75BO exhibited the best photocatalytic performance, achieving >95% degradation of both CR and CHL after only 20 min of solar irradiation. Increasing the Y₂O₃/Bi₂O₃ ratio decreased the photocatalytic efficiency, with CR degradation decreasing from 95% for 25Y75BO to 82% for 75Y25BO. Reusability tests showed that the photocatalytic activity decreased to approximately 75–80% after three cycles. However, thermal regeneration at 400 °C in air successfully restored the photocatalytic performance to >95% degradation within 20 min. Scavenger experiments revealed that photogenerated holes (h⁺) and hydroxyl radicals (•OH) are the main reactive species involved in contaminant degradation. The upconversion properties were also investigated under 980 nm excitation and correlated with photocatalytic activity. Green and red emissions were observed, while the emission color shifted from orange to yellow as the Y₂O₃/Bi₂O₃ ratio increased. Moreover, the integrated upconversion emission intensity decreased with increasing Y₂O₃ content, suggesting a composition-dependent relationship between optical and photocatalytic properties. Overall, Y₂O₃–Bi₂O₃:Yb³⁺,Er³⁺ mixed oxides, particularly 25Y75BO, exhibit high solar photocatalytic efficiency, good regenerability, and tunable upconversion emission, demonstrating their potential as multifunctional materials for environmental remediation and photonic applications.

Keywords: Photocatalysis; Upconversion Luminescence; Defect engineering