Reduction mechanism and energy transfer between Eu³⁺ and Eu²⁺ in Eu-doped materials synthesized in air atmosphere

This article critically examines the reduction mechanisms and energy transfer processes between trivalent europium ions (Eu³⁺) and divalent europium ions (Eu²⁺) in materials synthesized in an air atmosphere. It also encompasses various materials and conditions, including a critical analysis of the reduction mechanism and energy transfer between Eu³⁺ and Eu²⁺ in Eu-doped materials. Specific investigations include exploring the reduction process in BaMgSiO₄:Eu, focusing on factors influencing the reaction. The article also covers low-temperature self-reduction, addressing conditions and mechanisms such as the charge compensation model and laser-induced reduction. Additionally, it explores the influence of charge compensation on luminescent properties, emphasizing enhancements in red emission. Investigations into the role of oxygen vacancies in the reduction of Eu³⁺ and their implications on material properties are presented. This article further digs into abnormal reduction processes and the formation of defect centers in Eu³⁺-doped pollucite, proposing a substitution defect model for the self-reduction of europium ions in silicate Ba(Eu)MgSiO₄ phosphors. Unusual reduction phenomena, such as reduction via boiling water in Yb₂Si₂O₇:Eu³⁺ phosphors, and reductions in various glass systems, including porous glass, ZnO-B₂O₃-P₂O₅ glasses, aluminoborosilicate glasses, europium-doped Li₂B₄O₇ glass, and aluminosilicate oxyfluoride glass (AOG), are also thoroughly examined.