Preparation and Properties of Fluorescent Orthodontic Adhesives Containing Y₂O₃:Eu³⁺ Particles

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Orthodontic adhesives are typically colorless and transparent for aesthetic purposes. The utilization of fluorescence is one of the most effective solutions to make the adhesives visible for safe and complete removal after orthodontic treatments. Eu³⁺ ions were doped into yttrium oxides (Y₂O₃) using a homogeneous precipitation method. The crystals synthesized in this study exhibited submicron sizes and a very narrow size distribution. The X-ray diffraction (XRD) patterns agreed well with the known diffraction patterns of Y₂O₃, and indicated an absence of any other crystalline substances. Therefore, it was determined that the crystals synthesized in this study were in fact Y₂O₃:Eu³⁺. The spectra of the poly(methyl methacrylate) (PMMA) adhesives containing Y₂O₃:Eu³⁺ particles exhibited characteristic excitation and emission peaks corresponding to the 4f-4f transitions of Eu³⁺, despite the photoluminescence intensity being relatively low. The yielding loads of the Y₂O₃:Eu³⁺ particles contained in the PMMA specimens did not deteriorate by a significant amount. We conclude that it is feasible to add the Eu³⁺-doped Y₂O₃ crystalline particles into orthodontic adhesives.