An Evaluation of Fluorescent Orthodontic Adhesives Containing Eu-doped ZnO at Room Temperature

Abstract

Making orthodontic adhesives visible is important for their safer and complete removal after orthodontic treatments. In this paper, we report our research on doping trivalent europium ions into lattices of zinc oxides to make orthodontic adhesives visible under purple or near ultraviolet light irradiation. The primary crystals of the synthesized products were on the nanoscale, although their size and crystallinity varied with the annealing temperatures. The X-ray diffraction (XRD) patterns were in good agreement with that of hexagonal wurtzite ZnO with the exception of patterns acquired from the products obtained by annealing at 200°C. However, with regard to the photoluminescence, the polymer adhesives containing ZnO:Eu³⁺ particles indicated characteristic excitation and emission peaks corresponding to the intra-4f transitions of Eu³⁺, although these peaks were not intense and sharp. We think that the phonon resonance can be considered as the most acceptable cause for the insufficient photoluminescence observed in this study bearing in mind that the phonon resonance is originated from the Zn interstitials. At the current moment, we conclude that the nanocrystalline ZnO could have numerous defects. By controlling the formation of defects during synthesis, we believe that the ZnO:Eu³⁺ nanocrystals will become much more useful toward developing new fluorescent orthodontic adhesives.