To make orthodontic adhesives visible as needed is valuable for safer and complete removal of them after orthodontic treatments. An attempt was made on doping trivalent europium ions into lattices of zinc oxides to make orthodontic adhesives visible by irradiation with purple or near ultraviolet light. The primary crystals of the synthesized products exhibited various sizes. However, overall, their diameters were on the nanoscale. The XRD patterns of them were in good agreement with those of hexagonal ZnO. However, the patterns also indicated the existence of another crystal-line substance that could be indexed as Eu2
. These results lead to the conclusion that ZnO:Eu3+
nanoparticles were suitably synthesized via a homogeneous precipitation method. As for the polymer adhesives containing the ZnO:Eu3+
nanoparticles, the photoluminescent spectra exhibited characteristic excitation and emission peaks corresponding to the intrinsic intra-4f transitions of Eu3+
. In addition, the yielding loads of the composite specimens did not deteriorate, regardless of the concentration of the ZnO:Eu3+
nanoparticles within the proportion of 1-3 wt%. The results obtained in this study suggest that the introduction of Eu3+
-doped ZnO nanoparticles into orthodontic adhesives is feasible.
Key words: fluorescence, photoluminescence, europium, zinc oxide, orthodontic adhesive