Synopsis
Subsequent to the orthodontic treatment, removal of residual colorless adhesives from tooth surfaces by cutting instruments with the lowest possible iatrogenic damage has been a long-standing challenge. Fluorescent imaging can be one of the most effective solutions. Y₂O₃:Eu³⁺ particles were synthesized by a homogeneous precipitation method and the subsequent calcination was performed at various temperatures. The particles had a narrow size distribution (200-300 nm) and showed sharp crystallinity independent of the calcination temperatures above 800°C. In this study, 1,000°C is confirmed to be the optimum calcination temperature. Although the reason for the decline in emission intensity of the 1,100°C-calcined particles is still unclear, loss of spherical shape associated with excessive crystal grain growth and simultaneous sintering to each other by firing is a possible explanation. The emission from the phosphor-containing resins, intended for use in orthodontic adhesives, is appreciable although the emission intensity of the resins was weak even if their content was 20 wt.%. The decrease in emission intensity may be attributed to the scattering by the particles or cross relaxation processes. We conclude that the crystalline Y₂O₃:Eu³⁺ particles calcined at 1,000°C could be applicable for further development of photoluminescent orthodontic adhesives.

Key words: fluorescence, calcination, orthodontic adhesives, europium, yttrium oxide

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