Pigments based on Er2O3-Al2O3: Preparation and colouring performance in zirconia ceramics

Abstract Two types of pigments, those with ErAlO3 and Er3Al5O12 as the main crystal phase, were synthesized by the gel-polymerization method. The colour performance of the pink pigments in zirconia ceramics was also studied. Field scanning electron microscopy combined with energy dispersion spectrometry, X-ray diffraction (XRD), UV–Vis–NIR absorption spectrometry, and colourimetry were applied for phase composition, microstructure and colour property analyses of pigments and pink ceramics. The experimental results showed that in the Er2O3-Al2O3 system, the Er3Al5O12 phase occurred at a lower temperature and the ErAlO3 phase appeared at a relatively higher temperature, accompanied by a small amount of Er3Al5O12 and Er4Al2O9. Both ErAlO3 and Er3Al5O12 displayed absorption in the visible light range. The calcination temperature had a greater effect on the red tone of ErAlO3 pigments than on Er3Al5O12. The main absorption peaks of Er3Al5O12 in the visible light range were blue-shifted, resulting in a slightly higher yellowness value b*. When zirconia was coloured with these two pigments, neither of them could stably exist at high temperatures. Er3+ might dissolve into the zirconia lattice to form a cubic fluorite solid solution (FSS), and the remaining Al2O3 phase was distributed in the zirconia solid solution matrix at high temperatures. If the pigment of ErAlO3 is added up to 5 wt%, the redness value a* reached the maximum value.