Red ceramic pigments of terbium-doped ceria prepared through classical and non-conventional coprecipitation routes

Reddish ceramic pigments based on cerianite compositions Ce1−xTbxO2 (x = 0.1, 0.2 and 0.3) and Ce0.9Tb0.05Y0.05O2 have been prepared. Firstly, the optimal composition giving the best red colour was selected (Ce0.9Tb0.1O2) from ceramic and chlorides coprecipitation samples fired at 1100–1500 °C. Secondly, the effect of using different classical and non-conventional coprecipitation routes on the synthesis and colouring performance of CeO2-Tb red pigments was analyzed for the first time. In addition to classical coprecipitation we tested also the use of hydrothermal treatment and other more homogeneous coprecipitation methods with oxalates and urea. Homogeneous coprecipitation was also combined with ultrasonic or microwave irradiation. Samples were characterized by thermal analysis, XRD, SEM/EDX, optical spectroscopy and colour measurements. Interestingly, the optimization of synthesis methods enabled to obtain more homogeneous (single phase) CeO2-Tb solid solutions at lower temperatures (400–1100 °C), exhibiting very nice reddish colourations associated to lower energy bandgaps (Eg below 2.30 eV). The obtained optimal compositions could be therefore alternative candidates as environmentally friendly reddish ceramic pigments.