Synthesis and optical properties of Ce0.95Pr0.05−xMxO2 (M = Mn, Si) as potential ecological red pigments for coloration of plastics

Ecological red pigments Ce0.95Pr0.05−xMxO2 (M = Mn, Si) have been synthesized by conventional solid-state route and characterized by X-ray diffractometer, scanning electron microscope and UV–vis spectroscopy. Mn4+/Si4+ was incorporated into the CeO2–PrO2 system to tune the color properties of the pigments by shifting the optical absorption edge. Si4+ substitution blue shifts the absorption edge of Pr-doped ceria and shows bright reddish brown color. Mn4+ substitution stabilizes the absorption edge and exhibits dark brown hue. The coloring mechanism is based on the shift of charge transfer band of CeO2 to higher wavelength by co-substitution of Pr4+ and tetravalent metal ions in ceria. Si co-doped pigments possess smaller particles and hence exhibit more lightness compared to Mn co-doped samples. The reddish brown pigments exhibit very good coloring performance in polymer matrix. These Ce0.95Pr0.05−xMxO2 (M = Mn, Si) pigments have potential to be used as ecological red pigments for coloration of plastics.