Environment-friendly red pigments from CeO2–Fe2O3–Pr6O11 solid solutions

Abstract

New inorganic pigments based on CeO2–Fe2O3–Pr6O11 solid solutions were synthesized and their color properties were assessed from the view point of possible environmentally benign nontoxic red pigments. A wide range of compositions, Ce0.9FexPr0.1−xO2−δ (x ranges from 0.02 to 0.095) and Ce0.8FexPr0.2−xO2−δ (x ranges from 0.04 to 0.19) were prepared and characterized by powder X-ray diffraction, lattice parameter measurements, electron microscopy (SEM/EDAX), UV–vis spectroscopy and L*, a*, b* color measurements. The prepared solid solutions absorb the visible blue and green under 600 nm efficiently, which is originated from the shift of charge transfer band in CeO2 by co-substitution of iron and praseodymium for cerium. The optical absorption edge of these pigments depends on the Pr and Fe content and was found to shift their absorption edge towards the lower energy or higher energy side as the co-substitution of praseodymium increases or iron increases for cerium with the band gap changing from 1.81 to 1.97 eV as a result the pigments show brick red to dark brown. Effective red hue was obtained for Ce0.9Fe0.04Pr0.06O1.95 and Ce0.8Fe0.08Pr0.12O1.9 compositions, which exhibit better L*, a*, and b* values (55, 18.30, and 21.55) and (43, 18.67, and 17.40), respectively. In addition, they present a much lower toxicity than cadmium sulfoselenide based red pigments, because they are composed of non-toxic and safe elements.