Effect of molybdenum and praseodymium dopants on the optical properties of Sm2Ce2O7: Tuning of band gaps to realize various color hues

This paper reports on the synthesis, characterization and optical properties of a new class of rare earth based pigments as alternatives to toxic inorganic pigments. Investigations reveal that the doping of molybdenum for ceria in Sm2Ce2O7 changes the color hue from cream to yellow. The band gap of the resultant pigments decreases from 2.76 to 2.52 eV due to the O2p–Mo4d charge transfer transitions. On the other hand, the doping of praseodymium in ceria matrix changes the color from cream through brick red to dark brown and the band gap shifts from 2.76 to 1.72 eV. The coloring mechanism is based on the introduction of an additional electronic level of energy in the cerianite forbidden band. The influence of various mineralizers on the calcination temperature and optical properties of the pigments have been evaluated. The thermal and chemical stabilities of the pigments have also been examined.