The synthesis, characterization and optical properties of silicon and praseodymium doped Y6MoO12 compounds: Environmentally benign inorganic pigments with high NIR reflectance

Novel, yellow, brown and brick-red colored, near-infrared reflective pigments based on yttrium molybdate doped with metal ions such as Si4+ or Pr4+ are described. Replacing Si4+ for Y3+ in Y6MoO12 changed the color from light-yellow to dark-yellow and the band gap decreased from 2.60 to 2.45 eV due to O2p-Mo4d charge transfer transitions. In contrast, replacing Pr4+ for Y3+ changed the color from light-yellow to dark brown and the band gap shifted from 2.60 to 1.90 eV. The coloring mechanism is based on the introduction of an additional 4f1 electron energy level of Pr4+ between the valence and conduction bands. The NIR reflectance of the pigments on asbestos cement sheet was measured.