Synthesis and characterization of a new high NIR reflective ytterbium molybdenum oxide and related doped pigments

A novel yellow NIR reflecting pigment with the formula Yb6Mo2O15 crystallizing in a trigonal structure with the color coordinates L* = 88.7, a* = −6.6, b* = 55.0, C* = 55.4, and h° = 96.8 is described. Color variation from pale yellow to brick-red was realized by partial substitution of Yb3+ or Mo6+ with various metal ions. The novel pigments of the formula Yb6−xDxMo2O15±δ (D = Na, Ca, Ti, Bi) and Yb6Mo2−xMxO15−δ (M = Na, Fe, Co, Nb, Bi) were characterized by powder XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The high NIR solar reflectance of Yb6Mo2O15 of 93.7% (PTFE used as reference) was further improved with Yb5.4Ti0.6Mo2O15+δ and Yb6NbMoO15−δ reaching values of 99.4%, and 99.7%, respectively. Finally, the potential of the new rare earth molybdenum oxides for use as cool pigments in rooftop applications was demonstrated by the developed brick-red compound Yb6Mo1.6Fe0.4O15−δ having an enlarged band gap of 2.46 eV in comparison to 2.3 eV for Yb6Mo2O15. Furthermore, Yb6Mo1.6Fe0.4O15−δ exhibits an impressive NIR reflectivity of 90.4%.