Synthesis and optical properties of new highly NIR reflective inorganic pigments RE6Mo2O15 (REÂ =Â Tb, Dy, Ho, Er)

Novel near-infrared (NIR) reflecting pigments with colors ranging from yellow to orange to dark brown based on the rare earth molybdenum oxides RE6Mo2O15 (RE = Tb, Dy, Ho, Er) are described. The compounds were prepared by solid state reactions and characterized by XRD analysis and UV-Vis-NIR diffuse reflectance spectroscopy. The compounds RE6Mo2O15 (RE = Tb-Er) crystallize in a trigonal crystal structure with the cell parameters a = 737.6(2)-745.7(2) pm and c = 932.3(1)-946.4(1) pm. For the pigments Er6Mo2O15 and Ho6Mo2O15, optical and detailed color analysis revealed illuminant-dependent, color changing behavior (orange/yellow). Different light emitting sources such as classical bulb, LED, fluorescence lamp, and solar light were used for the characterization of these pigments. A brilliant yellow color hue was obtained for Dy6Mo2O15, whereas Tb6Mo2O15 exhibited a dark brown color. High NIR solar reflectance of 51.1%-98.1% were obtained for Tb6Mo2O15 and Ho6Mo2O15, respectively (recorded in the range between 700 and 2500 nm by using PTFE as reference).