Novel and environment-friendly high NIR reflectance color pigments based on Fe, Pr, Ho, Nd, Er and Ce doped lithium aluminum molybdate: Synthesis and properties

This paper reports the syntheses of a series of polychromatic pigments with the general formula LiAl1-xMx(MoO4)2 (M = Fe, Pr, Ho, Nd, Er, Ce; x = 0–0.4) and the characterization of near-infrared reflectance properties. The synthesized pigments exhibited green (Pr), lavender (Nd), pink (Er) and different yellows (Fe, Ho, Ce). The XRD patterns of typical LiAl1-xFex(MoO4+δ)2 samples show that the prepared samples are triclinic lithium aluminum molybdate structures with space group P-1.The iron in the sample mainly existed in the form of Fe3+, which led to the directional growth of grains with different morphologies. The near-infrared solar reflectance (R*%) of LiAl1-xFex(MoO4)2 pigments reached 94.19%. As the doping concentration of rare earth was increased, the color of the pigments gradually deepens. By introducing rare earth elements Pr, Ho, Nd, Er, and Ce into the LiAl(MoO4)2 matrix, the color of the pigment was successfully changed from white to green, lavender, pink, and yellow, indicating that doping can control the color of the pigment. Moreover, the prepared pigments had high R*% (>87%), indicating that the pigment samples have excellent thermal insulation properties and can be used as a new type of reflective thermal insulation coatings.