Synthesis of erbium-doped neodymium molybdate based inorganic pigments with high near-infrared reflectance and allochroic effect

A series of (Nd 1- x Er x ) 6 MoO 12 ( x  = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) pigments were synthesized via solid-state reactions. The pigments were characterized by X-ray diffraction (XRD), thermogravimetry and differential thermal analysis (TG-DSC), diffuse reflectance spectroscopy and colorimetry. The results show that erbium-doped rhombohedral neodymium molybdate (i.e., (Nd 0.8 Er0.2) 6 MoO 12 ) pigment with the maximum Δ E ∗ max of 18.48 and the NIR reflectance of 85.63 % synthesized under the optimum condition has an allochroic effect under different illuminants. Erbium ions doping in Nd 6 MoO 12 (R) is beneficial in improving the near-infrared (NIR) reflectivity and allochroic effect of the pigment. The temperature on the surface of aluminium panels coated with (Nd 1- x Er x ) 6 MoO 12 pigments is 17.2 °C lowder than that of aluminium panels uncoated due to the higher NIR reflectance of (Nd 1- x Er x ) 6 MoO 12 pigment for heat insulation. In addition, the chromaticity analysis of (Nd 0.8 Er0.2) 6 MoO 12 pigment reveals that the allochroic effect of the pigment is mainly affected due to the characteristic absorption peaks at wavelengths of 600 nm and 530 nm, and the influence of the characteristic absorption peaks at a wavelength of 600 nm on the allochroic effect of the pigment is more dominant rather than that of the characteristic absorption peaks at a wavelength of 530 nm.