Allochroic effect of praseodymium doped neodymium molybdate pigment synthesized by solid-state reaction

Abstract

This paper was to synthesize praseodymium-doped neodymium molybdate allochroic pigments with different molar ratios of molybdenum (Mo), neodymium (Nd) and praseodymium (Pr) through solid-state reactions. The pigments synthesized were investigated by X-ray diffraction (XRD), selected area electron diffraction (SAED), thermogravimetry and differential thermal analysis (TG-DSC), diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS) and colorimeter. The results show that a pure neodymium molybdate (i.e., Nd2MoO6) can be formed after sintering at 1000 °C for 3 h, and praseodymium-doped neodymium molybdate can be synthesized after sintering at 1000 °C for 3 h due to praseodymium ions entering in the lattice of Nd2MoO6. The crystal structure in the pigment synthesized can transform from cubic to tetragonal depending on the molar ratio of neodymium/molybdenum and sintering procedure. The color properties of pigments were measured in color space CIEL*a*b* under different standard illuminants (i.e., solar-light (D65), incandescent light (A), cool white fluorescent lamp (F2), and three-band fluorescent lamp (F11)). The results show that the colors of the pigments vary under different illuminants. According to the color difference (ΔE) analysis, neodymium molybdate pigment exhibits a maximum color difference of 10.69, and the maximum color difference of praseodymium-doped neodymium molybdate pigment with doping content of 0.2 increases to 17.63 due to the Pr3+ ions substitution for Nd3+ ions in the lattice. In addition, the color difference of the pigments with allochroic effect was discussed based on the colorimetry. The color difference of the pigments is due to a high reflectance region at 540–550 nm and a low reflectance region at 380–500 nm.