Mo-Doped Cerium Gadolinium Oxide as Environmentally Sustainable Yellow Pigments

Abstract

Mo-doped Gd₁Ce_1–<i>x</i>O_3.5+<i>Y</i> (where <i>x</i> ranged from 0 to 0.3) oxides were synthesized as inorganic yellow pigments, which are benign and sustainable. The pigments exhibited good yellow color, with the yellowness value using the CIELAB 1976 system being around 39. In comparison to the existing reports on benign yellow pigments, which have been synthesized using high temperature calcination routes, this pigment has been synthesized through a low temperature sol–gel calcination route. The process also provided for a higher degree of size and shape control, leading to a bandgap of 2.82–2.52 eV. Size reduction to the nano level through the process provided a bottom up approach, where the presence of mineralizers enabled higher mass tone (<i>b</i>* value of around 80) at lower covering thickness. NIR solar reflectance, a measure of the ability of the pigment to contribute to energy savings by reflecting heat generating radiations of sunlight, was as high as 91%. The absence of toxic metal ions coupled with excellent chemical and thermal stabilities makes the developed pigment ideal for coloring plastics meant for children’s toys and ceramic surfaces that would come into immediate contact with human skin, such as bathroom tiles