Mo-doped Gd 1 Ce 1−x O 3.5+Y (where x 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 (b* 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.

Increasing energy cost calls for exterior coatings with high near infra-red reflectance, so as to reduce heat absorption and in turn cost of air-conditioning. While modulations of substrate, use of white metal oxides as pigments or under-layers has been reported in past, reports on metal oxide or doped metal oxide pigments with high NIR reflectance is scarce. We report for the first time a blue colored cobalt aluminate type pigment prepared through doping of cerium, praseodymium or neodymium. CIELAB color measurements and calculation of E indicated that the Nd doped sample had crystal size of (36±1) nm, bandgap value of (2.4±0.2) eV and color coordinates similar to that of cobalt aluminate. The molar ratio as estimated by EDX was found to be Al : Cu : Co : Ce : Nd : O= 2 : 0.06 : 0.06 : 0.012 : 0.000 12 : 6.18. The pigment was found to have potential applications as a cool blue colorant, owing to changes in optical properties arising out of crystal chemistry changes. Incorporation of rare earth metal ions was found to enhance the NIR reflectance by 10%, when compared to a conventional cobalt aluminate pigment. The oxide has been well characterized and its performance as a pigment evaluated. We have proposed that changes in crystal lattice when neodymium enters into Ce 4+ sites enhance the NIR reflectance by about 9% as against the entry of praseodymium.