Novel environmentally benign yellow inorganic pigments based on solid solutions of samarium-transition metal mixed oxides

Abstract

A new class of environmentally benign yellow inorganic pigments having the general formula Sm6-xW1-yZrxMoyO12+delta (x ranges from 0 to 0.6 and y ranges from 0 to 1) have been synthesized by a simple solid-state route and characterized by various spectroscopic techniques. The systematic substitution of Mo6+ for W6+ in Sm6WO12 gently shifted the absorption edge from 374 to 460 nm and consequently the designed compounds exhibited colors ranging from white to yellow. The band gap of the resultant pigments varied from 3.29 to 2.69 eV. The coloring mechanism is based on the O-2p-Mo-4d charge transfer transitions. Furthermore, the doping of Zr4+ for Sm3+ in Sm6MoO12 lattice produced intrinsic strain, which further red shifted the absorption edge to 479 nm. This intensified the yellow hue of the resultant compounds with band gap decreasing to 2.58 eV. The designed pigments possess good chromatic properties, especially the hue angle, which is found to be similar to those observed for industrial pigments such as PbCrO4, BiVO4, CdS, NiTiO3, and praseodymium yellow and also showed thermal and chemical stabilities. The coloring performance of the developed yellow pigments was evaluated by incorporating it into a polymer substrate material.