Optical characteristics and application of cobalt/nickel doped SrZn2(PO4)2 blue-violet and violet inorganic pigment powders

Abstract

Blue-violet and violet inorganic pigments, derived from SrZn2-xCox(PO4)2 (0 ≤ x ≤ 1) and SrZn2-xNix(PO4)2 (0 ≤ x ≤ 0.5) solid solutions, were successfully synthesized via a solid-state reaction. The structure, color, optical properties, and potential applications of the synthesized pigments were systematically characterized. All pigments crystallized in a single-phase structure. Rietveld refinement analysis confirmed the successful substitution of Zn2+ by Co2+/Ni2+ in the lattice. Based on the XPS and UV–Vis–NIR analyses revealed that the coloration of Co2+/Ni2+ doped SrZn2(PO4)2 originates from d-d electronic transitions in a tetrahedral coordination environment. Compared to commercial purple pigments, such as Co3(PO4)2 and NH4MnP2O7, the synthesized pigments exhibit superior thermal stability and require lower cobalt or nickel doping levels. Furthermore, 2 wt% of these pigments were incorporated into poly(methyl methacrylate) (PMMA) plastic to form blue-violet and violet composites, whose color and optical properties were systematically analyzed.