Optical properties and application of blue and purple inorganic pigment powders based on cobalt/nickel doped Sr2MgSi2O7

In the present work, solid solutions of Sr 2 Mg 1- x Co x Si 2 O 7 (0.2 ≤ x ≤ 1) with blue coloration and Sr 2 Mg 1- x Ni x Si 2 O 7 (0.1 ≤ x ≤ 0.5) with purple coloration were successfully synthesized via solid state reactions. Rietveld refinement analysis confirmed the successful substitution of Mg 2+ by Co 2+ /Ni 2+ , as indicated by corresponding changes in cell volumes. These solid solutions display tunable blue and purple hues, influenced by the doping levels of Co 2+ /Ni 2+ . Compared to commercial cobalt blue (CoAl 2 O 4 ), the synthesized blue oxides significantly lowered Co 2+ levels while achieving the desired color properties. The rarity of purple coloration in nickel compounds makes this topic of particular interest. UV–Vis–NIR spectra revealed that the observed blue and purple colors arise from the A 2 4 ( F 4 ) → T 1 4 ( P 4 ) and T 1 3 ( F 3 ) → T 1 3 ( P 3 ) transitions of Co 2+ and Ni 2+ ions at tetrahedral sites, respectively. Furthermore, the thermal stability of the pigments was evaluated. To assess their compatibility with the polymer, 2 wt% of the as-prepared pigments were incorporated into poly(methyl methacrylate) (PMMA) to fabricate blue and purple PMMA composites, and their color properties were subsequently characterized. • Co/Ni doped Sr 2 MgSi 2 O 7 solid solutions were synthesized by solid state method. • The resulting powders exhibit vivid blue and purple hues. • These pigments demonstrate good thermal stability. • Their colors arise from d-d electron transitions in Co 2+ /Ni 2+ tetrahedral sites. • The pigments show excellent coloring properties in PMMA composites.