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• Co 2+ /Ni 2+ doped Li 2 ZnSiO 4 solid solutions were synthesized by solid state reaction. • Vivid blue coloration is achieved by d-d transitions of tetrahedral Co 2+ /Ni 2+ . • The as-prepared pigments exhibit excellent thermal stability. • Only 2 wt% pigment in PMMA provides a uniform and intense blue appearance. Solid solutions with the general formulas Li 2 Zn 1- x Co x SiO 4 (0 ≤ x ≤ 1) and Li 2 Zn 1- x Ni x SiO 4 (0 ≤ x ≤ 0.25) were successfully synthesized via a conventional high-temperature solid state reaction method. XRD confirmed the formation of phase-pure products, while XPS verified that both cobalt and nickel ions are present in the + 2 oxidation state. The undoped Li 2 ZnSiO 4 appeared white; however, even minor incorporation of Co 2+ or Ni 2+ ions induced a blue coloration in the resulting materials. UV–Vis–NIR spectroscopy revealed characteristic absorption bands associated with tetrahedrally coordinated Co 2+ or Ni 2+ ions, accounting for the observed blue color. TG-DTA analysis confirmed that the pigments exhibit thermal stability up to 1200 °C. Furthermore, the addition of only 2 wt% of the pigments into a transparent poly(methyl methacrylate) (PMMA) matrix produced vibrant blue composites, indicating their promising applicability in PMMA-based decorative materials.
Cheng et al. (Sat,) studied this question.