Blue pigment based on Ni-doped Zn2GeO4: Addressing structure and electronic properties by combining experiment and theory

Understanding the process of color development and creating practical and efficient blue pigments is crucial in ceramics. The current work describes the synthesis and characterization of Ni2+-doped Zn2GeO4 samples with varying concentrations (x = 0, 0.01, 0.02, 0.04, 0.08 and 0.16 mol%) as an effective strategy for tailoring their structure and electronic properties. These materials were synthesized using the coprecipitation method followed by microwave-assisted hydrothermal treatment at 140 °C for 10 minutes, and the as-synthesized samples underwent heat treatment at 1000 °C for 2 hours to establish thermal-colorimetric stability. The synergistic effect of the Ni2+ 3d orbitals generating energy levels as new trapping sites in a broad energy range above the valence band was verified using DFT calculations. The substitution of Zn2+ by Ni2+ at x = 0.01% changes the local electronic structure, resulting in a switchable electron transfer from the [NiO4] and the neighbor [ZnO4]and [GeO4] tetrahedral clusters to shared oxygen anions, which is responsible for the observed blue color, as confirmed by colorimetric and spectroscopic analysis. This study paves the way, shedding light on the strategic design of a new class of ceramic pigments characterized by low toxicity, a vibrant blue hue, and excellent chemical/thermal durability. Furthermore, it provides a robust platform for exploring its potential application in the color-tunable Zn2GeO4-based materials.