High-Pressure Engineering for the Design of Ni ²⁺ -Based Phosphors

High-pressure engineering provides a powerful strategy to activate and tailor the optical properties of transition-metal-based phosphors beyond the constraints of ambient-pressure crystal chemistry. Here, we demonstrate that pressure- and temperature-induced structural transformation of β-LiGaO 2:Ni 2+ to α-LiGaO 2:Ni 2+ stabilizes Ni 2+ ions in an octahedral coordination environment, enabling intense broadband shortwave infrared (SWIR) emission arising from the spin-allowed 3 T 2 → 3 A 2 transition of the d 8 electronic configuration. In contrast, the as-prepared low-pressure β-LiGaO 2:Ni 2+ phase remains optically inactive. Temperature- and pressure-dependent photoluminescence, excitation, and lifetime measurements, combined with crystal-field analysis, reveal a weak octahedral crystal field, moderate electron–lattice coupling, and a pressure-dependent evolution of the Racah parameters in α-LiGaO 2:Ni 2+ . Accounting for this evolution exposes a fundamental limitation of conventional Tanabe–Sugano diagrams, showing that the commonly anticipated 1 E– 3 T 2 crossover is shifted to much higher pressures or may become experimentally inaccessible. The unexpected increase of the Racah parameter B with pressure indicates enhanced localization of Ni 2+ 3 d electrons and reduced metal–ligand covalency. These results establish high-pressure engineering as an effective pathway for designing broadband Ni 2+ -based SWIR phosphors.