High-Pressure Engineering for the Design of Ni²⁺-Based Phosphors.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Optical Materials

Background:

• High-pressure engineering can modify material properties beyond ambient conditions.
• Transition-metal phosphors are crucial for optical applications.
• Nickel(II) ions in oxides often exhibit interesting optical behavior.

Purpose of the Study:

• To investigate the effect of pressure and temperature on the optical properties of LiGaO2:Ni2+.
• To explore the structural transformation from beta-LiGaO2:Ni2+ to alpha-LiGaO2:Ni2+.
• To understand the mechanism behind pressure-induced shortwave infrared emission.

Main Methods:

• High-pressure and high-temperature synthesis and characterization.
• Temperature- and pressure-dependent photoluminescence, excitation, and lifetime measurements.
• Crystal-field analysis and Racah parameter calculations.

Main Results:

• Pressure- and temperature-induced transformation to alpha-LiGaO2:Ni2+ stabilizes Ni2+ in octahedral coordination.
• Intense broadband shortwave infrared emission observed from the alpha phase, originating from the 3T2 → 3A2 transition.
• The beta phase of LiGaO2:Ni2+ is optically inactive.
• Crystal-field analysis revealed a weak octahedral crystal field and moderate electron-lattice coupling in the alpha phase.
• Pressure-dependent evolution of Racah parameters indicated enhanced Ni2+ 3d electron localization and reduced covalency.

Conclusions:

• High-pressure engineering is an effective strategy for activating and tailoring optical properties of transition-metal phosphors.
• The study demonstrates a novel pathway for designing broadband Ni2+-based SWIR phosphors.
• Conventional Tanabe-Sugano diagrams may be insufficient for describing high-pressure effects on Ni2+ in oxides.