High-Pressure Near-Infrared Luminescence Studies of Fe³⁺-Activated LiGaO₂

A 0.25% iron (Fe³⁺)-doped LiGaO₂ phosphor was synthesized by a high-temperature solid-state reaction method. The phosphor was characterized utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure photoluminescence, and photoluminescence decay measurement techniques using diamond anvil cells (DACs). The powder X-ray analysis shows that the phosphor is a β polymorph of LiGaO₂ with an orthorhombic crystallographic structure at room temperature. The SEM result also confirms the presence of well-dispersed micro-rod-like structures throughout the sample. The photoluminescence studies in the near-infrared (NIR) range were performed at ambient, low-temperature, and high-pressure conditions. The synthesized phosphor exhibits a photoluminescence band around 746 nm related to the ⁴T₁ → ⁶A₁ transition with a 28% quantum efficiency at ambient conditions, which shifts toward longer wavelengths with the increase of pressure. The excitation spectra of Fe³⁺ are very well fitted with the Tanabe-Sugano crystal-field theory. The phosphor luminescence decays with a millisecond lifetime. The high-pressure application transforms the β polymorph of LiGaO₂ into a trigonal α structure at the pressure of about 3 GPa. Further increase of pressure quenches the Fe³⁺ luminescence due to the amorphization process of the material. The prepared phosphor exhibits also mechanoluminescence properties in the NIR spectral region.