Pressure-Driven Eu²⁺-Doped BaLi₂Al₂Si₂N₆: A New Color Tunable Narrow-Band Emission Phosphor for Spectroscopy and Pressure Sensor Applications

A series of BaLi₂Al₂Si₂N₆ (BLASN): xEu²⁺ phosphors are successfully synthesized and their crystal structure and luminescence properties under varying hydrostatic pressures are reported herein. Structure variation is analyzed using in situ high-pressure X-ray diffraction and Rietveld refinements. Based on decay curves and Gaussian fitting of emission spectra, the presence of two photoluminescence centers is demonstrated. BaLi₂Al₂Si₂N₆: 0.01Eu²⁺ exhibits an evident peak position shift from 532 to 567 nm with an increase in pressure to ≈20 GPa. The possible factors and mechanisms for the variations are studied in detail. At a pressure of 16 GPa, BLASN: Eu²⁺ realizes a narrow yellow emission with a full width at half maximum of ≈70 nm. The addition of BLASN: Eu²⁺ (16 GPa) to the commercial white light-emitting diodes combination consisting of an InGaN chip, β-SiAlON: Eu²⁺, and red K₂SiF₆:Mn⁴⁺, can increase the color gamut by ≈15%, demonstrating the promising potential of pressure-driven BLASN: Eu²⁺ for wide-color gamut spectroscopy applications. Moreover, the emission shifts arising from pressure variation and the distinct color changes enable its potential utility as an optical pressure sensor; the material exhibits high pressure sensitivity (dλ/dP ≈ 1.58 nm GPa⁻¹) with the advantage of visualization.