Enhanced near-infrared emission in Na2ZnSiO4:Fe3+ via lattice engineering toward highly sensitive fluorescence lifetime thermometry

Fe3+-activated near-infrared luminescent materials are gaining interest for applications in night vision, bioimaging, and food analysis. Although Fe3+ is often considered a luminescence quencher, proper control can make it an efficient activator. In this study, a novel Na2Zn0.7Mg0.3SiO4:0.003Fe3+ (NZMS:0.003Fe3+) phosphor was synthesized by substituting Mg2+ for Zn2+ in the Na2ZnSiO4 host. Upon 280 nm excitation, NZMS:0.003Fe3+ exhibits a broad emission band centered at 720 nm. The substitution of Zn2+ with Mg2+ induces lattice distortion and lowers the local symmetry of Fe3+ centers, resulting in a 6.4-fold enhancement in photoluminescence intensity at the optimal concentration (x = 0.3). The optimized NZMS:0.003Fe3+ phosphor shows high thermal sensitivity in the 300–362 K range, with a maximum relative sensitivity of 3.40% K−1 at 357 K. Based on this, a fiber-optic system for fluorescence lifetime thermometry was designed. Its high sensitivity and robust lifetime-based detection show great potential for minimally invasive biomedical procedures and printed circuit board monitoring. This work provides a strategy for enhancing Fe3+ luminescence and explores new applications for Fe3+-doped phosphors.