Achieving spectrally tunable and thermally stable near-infrared emission in Fe3+-activated spinel phosphors via the cation site modulation strategy.

Environment-friendly Fe³⁺ ions as near-infrared (NIR) activators have recently attracted considerable interest in intelligent NIR light source field; however, designing wavelength-tunable and thermally stable Fe³⁺-doped NIR luminescence material remains a daunting challenge. Here, by selecting a spinel compound as the host, a series of Mg_1−yAl_2+yO₄:Fe³⁺ NIR phosphors featuring tunable wavelengths and high thermal stability is developed using a cation site modulation strategy. Through Mg²⁺/Al³⁺ chemical substitution to modify the local crystal environment and the site occupation of Fe³⁺, the emission peak can be adjusted from 730 to 770 nm along with a greatly enhanced emission intensity. The emission redshift and intensity increase mechanism of the as-prepared phosphors is revealed by structural analyses. The emission intensity of Mg_0.87Al_2.13O₄:Fe³⁺ at 423 K can maintain 85.13% of the initial intensity at room temperature. The synergistic effect of weak electron–phonon coupling effect, high structural rigidity, and large bandgap renders excellent anti-quenching properties to the developed phosphors. Additionally, the as-prepared phosphors demonstrated great potential in the non-destructive detection and quantitative analysis of Cu²⁺ contents. This work provides a new design principle toward the optical property optimization of Fe³⁺-activated NIR materials for multiple photonic applications. [ABSTRACT FROM AUTHOR]