Broadband Near-Infrared Emission of Sm²⁺ in Highly Stable (Ba,Sr)Al₃Si₃O₄N₅ for Encryption and Nondestructive Inspection

Broadband near-infrared (NIR) phosphors show great promise in optoelectronics, night vision, and anticounterfeiting. Currently, mainstream transition-metal ions (Cr3+, Mn4+, etc.) and lanthanides (Nd3+, Yb3+, etc.) activated NIR phosphors suffer from the low absorption efficiency due to the spin-forbidden d-d or f-f transitions. Herein, we present a robust (Ba,Sr)Al3Si3O4N5:Sm2+ NIR phosphor that exhibits a broad-band peaking at 758 nm with high absorption efficiency stemming from the spin-allowed 4f-5d transition. The lowest excited level in 4f6 (5D0) is equivalent to the 4f55d1 of Sm2+, as evidenced by the temperature-dependent (5–300 K) emission spectra. The emission peaks of Sm2+ in these oxynitride phosphors can be tuned between 742 and 789 nm by simply changing the doping concentration. The optimized NIR phosphor exhibits excellent thermal and chemical stability, making it highly promising in encryption and nondestructive inspection. This work provides a pathway to exploring highly efficient and stable broadband Sm2+-doped NIR phosphors for optoelectronic applications.