Crystal field engineering and energy transfer strategy for enhancing broadband near-infrared luminescence of Sm2+ activated oxynitride phosphors

Near-infrared (NIR) material is widely recognized for its significant application potential in bioimaging, anti-counterfeiting, and food quality inspection. Divalent rare earth ions are capable of producing broadband NIR emission in suitable host materials and offers high excitation absorption efficiency, owing to their parity allowed f-d transitions. Herein, Sm 2+ -activated SrAl 2 Si 3 O 4 N 4 oxynitride NIR phosphors are prepared, which exhibit a broad excitation band covering the entire visible region (300–650 nm) and a broadband NIR emission (700–1100 nm) peaking at approximately 800 nm. The substitution of Sr 2+ by Ba 2+ is implemented to regulate the local crystal field environment of Sm 2+ ions, thereby achieving a pronounced enhancement in NIR emission intensity. Furthermore, an energy transfer sensitization strategy from Yb 2+ to Sm 2+ is devised, by which an energy transfer efficiency of 70% was attained. The excitation absorption efficiency of BaAl 2 Si 3 O 4 N 4 :0.06Sm 2+ ,0.05Yb 2+ phosphor reached 54%, along with improved photoluminescence quantum efficiency and thermal stability. Finally, NIR pc-LED devices were fabricated using the optimal phosphor and blue LED chip, and demonstrate promising application in biological tissue imaging and detection. The proposed crystal field engineering and energy transfer strategy provides valuable insights for the design and development of NIR phosphors.