Eu²⁺‐Doped Layered Double Borate Phosphor with Ultrawide Near‐Infrared Spectral Distribution in Response to Ultraviolet–Blue Light Excitation

Abstract Ultrabroadband near‐infrared (NIR) luminescent materials are important components for compact light sources used in food testing, medical and biosensing applications. A major long‐term challenge facing NIR luminescent materials is to design ultrabroadband phosphors activated by the rare‐earth ions characterized by the f–d transition. Here, an Eu²⁺‐doped Ba₃Lu(BO₃)₃ phosphor, showing peculiar luminescence characteristics such as a long emission wavelength ≈720 nm, a broader full width at half maximum of ≈197 nm, a large Stokes shift of ≈8300 cm^–1, and a longer decay time ≈5.58 µs, is reported. The smaller Eu²⁺ occupy the irregular and larger Ba²⁺ sites further reducing the symmetry, resulting in the increased splitting of the degenerate 5d level, thereby lowering the energy of Eu²⁺ emission. The longer decay time is also associated with the irregular Ba sites. This work improves the NIR mechanism of Eu²⁺ and opens up a new idea for exploring promising broadband NIR luminescent materials.