Multifunctional Cr³⁺ Ion-Activated Sr₂Sc₂B₄O₁₁ Broadband Near-Infrared Phosphor with High Luminescence Thermal Stability through the Deformation Constraint

Broadband near-infrared (NIR) phosphors emitting in the 700–1000 nm range find extensive applications in night vision, medical image, and food analysis. High luminescence thermal stability of their spectra is crucial for maintaining consistent and reliable output under various thermal conditions. Microcrystalline powders of Sr2Sc2B4O11:Cr3+ are synthesized, and their photoluminescence (PL) properties are studied as functions of Cr3+ concentration, temperature, and excitation power. The energy band structure and phonon density of states of the Sr2Sc2B4O11 lattice are studied theoretically. It is revealed that Sr2Sc2B4O11 is an indirect bandgap material with a bandgap of 3.16 eV. Sr2Sc2B4O11:Cr3+ shows broadband NIR emission centered at 825 nm upon 455 nm excitation with lifetimes on the order of 100 μs from 80 to 600 K. The PL shows good luminescence thermal stability with a quenching temperature of 380 K. Notably, 57% of the room-temperature PL intensity is retained at 423 K. The high luminescence thermal stability of the PL may be attributed to the constraint on the deformation of ScO6 polyhedra through the formation of dimers. A luminescence thermometer based on the lifetime of Sr2Sc2B4O11:Cr3+ is proposed. It is determined that the relative sensitivity of the thermometer increases gradually from 80 to 600 K and exceeds 0.5% K–1 starting from 300 K.