Abstract
Broadband near-infrared (NIR) light sources based on phosphor-converted light-emitting diodes are highly desirable for biochemical analysis and medical diagnosis applications. However, thermal quenching remains a demanding challenge for developing efficient NIR phosphors. Herein, we report the enhancement of both quantum efficiency and thermal stability in Cr(3+)-activated K(2)SrP(2)O(7) phosphors through a heterovalent substitution strategy by replacing Sr(2+) with Al(3+) in K(2)Sr(1-x) Al (x) P(2)O(7) (0.05 ≤ x ≤ 0.2) to obtain optimized broadband NIR emission. Structural modulation via Al(3+) substitution leads to the optimized composition, K(2)Sr(0.88)Al(0.1)P(2)O(7):0.02Cr(3+), which emits across a broad NIR range of 650-1100 nm peaking at 807 nm with a full width at half-maximum of ∼130 nm under 448 nm excitation. Remarkably, its emission intensity at 150 °C remains 120% of the initial value at room temperature, demonstrating a rare antithermal-quenching behavior. Temperature-dependent XRD studies further reveal that Al(3+) substitution effectively suppresses lattice expansion at elevated temperatures, indicating enhanced lattice stability under thermal excitation. Detailed structural and spectral analyses show that the substitution enhances local site symmetry, reduces electron-phonon coupling, increases thermally induced absorption probability, and fortifies energetic barriers against nonradiative transitions. These synergistic effects collectively endow this NIR phosphor with a superior thermal stability. Furthermore, NIR light-emitting diodes fabricated with this phosphor exhibit strong potential for applications in information identification, nondestructive detection, and night vision technologies. This study demonstrates a local structure engineering strategy for designing thermally robust Cr(3+)-activated NIR phosphors, offering valuable insights into material discovery and NIR spectroscopy device development.