Minimizing Bond Angle Distortion to Improve Thermal Stability of Cr³⁺ Doped Near‐Infrared Phosphor

Abstract Broadband near‐infrared (NIR) phosphor‐converted light‐emitting diodes are next‐generation smart NIR light sources. However, the NIR phosphor suffers from serious thermal quenching (TQ), resulting in efficiency reduction and spectral shift. Here, a novel strategy is realized to suppress TQ by minimizing bond angle distortion, completely different from the conventional TQ suppression approach through bond length variation. Li(Sr 1− x Ca x )AlF 6 :Cr 3+ NIR phosphor is taken as an example in which rotation between the two parallel fluorine planes perpendicular to the C 3 axis in the [AlF 6 ] octahedron is found to dominate TQ. Increasing x from 0 to 1 reduces the amplitude of the rotation from 16.17° to 5.06°, weakening the electron–phonon coupling and, consequently, raising the TQ temperature significantly from 320 to 570 K. This mechanism is elucidated from both theoretical calculations and spectroscopic studies. The findings open a new horizon for the exploration of thermally stable NIR phosphors.