Achieving the Anomalous Far‐Red Emission of Eu3+ by Tailoring Distorted Square Antiprism Symmetry in Potassium‐Bismuth‐Phosphates

Abstract Eu 3+ doped phosphors with efficient and intense 5 D 0 ‐ 7 F 4 far‐red luminescence hold significant potential in daily and agricultural illuminations. However, Eu 3+ ions typically emit orange/red luminescence from 5 D 0 ‐ 7 F 1,2 transitions, and the development of high‐quality Eu 3+ doped far‐red phosphors is still lacking and challenging. Herein, two potassium‐bismuth‐phosphate phosphors are developed to manipulate the coordination geometry from octahedron to distorted square antiprism, achieving intense 5 D 0 ‐ 7 F 4 far‐red emission with a high quantum efficiency of 90.5%. Specifically, formation energy calculations and transient spectral measurements reveal that Eu 3+ occupies distorted square antiprism symmetric site in K 6 Bi 13 (PO 4 ) 15 :Eu 3+ , resulting in intense 5 D 0 ‐ 7 F 4 far‐red emission. Conversely, the octahedral symmetry generates weak 5 D 0 ‐ 7 F 4 emission in K 5 Bi(P 2 O 7 ) 2 :Eu 3+ . Moreover, K 6 Bi 13 (PO 4 ) 15 :0.08Eu 3+ (90%@423 K) exhibits better thermal stability compared to K 5 Bi(P 2 O 7 ) 2 :0.2Eu 3+ (83%@423 K). Spectral analyses and Debye temperature calculations exclude contributions from charge transfer band and structural rigidity, and elevated thermal stability is attributed to suppressed energy migration to quenching centers facilitated by smaller Eu 3+ doping level in K 6 Bi 13 (PO 4 ) 15 :0.08Eu 3+ . Finally, excellent photoelectric properties of white‐LEDs and plant growth lighting by utilizing the representative K 6 Bi 13 (PO 4 ) 15 :0.08Eu 3+ as red/far‐red components indicate its application potentiality. This work provides a feasible method for constructing efficient Eu 3+ doped far‐red phosphors.