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

Abstract

AbstractEu3+ doped phosphors with efficient and intense 5D0‐7F4 far‐red luminescence hold significant potential in daily and agricultural illuminations. However, Eu3+ ions typically emit orange/red luminescence from 5D0‐7F1,2 transitions, and the development of high‐quality Eu3+ 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 5D0‐7F4 far‐red emission with a high quantum efficiency of 90.5%. Specifically, formation energy calculations and transient spectral measurements reveal that Eu3+ occupies distorted square antiprism symmetric site in K6Bi13(PO4)15:Eu3+, resulting in intense 5D0‐7F4 far‐red emission. Conversely, the octahedral symmetry generates weak 5D0‐7F4 emission in K5Bi(P2O7)2:Eu3+. Moreover, K6Bi13(PO4)15:0.08Eu3+ (90%@423 K) exhibits better thermal stability compared to K5Bi(P2O7)2:0.2Eu3+ (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 Eu3+ doping level in K6Bi13(PO4)15:0.08Eu3+. Finally, excellent photoelectric properties of white‐LEDs and plant growth lighting by utilizing the representative K6Bi13(PO4)15:0.08Eu3+ as red/far‐red components indicate its application potentiality. This work provides a feasible method for constructing efficient Eu3+ doped far‐red phosphors.