Unraveling the Remarkable Influence of Square Antiprism Geometry on Highly Efficient Far‐Red Emission of Eu3+ in Borotellurate Phosphors for Versatile Utilizations

Abstract Eu 3+ ‐activated red‐emitting inorganic phosphors have been favored highly for their classical 5 D 0 → 7 F J (J = 0, 1, 2, 3, 4) emissions. However, the fatal drawbacks of poor luminous efficacy and weak 5 D 0 → 7 F 4 transition persist, resulting in the ongoing challenge of achieving far‐red emission. This research reports series of highly efficient far‐red phosphors LnTeBO 5 (Ln = La 3+ , Y 3+ , Gd 3+ ):Eu 3+ with anomalously strong 5 D 0 → 7 F 4 transition, resulting from the distorted square antiprism [Ln/EuO 8 ]. Both the luminous efficacy and thermal stability can be greatly enhanced via the simple composition variation. [Ln/EuO 8 ] square antiprism‐triggered 5 D 0 → 7 F 2,4 transitions are elucidated in depth, acquiring ultra‐high luminous efficacy (IQE = 95%, EQE = 40%, and AE = 42%) and near‐zero thermal quenching (99%@150°C and 98%@200°C). Subsequently, the versatile utilizations in indoor lighting, plant growth lighting, and security ink are illustrated. This finding establishes a deep understanding for constructing high‐quality far‐red phosphors via the Eu 3+ ‐centered structural units of square antiprism.