Wavelength-Tunable of Broad Red to Near-Infrared Emission in (Sr,Ba)3Sc4O9 :Eu2+ Phosphors: Crystal Field Effects and Thermal Stability

In this work, a series of Eu²⁺-activated phosphors, including Sr₃Sc_4-xO₉:xEu²⁺, Ba_3(1-y)Sr_3ySc_3.985O₉:0.015Eu²⁺ (0 ≤ y ≤ 1), and Ba₃Sc_4-xO₉:xEu²⁺, were successfully synthesized via a sol-gel method. The Sr₃Sc_4-xO₉:xEu²⁺ phosphors exhibited a broad red emission band centered at 609 nm under 430 nm blue-light excitation, with a measured internal quantum yield of 47.94%. Upon partial substitution of Sr²⁺ by Ba²⁺ in Sr₃Sc_3.985O₉:0.015Eu²⁺, a pronounced redshift in the emission maximum was observed, extending from 609 to 843 nm and thereby covering the entire visible to near-infrared (NIR) spectral range, corresponding to a total shift of 234 nm. Structural analysis indicates that the emission behavior of Eu²⁺ is strongly influenced by its coordination environment within [Sr/Ba1O₆] and [ScO₆] octahedra, which exhibit low-symmetry fields and induce substantial crystal field splitting (CFS). Thermal quenching behavior was evaluated by monitoring emission intensity at 150 °C, where Sr₃Sc_3.985O₉:0.015Eu²⁺, Sr_1.5Ba_1.5Sc_3.985O₉:0.015Eu²⁺, and Ba₃Sc_3.985O₉:0.015Eu²⁺ retained 85.8%, 75.1%, and 65.8% of their room-temperature luminescence, respectively. These findings demonstrate excellent thermal stability and tunable red-to-NIR emission, establishing this phosphor family as a promising candidate for next-generation NIR-emitting materials and photonic applications.