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 Sr3Sc4-xO9:xEu2+, Ba3(1–y)Sr3ySc3.985O9:0.015Eu2+ (0 ≤ y ≤ 1), and Ba3Sc4-xO9:xEu2+, were successfully synthesized via a sol–gel method. The Sr3Sc4-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 Sr3Sc3.985O9:0.015Eu2+, 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 Sr3Sc3.985O9:0.015Eu2+, Sr1.5Ba1.5Sc3.985O9:0.015Eu2+, and Ba3Sc3.985O9:0.015Eu2+ 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.