Stable Polyhedron-Cluster-Based Rigid Fluoride Framework toward Zero-Thermal-Quenching Near-Infrared Emission for Prolonged LED Applications
Konglan Chen, Shiyu Jia, Xueliang Zhang, Zifan Shao, Yayun Zhou, Ting Fan, Ting Yu, Tingting Deng
Abstract
Development of highly thermally stable broadband near-infrared (NIR) luminescence materials is crucial for advancing the prolonged stable application of smart NIR light sources. In this study, a zero-thermal-quenching and reversible temperature-dependent broadband NIR-emitting Cs 2 NaAl 3 F 12:Cr 3+ phosphor is demonstrated, benefiting from its stable polyhedron-cluster-building rigid structure. The excellent thermal stability of Cs 2 NaAl 3 F 12:Cr 3+ is rooted in its stable [Al 6 Na 4 F 45 ] cluster building unit, which provides a rigid structure with a weak electron–phonon coupling effect and a wide band gap with a huge thermal activated barrier. Such characteristics are well revealed by multiple studies on crystal structure, electronic structure, Huang–Rhys factor S, configuration coordinate model, and Debye temperature. The incorporation of Li or K instead of Na weakens the luminescence thermal stability, directly proving the importance of the stable [Al 6 Na 4 F 45 ] cluster for stable Cr 3+ substitution and rigid structure construction. Furthermore, Cs 2 NaAl 3 F 12:Cr 3+ presents much superior thermal stability compared to traditional rigid garnet-type fluorides Na 3 X 2 Li 3 F 12:Cr 3+ (X = Al, Ga, In). A high-power NIR LED is presented, utilizing the high quantum efficiency (∼71%) and extremely thermally stable broadband NIR emission around 750 nm of Cs 2 NaAl 3 F 12:Cr 3+ . It realizes clear vein and cartilage imaging in the human hand, demonstrating its potential in medical diagnosis applications. This result provides important insights for designing new-type rigid crystal structures using stable polyhedron clusters as basic units, advancing the development of highly thermally stable NIR-emitting phosphors.