Near-Infrared Phosphors with Significantly Improved Luminescence Intensity and Zero-Thermal-Quenching for Light-Emitting Diodes

The development of near-infrared (NIR) phosphors with augmented luminous efficiency and robust thermal stability holds pivotal importance for high-performance NIR lighting sources. Herein, Ln2CaGa4GeO12:Cr3+ (Ln = Lu, Y, and Gd) compounds are successfully synthesized, and the one with Ln = Lu shows the most intense emission. Subsequently, the luminescence properties of Lu2CaGa4GeO12:Cr3+, which are contingent upon the Cr3+ concentration, are meticulously examined. It is found that replacing Ga3+ with Al3+ can remarkably boost the emission intensity of Lu2CaGa4GeO12:Cr3+. Specifically, the emission intensity of Lu2CaAl4GeO12:Cr3+ is 3.69-fold that of Lu2CaGa4GeO12:Cr3+. Nevertheless, despite the high emission intensity of Lu2CaAl4GeO12:Cr3+, its thermal stability is rather poor (I423 K = 21.18%). To address this thermal stability issue, a series of Lu2+zCa1-zAl4+zGe1-zO12:Cr3+ solid solutions are ingeniously designed through the cosubstitution of Ca2+-Ge4+ by Lu3+-Al3+. This innovative design effectively optimizes the electron population and endows the material with thermal quenching characteristics. Significantly, the sample with z = 0.3 maintains nearly 100% of its emission intensity at 423 K when compared with that at room temperature, manifesting a rare zero-thermal quenching performance. Finally, NIR LEDs fabricated by using these optimized phosphors display substantial potential for applications in fields such as nondestructive detection and night vision.