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 (<i>I</i>_{423 K} = 21.18%). To address this thermal stability issue, a series of Lu_2+<i>z</i>Ca_1-<i>z</i>Al_4+<i>z</i>Ge_1-<i>z</i>O₁₂: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 <i>z</i> = 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.