Cr3+ to Ln3+ energy transfer unlocks ultra-efficient NIR emission in Cs2NaLuCl6 single crystals

Developing efficient near-infrared (NIR) luminescence materials is crucial for next-generation NIR phosphor-converted light-emitting diodes (pc-LEDs). Cr 3+ -activated materials exhibit broadband NIR emission, however, they suffer from low efficiency and severe thermal quenching at wavelengths beyond 900 nm. To overcome these drawbacknd Membrane Technology, School of Chemical Engineering and Technology, Sun Yat-sen Uns, an efficient energy transfer pathway from Cr 3+ to Ln 3+ (Yb 3+ , Tm 3+ ) in Cs 2 NaLuCl 6 (CNLC) double perovskite single crystals was established. The Cr 3+ singly doped crystal shows broadband NIR emission peaking at 970 nm with an internal quantum efficiency (IQE) of 73.1%. Through effective Cr 3+ sensitization, the NIR-II emissions at 996 nm (Yb 3+ ) and 1222 nm (Tm 3+ ) are enhanced, along with the significantly improved luminescent thermal stability. Moreover, the co-doped system also exhibits superior IQE of 86.6% for CNLC:3 mol%Cr 3+ ,9 mol%Yb 3+ and 71.6% for CNLC:3 mol%Cr 3+ ,5 mol%Tm 3+ . The developed crystals integrated into a 540 nm-driven NIR LED delivers a NIR radiation power of 80.4 mW at a driving current of 600 mA, enabling high-resolution bioimaging and night vision applications. This work provides insight into energy transfer engineering to boost the luminescent efficiency and thermal stability in NIR-emitting materials.