Enhancement of Blue‐Light‐Excited NIR‐II Emission of Er ³⁺ in Double Perovskites via Mo ⁴⁺ Sensitization

Abstract Phosphors with efficient blue‐light absorption and near‐infrared (NIR) emission conversion capabilities are essential for high‐performance phosphor‐converted NIR LEDs. Herein, a novel strategy for enhancing blue‐light absorption and Er 3+ NIR‐II emission in double perovskites via Mo 4+ sensitization is developed. Density functional theory calculations reveal that the introduction of Mo 4+ contributes Mo 4d orbitals to the conduction band minimum (CBM), narrowing the bandgap and enabling strong blue‐light absorption. The large absorption cross‐section of Mo 4+ effectively overcomes the limitation of narrow 4f‐4f absorption transitions in Er 3+ . Under blue light excitation, Mo 4+ /Er 3+ co‐doped Cs 2 NaBiCl 6 double perovskite phosphors exhibit broadband emission from Mo 4+ at ∼900 nm along with intrinsic emissions from Er 3+ at ∼1000 nm and ∼1540 nm. Efficient energy transfer from Mo 4+ to Er 3+ boosts the NIR emission at ∼1540 nm by 36.09 times compared to Er 3+ single‐doped sample. The optimized phosphor (Cs 2 NaBiCl 6 :20%Mo 4+ /30%Er 3+ ) achieves a total NIR‐II PLQY of 68.7%, with 34.8% at ∼1540 nm. Integrated with a commercial blue LED chip, an efficient NIR‐II LED achieving a maximum photoelectric conversion efficiency of 13.26% is demonstrated, highlighting potential in anti‐counterfeiting, non‐destructive inspection, and night vision. These results open a novel pathway for efficient sensitization in blue‐light‐excitable NIR phosphors.