Sensitizing effect of lanthanide luminescence by Mo4+/Ag+ in double perovskites: great enhancement of near-infrared emission via wide range of excitation (250–850 nm)

Lead-free halide double perovskites (LFHDPs) have gained prominence as eco-friendly optoelectronic materials due to their structural stability and flexible tunability. Lanthanide (Ln³⁺) ions have rich energy levels, which can endow LFHDP materials with emissions ranging from visible to near-infrared (NIR) region through the ion doping strategy. However, their NIR applications remain limited by narrowband emission and low photoluminescence quantum yield (PLQY) due to weak absorption cross-section. Herein, Cs₂NaInCl₆:Ln³⁺ were successfully synthesized, and the problem of low absorption of Ln³⁺ ions is effectively solved. Incorporating Mo⁴⁺/Ag⁺ ions achieves a near-unity PLQY and expands the excitation spectrum across the full visible range and a small part of NIR region (250-850 nm). Mechanism analysis revealed synergistic energy transfer pathways involving self-trapping excitons and intermediate energy states of Mo⁴⁺ ion, enhancing both photon absorption and PLQY. The universal applicability of this approach has been validated across Bi-based and multiple lanthanide ions (Ln: Ho, Er, Tm, Yb). These optimized materials demonstrate exceptional broadband emission characteristics suitable for multi-scenario NIR applications, including light-emitting-diodes (LEDs), night vision, imaging, anti-counterfeiting technologies. This co-doping methodology establishes a versatile framework for overcoming inherent limitations in Ln³⁺-activated materials, offering new possibilities for efficient NIR optoelectronic devices.