Highly efficient near-infrared emission from Cr3+-sensitized double perovskite Cs2Ag0.6Na0.4InCl6:Tm3+ under visible light excitation

Abstract

The development of efficient near-infrared (NIR) luminescent materials excitable by visible light remains a significant challenge for practical applications in bioimaging and sensing. Here, we report a novel sensitization strategy to achieve high-efficiency NIR-II emission in lead-free halide double perovskites. Cr³⁺/Tm³⁺ co-doped Cs₂Ag_0.6Na_0.4InCl₆ single crystals were synthesized via a hydrothermal method. The introduced Cr³⁺ ions reside in a tailored weak crystal field of the Na⁺-alloyed host and exhibit strong absorption in the visible region. Furthermore, energy is effectively transferred from Cr³⁺ to Tm³⁺ activators, thereby overcoming the intrinsic limitation of weak f-f absorption in lanthanide ions. This strategy yields a remarkable enhancement of the characteristic Tm³⁺ emission at 1226 nm. The optimally doped phosphor, Cs₂Ag_0.6Na_0.4InCl₆: 30%Cr³⁺/30%Tm³⁺ (nominal feed ratios; actual doping concentrations: 0.14% for Cr³⁺ and 1.57% for Tm³⁺), achieves a high photoluminescence quantum yield (PLQY) of 35.8% under 340 nm excitation. The phosphor demonstrates excellent environmental stability, retaining 86.87% of its initial intensity after 210 days of storage under ambient conditions. A fabricated NIR phosphor-converted light-emitting diode (pc-LED) successfully enables proof-of-concept applications in non-destructive food freshness analysis and deep-tissue imaging. This work provides a fundamental design principle utilizing transition-metal sensitization in engineered perovskite hosts for high-performance, stable, and eco-friendly NIR light sources.