Multiband excited bright NIR emitter via Yb3+/Cr3+ co-doped double perovskites for multimodal anti-counterfeiting and imaging

Near-infrared (NIR) luminescence, particularly in the 700–1100 nm range, holds great promise for applications in night vision, biomedical imaging, and anti-counterfeiting due to its deep tissue penetration, low scattering, and non-invasive nature. Yb³⁺ ions feature a sharp NIR emission at ∼1000 nm, but their parity-forbidden 4f-4f transitions lead to weak absorption and poor excitation efficiency under ultraviolet–visible light. To overcome these limitations, we report a Cr³⁺ co-doping strategy to enhance the NIR emission efficiency and excitation bandwidth of Yb³⁺ in lead-free double perovskite Cs₂NaScCl₆ microcrystals synthesized via a hydrothermal method. The introduction of Cr³⁺ ions generates additional electronic states, reduces the band gap, and significantly broadens the excitation range from the ultraviolet to the visible region. Combined spectroscopy and theoretical calculations demonstrate the energy transfer from Cr³⁺ to Yb³⁺ with a high transfer efficiency of 45.51 %, leading to an 8.15-fold enhancement in NIR emission intensity compared to samples doped solely with Yb³⁺. The co-doped system exhibits efficient multi-band excitation and strong NIR emission, enabling its application in NIR phosphor-converted light-emitting diodes and anti-counterfeiting. This work provides a promising strategy for developing efficient, broadband-excitable NIR phosphors and advancing lead-free optoelectronic devices.