Engineering broadband near-infrared emission via the strategic assembly of Cr³⁺ ion pairs in aluminum-based spinels

Broadband near-infrared (NIR) phosphors have emerged as essential components for next-generation portable and intelligent NIR lights. Nevertheless, the concurrent realization of long-wavelength emission (LWE), wide bandwidth, and high performance remains challenging. Herein, a combined strategy of engineering crystal field and assembling Cr³⁺ ion pairs within Zn_1-xMg_xAl₂O₄ spinel solid solutions synergistically induces the evolution of Cr³⁺ emission from sharp red (<i>λ</i>_em = 709 nm, bandwidth = 24 nm) to broadband NIR region (<i>λ</i>_em = 890 nm, bandwidth = 283 nm). The coupling of the excited energy state and the interception of excited electrons account for the target broadband NIR LWE, achieving high thermal stability (I_{423 K}/I_{298 K} = 70.8%). Encapsulating the optimized NIR phosphors into prototype phosphor-converted light-emitting diodes (pc-LEDs) achieves 65.26 mW NIR radiant flux at 1400 mA, with a photoelectric conversion efficiency (PCE) of 8.12% at 30 mA, facilitating online fruit moisture detection, non-invasive bioimaging, and night vision applications.