Ultra‐efficient broadband near‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) are urgently needed to improve the detection sensitivity and spatial resolution of current smart NIR spectroscopy‐based techniques. Nonetheless, the performance of NIR pc‐LED has severely limited owing to the external quantum efficiency (EQE) bottleneck of NIR light‐emitting materials. Herein, a blue LED excitable Cr3+‐doped tetramagnesium ditantalate (Mg4Ta2O9, MT) phosphor is advantageously modified through lithium ion as a key efficient broadband NIR emitter to achieve high optical output power of the NIR light source. The emission spectrum encompasses the 700–1300 nm electromagnetic spectrum of first biological window (λmax = 842 nm) with a full‐width at half‐maximum (FWHM) of ≈2280 cm−1 (≈167 nm), and achieves a record EQE of 61.25% detected at 450 nm excitation through Li‐ion compensation. A prototype NIR pc‐LED is fabricated with MT:Cr3+, Li+ to evaluate its potential practical application, which reveals an NIR output power of 53.22 mW at a driving current of 100 mA, and a photoelectric conversion efficiency of 25.09% at 10 mA. This work provides an ultra‐efficient broadband NIR luminescent material, which shows great promise in practical applications and presents a novel option for the next‐generation high‐power compact NIR light sources.

Generally, crystal field engineering is an important means to regulate Cr3+ luminescence in near-infrared (NIR) phosphors. Host cation substitutions, including single substitutions, double substitutions, and even multiple substitutions, are widely used as a common means to modify the crystal field of Cr3+-activated phosphors. However, the tunable range using this strategy is usually limited because it is susceptible to the limitation of the host and its initial structure. In this work, we designed and synthesized a new type of controllable NIR-emitting phosphor Li2Mg3TiO6:Cr3+ using a new Cr3+ luminescent ion substitution strategy in which a double Cr3+ ion unit [Cr3+–Cr3+] was employed to replace a [Mg2+–Ti4+] unit to balance the charge. Just by changing the concentration of Cr3+, the NIR emission peak of the phosphor can be regularly adjusted from 720 to 920 nm, and the full width at half maximum reaches 258 nm. The internal quantum efficiency and external quantum efficiency of the Li2Mg3TiO6:0.03Cr3+ sample are measured to be 72.1 and 28.1%, respectively. An NIR phosphor-converted light-emitting diode (pc-LED) is fabricated by the LMT:Cr3+ phosphor and a blue chip, and the radiant fluxes of 31.09 mW@(3 V ∼ 100 mA) and 71.56 mW@(3 V ∼ 420 mA) are achieved. The results confirmed that the luminescence material has great application potential in the field of NIR spectroscopy.