Tailoring Spin-Paired Cr3+ Dimers in a Spinel Host for Giant-Tunable and Enhanced Near-Infrared Emission

Broadband near-infrared (NIR) phosphors activated by Cr3+ are pivotal for next-generation NIR light sources, yet achieving long-wavelength NIR emission remains challenging. Herein, we report a strategy of tailoring spin-paired Cr3+ ion dimers in a spinel-type LiZn0.6Mg0.4SbO4 host to achieve extended broadband NIR emission. Heavy Cr3+ doping, inducing spin-paired Cr3+ ion dimers, coupled with crystal-field engineering shifts the original 709 nm narrow-band emission to 860 nm (via Mg2+ incorporation) and further to 970 nm broadband emission (via Ca2+ incorporation). The optimized phosphor exhibits a 1.8-fold enhancement in thermal stability and a 1.35-fold increase in internal quantum efficiency compared to its Mg-free counterpart. Fabricated NIR phosphor-converted light-emitting diode (pc-LED) delivers an output power of 40.97 mW at 750 mA, demonstrating promising potential in versatile photonics applications. This work provides a viable approach for designing broadband NIR phosphors through precise manipulation of exchange-coupled Cr3+ ion dimers.