Tailoring spin-paired Cr3+ dimers in a spinel host for giant-tunable and enhanced near-infrared emission

Abstract

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 LiZn_0.6Mg_0.4SbO₄ host to achieve extended broadband NIR emission. Heavy Cr³⁺ doping, by 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. An NIR phosphor-converted light-emitting diode (pc-LED) was fabricated and it delivered 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.