Bridging the Gap Between NIR-I and NIR-II Bands via Efficient Cr3+→Ni2+ Energy Transfer in Superstoichiometric MgO·nGa2O3 (n > 1) Spinels

Cr 3+ emission can well cover the NIR-I region (700–950 nm), while Ni 2+ emission typically extends across the NIR-II region (1000–1700 nm), making the Cr 3+ –Ni 2+ co-doped phosphors among the most promising ultrabroadband NIR emitters for phosphor-converted light-emitting diodes (pc-LEDs). However, a pronounced gap or even spectral discontinuity between the two emission bands results in a severely imbalanced photon flux across the spectrum, thereby degrading multicomponent spectral detection accuracy and significantly limiting the practical applications of such NIR pc-LED devices. Here, we report a superstoichiometric spinel MgO· n Ga 2 O 3 :Cr 3+ ,Ni 2+ ( n > 1) phosphor, in which the excess Ga 2 O 3 increases the degree of cation inversion to achieve a long-wavelength Cr 3+ emission at 895 nm, substantially elevating the spectral gap height to a state-of-the-art value of ≈36%. Moreover, efficient energy transfer from Cr 3+ to Ni 2+ enables the optimized MgO·1.2Ga 2 O 3 :Cr 3+ ,Ni 2+ phosphor to demonstrate a high internal quantum efficiency of 97% and excellent thermal stability. Finally, the as-fabricated NIR pc-LED delivers an exceptional photoelectric efficiency of 21% at 20 mA and a maximum NIR output power of 62 mW at 350 mA. This work establishes a new pathway toward next-generation compact ultrabroadband NIR pc-LEDs featuring unprecedented spectral flatness and superior optoelectronic performance.