Bridging the Gap Between NIR‐I and NIR‐II Bands via Efficient Cr ³⁺ →Ni ²⁺ Energy Transfer in Superstoichiometric MgO· <i>n</i> Ga ₂ O ₃ ( <i>n</i> &gt; 1) Spinels

ABSTRACT 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 &gt; 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.