Fine-Tuning of Near-Infrared Emission in Fe-Activated Spinel Phosphors via the Synergistic Effect of Sites Inversion and Atomic Disorder

Achieving continuous tunability, high efficiency, and outstanding thermal stability of near-infrared (NIR) phosphors remains challenging for optoelectronic device fields. To address this issue, a strategy is proposed based on the substitution of both cations and anions in the intermediate spinel structure, which successfully achieved fine-tuning of NIR emission of Mg_1+yGa_2-yO_4-yF_y:Fe³⁺ phosphors with prominent optical characteristics. The NIR emission contains new luminescent centers with random O/F coordination and is successfully constructed. This co-substitution promotes further inversion of the cationic sites and induces atomic disorder, changing the crystal coordination environment and making Fe³⁺ breakthrough the Laporte selection rule, enabling fine-tuning of Fe³⁺ emissions in the range of 707–740 nm and broadening of the full width at half maximum by 30 nm. Moreover, the Mg_1.15Ga_1.85O_3.85F_0.15:Fe³⁺ phosphor reached a high quantum yield of 71.6% and presented excellent thermal stability with an emission intensity retention of 81% at 493 K. The emission of the fabricated NIR phosphor-converted light-emitting diodes also matched well with the photosensitive pigment P_fr, demonstrating its feasibility for plant growth lighting applications.