Tunable Cr3+-Cr3+ ion pair luminescence properties of MgGa2O4:Cr3+ NIR phosphors via alkaline-earth metal co-doping

The Cr³⁺-Cr³⁺ ion pair has emerged as a highly efficient near-infrared (NIR) luminescence center with improved thermal stability and broader short-wave-infrared (SWIR) bandwidth compared to isolated Cr³⁺ ions. However, its formation typically requires high Cr³⁺ concentrations, which may induce concentration quenching. Herein, we propose an atomic substitution strategy to regulate Cr³⁺-Cr³⁺ pair formation without relying on excessive Cr³⁺ doping. Using MgGa₂O₄: Cr³⁺ as a model system, density functional theory (DFT) calculations combined with experimental analysis reveal that substituting tetrahedral Mg sites with alkaline earth metals influences Cr³⁺-Cr³⁺ ion pair formation. A larger ionic radius at the Mg site facilitates easier formation of Cr³⁺-Cr³⁺ ion pairs. By introducing Be, Ca, Sr, or Ba, we successfully controlled the population of Cr³⁺-Cr³⁺ pair centers, tuning SWIR emission intensity between 800 and 1200 nm. This work deepens understanding of Cr³⁺-Cr³⁺ ion center formation and offers a new route to tailor SWIR luminescence.