Design a rare-earth free broadband NIR phosphor and improve the photoluminescence intensity by alkali charge compensation

Abstract Near-infrared (NIR) phosphors, promising non-destructive measurement materials for food, have attracted extensive attention worldwide. Herein, we designed a low-cost rare-earth free Mg2B2O5:Cr3+ phosphor. Under the excitation of 450 nm, the Mg2B2O5:Cr3+ phosphors show a broadband near-infrared emission at 800 nm, for 4T2 (4F) → 4A2 transition. The optimal concentration of Cr3+ was about 0.003 and a higher concentration will lead to concentration quenching owing to dipole-dipole interaction. Moreover, considering the unequal substitution of Mg2+ by Cr3+, charge compensation had been applied to improve the photoluminescence. The mechanism of alkali charge compensation and its effect on polyhedron distortion had been illustrated. The relationship between decay lifetime and charge compensation had been discussed. Finally, the activation energy for thermal quenching of as-prepared samples was calculated. The increasing polyhedron distortion result in worse thermal stability, which was explained by the configurational coordinate model. The above results are helpful in the development of low-cost near-infrared phosphors and the enhancement of photoluminescence intensity.