Single-band near-infrared upconversion emission and visible-light absorption in highly doped pseudo-perovskite oxides

Currently, concentration-induced near-infrared upconversion quenching at highly doped levels of lanthanide ions poses a significant constraint for their practical applications. In this work, the fabricated Tm3+/Yb3+ codoped Na(0.5)Bi(2.5)Nb(2)o(9) (NBN) materials with a layered structure exhibited a single-band near-infrared to near-infrared upconversion emission (808 nm emission, 980 nm excitation) with no obvious concentration quenching even with a higher Yb3+ content of 90 mol%, while maintaining excellent thermal stability. Meanwhile, the Tm3+/Yb3+ co-doped NBN materials showed strong visible-light absorption at 400-800 nm under the irradiation with sunlight (AM1.5), and the absorbed light can be released via a thermal stimulus, showing a typical photochromic reaction. The near-infrared upconversion emission intensity was effectively tuned after and before sunlight irradiation. This research provides a new strategy for designing high-efficiency near-infrared upconversion and visible photoresponsive oxides for near-infrared modulation, solar energy conversion, and other multifunctional applications.