Er³⁺-Sensitized Upconversion/Down-Shifting Luminescence in Metal-Organic Frameworks

Photoluminescent metal-organic frameworks (MOFs) are used as optical materials with excellent properties, of which the lanthanide-doped MOFs are able to emit in a broad region from visible to near-infrared due to their unique 4f-orbital electronic structure. Herein, Er³⁺ and Y³⁺ ions are selected as the metal centers of the MOFs and Er³⁺ is used as a sensitizer to absorb 980 nm excitation light. At the same time, Er³⁺ ions also act as activators that emit upconverting visible light and down-shifting near-infrared light. In addition, Tm³⁺, Ho³⁺, and Eu³⁺ ions were individually doped into the Er³⁺-doped MOFs to investigate the variation of energy-transfer paths in the presence of different lanthanide activators. Finally, the pathway of energy transfer in these Er³⁺-sensitized luminescent-MOFs was summarized. This work provides new insights for further development of both upconversion and down-shifting luminescence of MOFs.