Lanthanide-Based Metal–Organic Frameworks with Upconversion/Downshifting Emission for Optical Information Encryption

Lanthanide-based metal-organic frameworks (Ln-MOFs) are widely studied as downshifting luminescent materials. However, achieving lanthanide upconversion luminescence is still challenging in Ln-MOFs. Here, a new Yb-IPA MOF with upconversion luminescence at 498 nm was designed and synthesized using isophthalic acid (IPA) and Yb³⁺ salt. Under 980 nm excitation, the Yb-IPA MOFs emit the cyan light of Yb³⁺ ions through cooperative upconversion luminescence. Subsequently, Tb³⁺, Eu³⁺, and Ho³⁺ were doped into Yb-IPA MOFs, and the characteristic upconversion emissions of these lanthanide ions were successfully achieved in the corresponding codoped MOFs. These codoped MOFs showed downshifting and upconversion luminescence of lanthanide ions under ultraviolet and near-infrared light irradiation, respectively. The multimode-emission MOF system displays significant potential for applications in the field of information security, especially in the development of advanced optical anticounterfeiting and information encryption.