Lanthanide "Chameleon" Multistage Anti-Counterfeit Materials

Hybrid materials displaying multistage security behavior, where a single material shows both wavelength-and temperature-dependent luminescence properties, are reported. The materials consist of mixed-lanthanide beta-diketonate complexes grafted into the pores of a nanosized 2,2'-bipyridine-5,5'-dicarboxylate-acid MOF. A very specific choice of lanthanides and their ratios, as well as beta-diketonate ligand, is crucial for obtaining the desired properties. The wavelength-dependent luminescence properties of the materials are very well matched with the excitation wavelengths of a standard UV lamp, and a clearly visible change in luminescence is observed in a narrow temperature range (slightly below and above room temperature), proving them to be excellent materials for use in anti-counterfeit technologies, which would be almost impossible to mimic.