Lanthanide “Chameleon” Multistage Anti‐Counterfeit Materials

• Published in: Advanced functional materials Vol. 27; no. 20
• Main Authors: Kaczmarek, Anna M., Liu, Ying‐Ya, Wang, Chunhua, Laforce, Brecht, Vincze, Laszlo, Van Der Voort, Pascal, Van Hecke, Kristof, Van Deun, Rik
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 25.05.2017
• Subjects: anti‐counterfeiting; Counterfeit; Counterfeiting; Lanthanides; Luminescence; Materials science; Materials selection; metal–organic frameworks; Multistage; Optical properties; security technologies; temperature dependent luminescence
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201700258

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 β‐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 β‐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. Hybrid lanthanide/metal–organic‐framework materials for application in multistage security technologies are proposed. These materials show both wavelength‐ and temperature‐dependent luminescence properties. They exhibit “chameleon” behavior by changing their emission color in response to changes in the environment. For this application, the combination of Tb3+/Sm3+ is superior to that of Tb3+/Eu3+, which is most often investigated for temperature‐dependent luminescence.