Reversible Thermo/hydrochromic Luminescence in a Ln-MOF Film for Anticounterfeiting Application

Stimuli-responsive luminescent materials have attracted much attention in anticounterfeiting applications due to their excellent optical encryption capabilities. Here, a dual-stimuli-responsive lanthanide metal–organic framework (Tb/Eu-MOF) film is presented to enrich luminescence response behaviors for advancing the security levels. The loss/gain of H2O ligands under the stimulation of heat/moisture drives the reversible phase transformation of Ln-MOF films between two phases with distinct ionic distances. The shortening of the ionic distance upon heating facilitates Tb3+-to-Eu3+ energy transfer, leading to an emission color change from green to red. The opposite influence brought by moisture reverses the emission color back to green. We show that the color response of the Ln-MOF films can be deliberately controlled by rational design of the MOF structure and stimulation parameter for high-security anticounterfeiting applications.