Potential End-Use of a Europium Binary Photoluminescent Ink for Anti-Counterfeiting Security Documents

Composed of two europium complexes doped in polyvinyl butyral as the host material, a novel photoluminescent ink has been formulated by synthesizing Eu(FAC)₃Phen as a red luminescent down-shifting emitter and employing SrAl₂O₄:Eu, Dy as a long persistent green phosphor. Both emitters are incorporated to design a photoluminescent ink with binary emission under a single UV excitation wavelength, where a red light is emitted when exposed under 325 nm, subsequently becoming green upon the UV light being switched off. The concept presented here is unequivocally distinct from the classical dual-mode emission, which requires a second extra near-infrared excitation around 980 nm to produce a binary luminescence. This work demonstrates the effortlessness of using one UV excitation for dual-mode visible emission while rendering the counterfeiting of confidential documents more onerous.