Electrofluorochromism based on the valence change of europium complexes in electrochemical devices with Prussian blue as the counter electrode

Abstract

The electrofluorochromism of Eu complexes based on the valence change between Eu³⁺ and Eu²⁺ is demonstrated in a two-electrode electrochemical device consisting of Prussian blue (PB) as the counter electrode. This study aims to improve the electrofluorochromic (EFC) performance of luminescence switching between Eu³⁺ and Eu²⁺ by enhancing the electrochemical reactivity of the EFC device. By introducing a PB film as a counter electrode in a two-electrode device, the redox reaction of Eu^3+/2+ is promoted because of charge compensation by the counter PB film. The increase in the reaction charge enables faster changes in the photoluminescence from Eu³⁺ to Eu²⁺ and an increase in the blue luminescence intensity from the Eu²⁺ state. This approach achieves a lowered driving voltage, accelerates the electrochemical redox reaction of the Eu complex, and enhances the reversibility of the valence change of the Eu ion.