We have demonstrated electroswitchable emission and coloration using a novel composite material containing luminescent europium(III) complex Eu(hfa)₃(H₂O)₂ and diheptyl viologen HV²⁺. The photoluminescence of the Eu(III) complex was controlled by the electrochemical coloration of HV²⁺via intermolecular energy transfer mechanisms.

Electrochemical modulation of red luminescence from a europium(III) complex has been demonstrated. In order to elucidate the mechanism of luminescence modulation, its cyclic voltammogram, absorption spectra, emission spectra, emission lifetime, and emission quantum yield were measured. From these measurements, the modulation of emission was found to be achieved through an electrochemical reaction of TiO₂, which is facilitated by electron transfer between the europium(III) complex and TiO₂. Subsequent immobilization of the europium(III) complex on a TiO₂ electrode resulted in an on–off emission contrast of 74 : 1, with the response time and repetition stability of the emission switching being considerably improved.