Effect of pH on the electrochromic and photoluminescent properties of Eu doped WO3 film

Highlights: • Eu doped WO₃ film exhibits dual function of electrochromic switching and red emission. • Effect of pH on electrochromic and photoluminescent performances of Eu doped WO₃ film was first systematically investigated. • Eu doped WO₃ film achieves optimal coloration and transmission modulation of 70.1% (680 nm) at pH 2.2. • Eu doped WO₃ film exhibits a tunable red emission as a response to the applied electric field. • The intensity of red emission could be enhanced by increasing pH of precursor solution. Eu ions doped WO₃ (Eu-WO₃) film is demonstrated to possess electrochromic switching and tunable red emission. The effect of pH on structure, morphology, electrochromic and photoluminescent performances of Eu-WO₃ film, prepared by hydrothermal method, has been systematically investigated for the first time in this work. We found that as pH increases, a new phase of monoclinic W₁₇O₄₇ crystal and an open porous morphology appear. Electrochromic and photoluminescent properties of Eu-WO₃ film could be modulated by tuning pH. On one hand, Eu-WO₃ film achieves the maximum transmission modulation of 70.1% and high coloration efficiency of about 55.95 cm² C⁻¹ (680 nm) at pH 2.2. On the other hand, red emission of Eu-WO₃ film is tunable as a response to external potential and its intensity is proved to be enhanced by increasing pH.