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 cm(2) 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. (C) 2018 Elsevier Ltd. All rights reserved.