The electrochemical preparation of europium doped zinc oxide and europium oxide/hydroxide as thin films is investigated. First, a thermodynamic study of the Eu-Cl-H2O system has been carried out at 25 and 70 degrees C in order to predict the electrochemical behaviour of Eu(III) dissolved in aqueous solution containing chloride ions. A comparison of the Eu-Cl-H2O and Zn-0-1120 Systems indicates the possible coprecipitation of ZnO and Eu(OH)3 from deposition solutions containing well-adjusted Eu(III)/Zn(II) concentrations ratio. The thermodynamic predictions have been confirmed experimentally by the electrochemical co-deposition of ZnO/Eu thin films on conducting electrode substrates at -1.4V versus MSE. The presence of europium in the film is detected for Eu(III)/Zn(II) concentration ratio at (0.6 mM/5 mM) which is lower than the predicted value. Increasing Eu(III) concentration leads to the rapid appearance of two phases: dispersed zinc oxide nanorods and, at the bottom of the rods, a covering layer containing Eu(OH)3 and zinc. The density of ZnO rods decreases and the rod size increases with increasing Eu(III) concentration in the bath. Above I mM EuCl3, a dramatic fall in the current density is observed with the formation of a less conducting ZnO/Eu mixed deposit. (C) 2007 Elsevier Ltd. All rights reserved.