Anodic dc electrochemical luminescence (ECL) property of nondoped and rare earth (RE) ion-doped MgIn2O4 electrodes, famous as a transparent electronic conducting material, was investigated. Nondoped and Dy3+, Sm3+, Ho3+, Er3+, Eu3+, and Tm3+ doped MgIn2O4, usually exhibiting no or very weak photoluminescence (PL), showed ECL under anodic polarization over 20 V. ECL luminescence can be attributed to that from the oxygen defect for nondoped MgIn2O4 and to that from the doped emission centers (RE ions) for MgIn2O4: RE, respectively. Doped RE ions form solid solution within MgIn2O4 host. From the Rietveld refinement analysis of X-ray patterns, we concluded that RE ions are located at the 16d site in MgIn2O4. The ECL intensity dependence on the Er3+ ion concentration of MgIn2O4: Er3+ showed a maximum at [Er3+] = 2% and then decreased, whereas PL intensity monotonously increased with increasing Er3+ concentration. These results suggest that electron conductivity of MgIn2O4 host are also related with the ECL property. (c) 2006 The Electrochemical Society.