Electro-generated chemiluminescence (ECL) has attracted increasing attention as a new platform for light-emitting devices; in particular, the use of mechanically stretchable ECL gels opens up the opportunity to achieve deformable displays. The movements of radical ions under an external electric field include short-range diffusion near the electrodes and long-distance migration between the electrodes. So far, only the diffusion of radical ions has been considered as the operating principle behind ECL. In this study, electrochemical and optical analysis was performed systematically to investigate the role of ion migration in ECL devices. This study reveals that long-distance migration of radical ions can be a key variable in ECL at low frequencies and that this effect depends on the type of ion species and the operating conditions (e.g. voltage and frequency). We also report that the emissions from the two electrodes are not identical, and the emission behaviors are different in the optimal operating conditions for the red, green, and blue ECL emissions.