Electrochemiluminescent modulation: Electrochemiluminescence (ECL) of CdS nanocrystal (NC) film-Au nanoparticle (NP) integrated system is controllably quenched by magnetic Co2+ ions without external magnetic field owing to spin-polarized modulation of the electron-hole recombination caused by ferromagnetic alignment of Co2+ in close proximity to Au NPs. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.