A molecule of luminol bound as guest inside a Co8 coordination cage host undergoes oxidation by H2O2 to generate chemiluminescence by a process in which the Co(II) ions in the cage superstructure activate the H2O2: accordingly the cage not only co-locates the reactants but also acts as a redox partner in the catalysis. The luminescence from oxidation of the cavity-bound luminol can transfer its excitation energy to surface-bound fluorescein molecules in an unusual example of Chemiluminescence Resonance Energy Transfer (CRET).