Heterometallic rare-earth metal–organic frameworks based on nonanuclear metal clusters were implemented as highly intricate optical tags, as described by Dorina F. Sava Gallis and co-workers in their Research Article on page 1203. Subtle compositional changes have a pronounced effect on intermetallic energy transfer, and thus on the resulting photophysical properties. Concomitant multi-emissive spectra and luminescence lifetimes result in tags with both overt (visible) and covert (near-infrared) properties, authenticated using orthogonal detection methodologies.