3D superlattices of fluorescent gold nanoparticles are prepared at an air/water interface. The hexagonal assembly extends over several micrometers, and crystals of triangular morphology are imaged using the fluorescence emission of the monolayers protecting the nanoparticles (see figure). Surprisingly, the superlattices are fluorescent even though the fluorescein derivative is close to the metallic core and strong quenching is expected.