A bottom-up route to tunable nanophotonic materials via binary nanocrystal co-assembly

The self-assembly of nanocrystals into ordered hierarchical structures offers a powerful way to engineer emergent optical properties. In this study, we demonstrate a straightforward, bottom-up co-assembly of cerium oxide (CeO 2 ) and gold (Au) nanocrystals (NCs) into binary arrangements that enhance fluorescence via plasmon-exciton coupling. By systematically varying the Au-NCs concentration, we identify an optimal doping level at 1.6 mol% Au where the emergence of ordered domains with Frank-Kasper structural motifs coincides with a 15-fold enhancement in fluorescence emission measured relative to the baseline integrated emission of the disordered CeO 2 -NCs aggregates. This amplification is driven by the creation of intense near-field electromagnetic hotspots from the Au-NCs’ localised surface plasmon resonance (LSPR), whose effect is maximised within this specific, locally ordered architecture. Conversely, excessive doping (3.0 mol% Au) results in a loss of optical performance due to phase segregation and disruption of this critical ordering. This work establishes a direct correlation between the NCs concentration, the spontaneous formation of complex ordered domains, and the resulting collective optical properties, demonstrating a simple yet effective pathway for creating tunable nanophotonic materials. • A simple bottom-up route to create tunable nanophotonic materials • 500% fluorescence boost at 1.6 mol% Au via ordered nanocrystal domains • Plasmon-exciton coupling is optimised in Frank-Kasper architectures • Structural order drives plasmonic enhancement; disorder reduces effect • Direct link shown between dopant level, structural order, and optical output