3D Photonic Metacrystals with Enhanced Collective Mie Resonances for Dual Structural Coloration

3D photonic crystals offer nonfading structural coloration and complex optical properties through coupled Mie resonances in high-refractive-index materials. Although strong magnetic resonances make them promising, they often suffer from optical losses in the visible spectrum. Enhancing Mie resonances and quality factors through collective coupling in lithographically ordered arrays has been demonstrated. However, large-area applications using self-assembled colloidal resonators in metafluid inks have been limited by inadequate monodispersity and insufficient surface charge, hindering effective ordering. Here, we report high-quality 3D Mie-resonant metacrystals formed by high-temperature self-assembly of CdS nanoparticles (refractive index 2.5). Their long-range ordering attenuates local density of states overlapping with Mie resonances, minimizing external radiation losses and yielding one order of magnitude enhancement in collective Mie behavior. A 13-fold enhancement in magnetic Mie resonances with quality factors reaching 17 is experimentally demonstrated. The structures produce Bragg peaks that coexist with enhanced collective Mie resonances, enabling angle-dependent, dual nonfading structural coloration across the visible and near-infrared spectrum. As a proof of concept, wafer-scale inkjet printing using metafluid inks of CdS and ZnS nanoparticles demonstrates stable coloration and angle-sensitive hues. This work opens new avenues in durable structural coloration and multifunctional optical platforms for applications such as ultrasensitive polarimetry and advanced optical sensing.