Scalable, Highly Uniform, and Robust Colloidal Mie Resonators for All-Dielectric Soft Meta-Optics

All-dielectric nanoparticles (NPs) with high (>3.0) or moderate (1.7-3.0) refractive indices have become fundamental to meta-optics, as they enable low-loss, low-heating, and quenching-free magnetodielectric Mie resonances, which are difficult to achieve by use of plasmonic counterparts. However, a scalable and versatile synthetic route for such magnetodielectric NPs retaining high uniformity, roundness, and robustness has remained elusive. Thus, soft self-assembly still represents an underutilized method in the optical engineer's toolset, which in turn limits the accessible range of meta-optics. Herein, a gram-scale and versatile synthesis of dielectric colloidal Mie resonators is presented, in which selenous acid precursors are converted into highly uniform, crystalline colloids by a low demand reaction. These crystalline selenium (c-Se) colloids enable strong electric and magnetic resonances due to their moderate refractive index (2.8-3.2 at optical frequencies), while simultaneously satisfying the requirements of high uniformity, roundness, and robustness. Even with these exotic properties, c-Se colloids are successfully self-assembled into various all-dielectric meta-optics systems including (i) metafluids exhibiting directional scattering, (ii) metamolecules with nanogap-dielectric resonances, and (iii) metacrystals with magnetodielectric bandgaps. The design space of all-dielectric meta-optics will be greatly expanded by utilizing soft self-assembly of c-Se colloids.