Highly tunable superparamagnetic colloidal photonic crystals

(Figure Presented) Tuning crystal: Superparamagnetic nanocrystal clusters can self-assemble into colloidal photonic crystals in solution, whose stop bands can be magnetically tuned across the entire visible spectrum. Owing to the high magnetization and the highly charged polyacrylate-capped surface of each cluster, the colloidal photonic crystals show a rapid, reversible, and widely tunable optical response to external magnetic fields.