Colloidal clusters of icosahedrons and face-centred cubes

Synthetically colloidal clusters with new functions and well-controlled size distribution can in principle be constructed using colloidal particles. The building units could be integrated into dense-packed and desired structured with novel functions by means of an efficient strategy or binding patterns. Here we synthesized colloidal clusters of icosahedrons and long-range ordered face-centered cubes (FCCs) via emulsion self-assembly using fluorescence upconversion nanoparticles NaGdF₄: Yb³⁺, Er³⁺ as building blocks. The icosahedrons and FCCs structure may generate spontaneously due to an entropy-driven process. The morphology and structure of colloidal clusters have noticeable transformation from icosahedron-like symmetry to FCC symmetry with the increasing size of clusters. Furthermore, the colloidal clusters could be decorated with cationic polyethyleneimine (PEI) via electrostatic interaction. When copper ions are added, the amino groups of PEI could coordinate with Cu²⁺ forming low toxic PEI-Cu²⁺ layers, which can further serve as energy receptors to quench upconversion fluorescence with 980 nm laser excitation. Our results reflect that the colloidal clusters not only can serve as a fluorescence platform of detection and analysis but also may represent advancement in the field of colloidal and interface sciences.