Self-Assembly of Heterogeneous Structured Rare-Earth Nanocrystals Controlled by Selective Crystal Etching and Growth for Optical Encoding

Programmatically assembling inorganic nanocrystals (NCs) into long-range-ordered superstructures has been well-documented as a theme to construct novel materials with unique properties. Herein, one-dimensional oriented self-assembly of core–shell structured rare-earth doped β-NaREF4 NCs is reported. In the epitaxial growth process, β-NaREF4 crystals featuring larger negative lattice mismatch usually exhibited longitudinal growth preference. In this case, the lateral crystal of the hexagonal prisms would be etched by OA– ions along the direction parallel to the (001) facets. This anisotropic morphology evolution can lead to the anisotropic noncovalent interactions between long-chain alkyls of oleic acid molecules and contribute to the oriented self-assembly in the ⟨001⟩ direction. On the basis of the studies on the heterogeneous NC self-assembly, a rare-earth nanohybrid assembly is further prepared by functionalizing the NC surface with a pH-responsive ligand N-(2-pyridinyl)benzoylacetamide (HPBA), and this nanohybrid self-assembly exhibits great potential in spatial–temporal dimensional optical encoding. This study provides a novel strategy based on selective crystal etching and epitaxial growth for oriented self-assembly of NCs and represents an important step toward the design of well-defined superstructures with unique properties.