Hedgehog-Like Upconversion Crystals: Controlled Growth and Molecular Sensing at Single-Particle Level.

Topological control of nanostructures plays a crucial role in understanding the crystal growth process at the nanometer length scale. Here, the scalable synthesis of upconversion materials with distinct hedgehog-like morphologies by a seed-mediated synthetic procedure is reported. It is demonstrated that a close match in the crystal lattice between the core and shell components is essential for synthesizing such hierarchical nanostructures. These optical nanomaterials also enable the development of a single-particle-based platform for high-sensitivity molecular sensing.