Structural Design for Controlling the Lattice Strain Relaxation Process in TiO2/SiO2 Core-Shell Nanoparticles

Substantial lattice strain arising from lattice misfit of the components of core-shell nanomaterials used to accommodate lanthanide emitters usually significantly results in an inhomogeneous shell, which substantially degrades the luminescence performance. We systematically studied the epitaxial habit, crystallization process, and interfacial energy transfer behavior of Tb3+- and Eu3+-doped TiO2/SiO2 multilayer core-shell and hollow multishell nanoparticles. The results demonstrate that lattice strain relaxation leads to shell reconstruction and the formation of interfacial defects and facilitates phase transformation for the first time. We also demonstrate that the lattice strain relaxation mode is determined by the structure. In particular, this is the first report of a unique shell reconstruction mode that decreases the size of C@SiO2@TiO2@SiO2 hollow triple-shell nanospheres with the consequent formation of wrinkles. By exploiting a rational structural design, the adverse effects of misfit strain can be minimized. Two types of "defect-free" interfaces and the resulting two types of interfacial energy transfer are integrated into one system, which are achieved by an alloyed interface and a sharp interface with high lattice strain. Our investigation on the strain relaxation process and the strain engineering approach is expected to shed more light on precise control of the fabrication and functionality of nanomaterials.