Accurate Control Of Core-Shell Upconversion Nanoparticles Through Anisotropic Strain Engineering

The effect of anisotropic interfacial strain on epitaxial growth and optical emission of sodium rare-earth fluoride core-shell nanoparticles is investigated. A variety of sodium rare-earth fluoride shells are grown on hexagonal-phase NaYF4:Yb/Er core for providing anisotropic tuning of interfacial strains. Using high-resolution transmission electron microscopy and X-ray diffraction characterizations, the correlations between the epitaxial habits and the interfacial strains are quantitatively addressed. Furthermore, the growth affinity is tuned by controlling precursor concentration in conjunction with Ca2+ doping, which results in accurate regulation of the anisotropic growth. The lattice strain resulting from mismatched epitaxy is found to enhance luminescence response of the nanoparticles to temperature change.