Analysis of the Shell Thickness Distribution on NaYF₄/NaGdF₄ Core/Shell Nanocrystals by EELS and EDS

Abstract

The structure and chemical composition of the shell distribution on NaYF 4 /NaGdF 4 core/shell nanocrystals have been investigated with scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDS). The core and shell contrast in the high-angle annular dark-field (HAADF) images combined with the EELS and EDS signals indicate that Gd is indeed on the surface, but for many of the particles, the shell growth was anisotropic. SECTION Nanoparticles and Nanostructures

Impacts of core–shell structures on properties of lanthanide-based nanocrystals: crystal phase, lattice strain, downconversion, upconversion and energy transfer

“…1c. 36 They also fabricated Eu 3+ -doped LnF 3 core-shell nanoparticles with the incorporation of Eu 3+ ions in the core. The shell surface was functionalized with citrate ligands to stabilize the particles from aggregation in aqueous solution and for better dispersibility.…”

An Upconversion Nanoparticle with Orthogonal Emissions Using Dual NIR Excitations for Controlled Two‐Way Photoswitching

“…The shape evolution phenomena during the shell growth of the nanoparticles were ascribed to the kinetically favored anisotropic shell growth during the coating process, which was also observed by other groups. [8i, 10] The High-resolution TEM (HRTEM) image shown in Figure 1f reveals the (100) crystallographic planes of the Tm@Er UCNPs and demonstrates that the as-synthesized multishell UCNPs were single hexagonal phase crystals. Additionally, the energy-dispersive X-ray spectroscopy (EDX) spectrum indicates the presence of the elements Na, F, Y, Yb, Nd, Er, and Tm, which confirms the composition of the nanoparticles (see Supporting Information, Figure S2).…”

Intrinsic single-band upconversion emission in colloidal Yb/Er(Tm):Na3Zr(Hf)F7 nanocrystals

“…Moreover, due to the large cation radii difference for Ln 3+ and Zr 4+ , introducing Ln 3+ ions into the Na 3 ZrF 7 lattice also results in severe structural inhomogeneity, i.e., generates Ln 3+ clusters, which has already been reported in the Ln:NaREF 4 (RE = Y, Sc) NCs. 23,24 The formation of Ln 3+ clusters greatly shortens the distances between Ln 3+ (Ln = Yb, Er, Tm) dopants. As a result, the short distances between Yb 3+ and Er 3+ (Tm 3+ ) help to populate the meta-stable excited states of Er 3+ (Tm 3+ ) remarkably, and the close distribution of Er 3+ (Tm 3+ ) benefits to enhancing the cross-relaxation (CR) between Er 3+ and Er 3+ (or Tm 3+ and Tm 3+ ) ions.…”