Kinetically Determined Crystal Structures of Undoped and La³⁺-Doped LnF₃

Abstract

A series of lanthanide fluoride nanoparticles were prepared with a simple colloidal approach at 75 °C. All the nanoparticles are highly water-dispersible with sizes in the range of 3−10 nm. The light lanthanide fluoride salts, LaF3, CeF3, and NdF3, have the same trigonal crystal structure as the corresponding bulk materials. However, for the fluoride salts of the heavy Dy, Ho, Er, and Yb, nonstoichiometric cubic structures of Na x Ln y F z composition were identified. Particularly, the middle GdF3 and EuF3 nanoparticles have both trigonal and orthorhombic crystal phases instead of a single orthorhombic phase as for the corresponding bulk materials, which is attributed to kinetically formed products. Study of La3+-doped GdF3 nanoparticles showed that 15% La3+ doping is sufficient for GdF3 nanoparticles to crystallize completely in the trigonal phase, i.e., the same as LaF3, which is dramatically different than 50% La3+ doping for the bulk. Finally, on the basis of the thermodynamic cycle for the preparation of the doped materials, calculations carried out explain well the published experimental results for the bulk. However, this approach failed to explain the results of the nanoparticles. Evidence is provided that the formation of kinetic products is responsible.

Dopant-controlled synthesis of water-soluble hexagonal NaYF4 nanorods with efficient upconversion fluorescence for multicolor bioimaging

“…Very recently, van Veggel et al observed a similar doping effect in GdF 3 :La NCs. In their study, it was found that 15% La could induce a complete orthorhombic to trigonal phase transition of the GdF 3 :La NCs, however, the shape and size of the crystals were almost the same as the undoped GdF 3 NCs [48]. More interestingly, the doping effect on the anisotropic crystal growth is also suitable for other NaREF 4 host materials in our reaction system.…”

“…In 1991, Blasse et al observed that 50% La doping could induce a complete trigonal to orthorhombic phase transition in bulk GdF 3 crystals [47]. Very recently, van Veggel et al found that undoped GdF 3 NCs were formed as a mixture of trigonal and orthorhombic phases, and 15% La doping was sufficient for them to crystallize completely in the trigonal phase [48]. However, the dopant-controlled cubic-tohexagonal phase transition in the RE fluoride NCs has not been reported so far.…”

Time‐Resolved FRET Biosensor Based on Amine‐Functionalized Lanthanide‐Doped NaYF4 Nanocrystals

“…[12] Transmission electron microscopy (TEM) images showed that the as-prepared NCs are roughly spherical with a size distribution ranging from 20 to 40 nm ( Figure S1, Supporting Information). Clear lattice fringes observed in the high-resolution TEM (HRTEM) image ( Figure S1) reveal high crystallinity of the NCs.…”

Chemical modification of the surface of highly dispersed metal salt crystals

“…The following acids and their salts are most often used as modifiers in both protonated forms: citric [3][4][5][6][7][8][9][10][11], oleic [12][13][14][15][16][17][18][19][20][21][22][23], alkane [14,20,21,24,25], aro matic [20,26], and derivatives of phosphorous con taining acids [4,7,[26][27][28][29][30][31][32][33].…”