Ln(3+)-doped nanoparticles for upconversion and magnetic resonance imaging: some critical notes on recent progress and some aspects to be considered.

In this feature article we will critically discuss the synthesis and characterisation aspects of Ln(3+)-doped nanoparticles (NPs) that show upconversion, upon 980 nm excitation. Upconversion is a non-linear process that converts two or more low-energy photons, often near-infrared photons, into one of higher energy, e.g.

Self-focusing by Ostwald ripening: a strategy for layer-by-layer epitaxial growth on upconverting nanocrystals.

We demonstrate a novel epitaxial layer-by-layer growth on upconverting NaYF(4) nanocrystals (NCs) utilizing Ostwald ripening dynamics tunable both in thickness and composition. Injection of small sacrificial NCs (SNCs) as shell precursors into larger core NCs results in the rapid dissolution of the SNCs and their deposition onto the larger core NCs to yield core-shell structured NCs. Exploiting this NC size dependent dissolution/growth, the shell thickness can be controlled either by manipulating the number of SNCs injected or by successive injection of SNCs.

The unexpected structures of "core-shell" and "alloy" LnF3 nanoparticles as examined by variable energy X-ray photo-electron spectroscopy.

Lanthanide fluoride nanoparticles were synthesized in aqueous media using procedures intended for a core-shell structure of Ln((1))F(3)-Ln((2))F(3), its reverse architecture, and an alloy structure. Their structures were examined by variable photon energy photo-electron spectroscopy using synchrotron radiation, along with X-ray powder diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and luminescence spectroscopy. The results show that the nanoparticles intended for a core-shell structure do not have a core-shell structure, and that nanoparticles intended for an alloy structure do not always have an alloy structure.

Cation exchange in lanthanide fluoride nanoparticles.

Cation exchange in lanthanide fluoride nanoparticles is reported. Typically, dispersible LnF(3) nanoparticles were exposed to another lanthanide ion that was roughly 5 times the amount of Ln(3+) in the nanoparticles. Results show that cation exchange of GdF(3) nanoparticles with La(3+) was almost complete in 1 min, and it also happens reversibly although the degree of exchange is not as much as the forward reaction.

Preparation of PVA/PEI ultra-fine fibers and their composite membrane with PLA by electrospinning.

Ultra-fine fibers of poly(vinyl alcohol)/polyethylenimine (PVA/PEI) were prepared by electrospinning of their blend solutions in water. Effects of PVA/PEI mass ratio and the polymer concentration on the fiber morphology were discussed by analysis of scanning electron micrographs. Results showed that uniform ultra-fine fibers could be obtained from an 8% PVA/PEI solution with 75:25 mass ratio.

[Electrospinning and morphology of ultrafine poly (D, L-lactide) fibers].

Ultrafine poly (D, L-lactide) (PLA) fibers with diameter less than 200 nm produced by electrospinning were studied to obtain tissue restoration resembling extracellular matrix. Scanning electron microscopy was used to observe the fiber morphology. Results showed that the solvent was the critical factor to determine the formation of the electrospun PLA fibers.

Electrospinning of chitosan solutions in acetic acid with poly(ethylene oxide).

Electrospinning of chitosan solutions with poly(ethylene oxide) (PEO) in an aqueous solution of 2 wt% acetic acid was studied. The properties of the chitosan/PEO solutions, including conductivity, surface tension and viscosity, were measured. Morphology of the electrospun chitosan/PEO was observed by using scanning electron micrographs.