Issue 45, 2020

Water dispersible ligand-free rare earth fluoride nanoparticles: water transfer versus NaREF4-to-REF3 phase transformation

Abstract

The chemical stability of oleate-capped sub-10 nm α- and β-NaREF4 NPs (RE = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu for α- and RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy for β-phase NPs) was evaluated under the acidic conditions used for ligand removal towards water dispersibility. It was found that for such small NPs, a pH lower than 3 was necessary for the water transfer to be efficient and to yield well-dispersed ligand-free NPs. In stark contrast to the generally considered good chemical stability of NaREF4, these conditions were observed to pose a risk to phase transformation of the NaREF4 NPs into much larger, hexagonal- or orthorhombic-phase REF3, depending on the NP composition. A correlation between the thermodynamic stability of the α/β-NaREF4 and the hexagonal/orthorhombic REF3 phases – dictated by the RE ion choice – and the chemical stability of the NPs was found. For instance, β-NaGdF4 NPs remained stable, while α-NaGdF4 NPs underwent phase transformation into hexagonal GdF3. More general, NaREF4 NPs based on lighter RE ions were more prone towards phase transformation, while those based on heavier RE ions exhibited stability. Herein, within the RE series, the borderline for phase transformation was identified as Tb/Dy for α-NaREF4 NPs and Sm/Eu for β-NaREF4 NPs, respectively. Also, given the large interest in luminescent NPs for, e.g. biomedical applications, optically active Ln3+ ions (Ln = Nd, Eu, Tb, Er/Yb) were doped into α/β-NaGdF4 host NPs, and the dopant influence on the chemical stability was evaluated. Steady state and time-resolved spectroscopy unveiled spectral features characteristic for Ln3+ f–f transitions, i.e. downshifting and upconversion, before and after ligand removal. Overall, the results herein described emphasise the importance of minding the chemical procedure used for ligand removal of NaREF4 NPs of different crystalline phases and RE compositions.

Graphical abstract: Water dispersible ligand-free rare earth fluoride nanoparticles: water transfer versus NaREF4-to-REF3 phase transformation

Supplementary files

Article information

Article type
Paper
Submitted
22 mar 2020
Accepted
18 apr 2020
First published
20 apr 2020

Dalton Trans., 2020,49, 16204-16216

Water dispersible ligand-free rare earth fluoride nanoparticles: water transfer versus NaREF4-to-REF3 phase transformation

N. Liu, N. Gobeil, P. Evers, I. Gessner, E. M. Rodrigues and E. Hemmer, Dalton Trans., 2020, 49, 16204 DOI: 10.1039/D0DT01080D

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements