Projects per year
Abstract
Fluorite is one of the most common minerals in the crust and is of
widespread economic importance. It shows strong UV-excited luminescence,
variously attributed to defects within the fluorite structure and
lanthanide substitutions. We present here a detailed chemical
characterisation of a suite of natural fluorite samples, chosen to
represent the range of compositions observed in nature. We perform X-ray
excited luminescence spectroscopy on the samples as a function of
temperature (20–673 K) in the wavelength range 250–800 nm to provide
insights into physical defects in the lattice and their interactions
with lanthanide substituents in natural fluorite. Most broad bands in
the UV are attributed to electronic defects in the fluorite lattice,
whereas sharp emissions are attributed to intra-ion energy cascades in
trivalent lanthanides. Lanthanides are accommodated in fluorite by
substitution for Ca2+ coupled with interstitial F−, O2− (substituting for F−)
and a variety of electronic defect structures which provide local
charge balance. The chondrite-normalised lanthanide profiles show that
fluorite accommodates a greater proportion of heavy lanthanides (and Y)
as the total Rare Earth Element (REE) concentration increases; whereas
cell parameters decrease and then increase as substitution continues.
Luminescence intensity also goes through a maximum and then decreases as
a function of REE concentration. All three datasets are consistent with
a model whereby lanthanides initially act as isolated centres, but,
beyond a critical threshold (~ 1000 ppm), cluster into lanthanide-rich
domains. Clustering results in shorter REE-O bond distances (favouring
smaller heavier ions), a larger unit cell but more efficient energy
transfer between lanthanides, thereby promoting non-radiative energy
loss and a drop in the intensity of lanthanide emission.
Original language | English |
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Article number | 15 |
Number of pages | 14 |
Journal | Physics and Chemistry of Minerals |
Volume | 50 |
DOIs | |
Publication status | Published - 27 Apr 2023 |
Keywords
- XEOL
- Radioluminescence
- Defect clustering
- Lanthanides
- Rare earths
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Dive into the research topics of 'Lanthanide and yttrium substitution in natural fluorite'. Together they form a unique fingerprint.Projects
- 2 Finished
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Security of Supply of Rare Earth Element: SoS RARE - Security of Supply of Rare Earth Elements
Finch, A. A. (PI)
1/05/15 → 31/12/19
Project: Standard
Datasets
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Lanthanide and yttrium substitution in natural fluorite (dataset)
Finch, A. A. (Creator), Horsburgh, N. (Creator) & Friis, H. (Creator), University of St Andrews, 28 Apr 2025
DOI: 10.17630/1f1d9f50-ded0-4944-811d-496dfdbef38f
Dataset