Local Structure of Rare-Earth Fluorides in Bulk and Core/Shell Nanocrystalline Materials
Bibliographic record
Abstract
NaREF 4 (rare-earth, RE = Y, Lu) nanocrystals (NCs) containing Ln 3+ -dopants are of great interest due to their unique ability to downshift, downconvert, and upconvert light. While the luminescent properties and microscale structures of such NCs are well understood, relatively little is known about their molecular-level structures, the nature of the NC cores and shells, and the interactions of the stabilizing ligands at the NC surface. To address these issues, we present a comprehensive characterization of bulk β-NaYF 4, one of the most commonly used hosts for Ln 3+ -dopants in luminescent NCs. Using a combination of powder X-ray diffraction (pXRD) and multinuclear ( 89 Y, 23 Na, 19 F) solid-state nuclear magnetic resonance (SSNMR) spectroscopy, we provide conclusive evidence that this compound crystallizes in a hexagonal P 6 3 / m structure, resolving a longstanding debate. The structure of this bulk form is related to the structure of NaYF 4 /NaLuF 4 core/shell NCs. From the similarities between the 19 F and 23 Na SSNMR spectra of the bulk and NC materials, it is concluded that the NCs have the same β-NaYF 4 and β-NaLuF 4 phases as the bulk compounds. A series of cross-polarization NMR experiments confirm the presence of oleates on the surface of the particle via their proximity to surface Na + sites.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".