Influence of Lu<sup>3+</sup> Doping on the Crystal Structure of Uniform Small (5 and 13 nm) NaLnF<sub>4</sub> Upconverting Nanocrystals
Bibliographic record
Abstract
While there have been many advances in techniques to synthesize uniform lanthanide-doped upconversion nanoparticles (UCNPs), it is still a challenge to synthesize small (ca. 5 nm) hexagonal phase UCNPs that are also bright. The most common method to obtain strongly emissive UCNPs is to synthesize core–shell structures with a passivating shell coating the luminescent core. This approach normally results in larger NPs (>20 nm) and requires two-step procedures. Here, we report a one-pot synthesis of 4 nm NaLuF 4:Gd(37%),Yb(16%),Er(2%) UCNPs, whose colloidal solutions show upconversion luminescence (UCL) visible to the eye. We initially hypothesized that the origin of UCL from such small UCNPs was due to a Gd-rich hexagonal upconverting core containing Yb and Er with a Lu-rich passivating shell. This idea is based on the different nucleation rates of the NaLnF 4 NPs. Interestingly, the 4 nm NaLuF 4 -based UCNPs are in the cubic phase, and subsequently undergo a phase transformation with prolonged heating to form larger (12–14 nm) uniform hexagonal phase UCNPs. We also found that if the molar ratio of Lu:Gd in the reaction mixture was decreased from 45:37 to 20:62, the resulting UCNPs still initially nucleated in the cubic phase. Additional studies in which we varied other reaction parameters (temperature, ratios of Na + /Ln 3+ and F – /Ln 3+, and solvent composition) also resulted in initial nucleation in the cubic phase. In contrast, both the NaGdF 4:Yb,Er and NaYF 4:Gd,Yb,Er UCNPs nucleated in the hexagonal phase. Our results suggest that the presence of Lu in the reaction mixture influences the nucleation of NaLnF 4 NPs. Lanthanide compositions that would normally nucleate in the hexagonal phase appear to nucleate in the cubic phase when Lu is present.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".