Controlling the Luminescence of Rare-Earth Chalcogenide Iodides <i>RE</i><sub>3</sub>(Ge<sub>1–<i>x</i></sub>Si<sub><i>x</i></sub>)<sub>2</sub>S<sub>8</sub>I (<i>RE</i> = La, Ce, and Pr) and Ce<sub>3</sub>Si<sub>2</sub>(S<sub>1–<i>y</i></sub>Se<sub><i>y</i></sub>)<sub>8</sub>I
Bibliographic record
Abstract
The rare-earth chalcogenide iodides RE 3 (Ge 1– x Si x ) 2 S 8 I ( RE = La, Ce, and Pr) and Ce 3 Si 2 (S 1– y Se y ) 8 I were prepared by reactions of the elements at 900 °C. Phase-pure samples and complete solid solutions were obtained for all series, as determined by powder X-ray diffraction patterns, with the cell parameters evolving smoothly. They adopt the monoclinic La 3 Si 2 O 8 Cl-type structure (space group C 2/ c ), containing isolated tetrahedra centered by the tetrel atoms and separated by the RE and I atoms. Single-crystal X-ray diffraction studies indicate that substitution of Si for Ge atoms in RE 3 (Ge 1– x Si x ) 2 S 8 I leads to complete disorder of the tetrel atoms, whereas partial substitution of Se for S atoms in Ce 3 Si 2 (S 1– y Se y ) 8 I occurs with preferential occupation of Se atoms. The optical band gaps increase slightly upon substitution with Si in RE 3 (Ge 1– x Si x ) 2 S 8 I (or negligibly in the case of the Ce-containing series, remaining at 2.8 eV), and they decrease dramatically upon substitution with Se in Ce 3 Si 2 (S 1– y Se y ) 8 I, from 2.8 to 1.9 eV. These band gaps are direct according to electronic structure calculations. The strong blue photoluminescence emission in Ce 3 Si 2 S 8 I shifts slightly to blue-green in Ce 3 (Ge 0.25 Si 0.75 ) 2 S 8 I and significantly to green in Ce 3 Si 2 (S 0.81 Se 0.19 ) 8 I, as quantified by their chromaticity coordinates. Increasing the concentration of Ge or Se tends to decrease the photoluminescence intensity and lifetime. For Ce 3 Si 2 S 8 I, the activation energy for thermal quenching is 0.68 eV.
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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".