Laser coupling in indirect bandgap Ge nanocrystals
Bibliographic record
Abstract
In this study, we present the first observation of laser cooling in an indirect bandgap semiconductor. Utilizing precise Raman measurements, we detected dominant anti-Stokes photoluminescence in germanium nanocrystals with average particle sizes ranging from 16 nm to 30 nm. These measurements were consistently reproducible in two distinct experimental setups: germanium nanocrystals in isopropyl alcohol (IPA) solution and dispersed germanium nanocrystal powder. From these observations, we inferred lattice temperatures as low as approximately 50K. This cooling effect can be attributed to several converging factors: ultra-high purity of the germanium nanocrystals, generation of a high-density electron-hole plasma, inherent degeneracy of longitudinal and transverse optical phonons in non-polar indirect bandgap semiconductors, and corresponding confinement effects. Our findings underscore the critical role of laser power density in solid-state cooling, identifying a threshold level that induces dominant anti-Stokes emission.
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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) | 0.002 | 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".