Non-Injection and Low-Temperature Approach to Colloidal Photoluminescent PbS Nanocrystals with Narrow Bandwidth
Bibliographic record
Abstract
Colloidal photoluminescent (PL) PbS nanocrystals have attracted a lot of attention in various applications such as bioimaging and optical telecommunications due to their tunable bandgap in the near-infrared region of the electromagnetic spectrum. Hot-injection processes seem to be the best to engineer high-quality PbS nanocrystals. However, there is a limited body of literature documented on the syntheses, with little information on synthetic parameters affecting the optical properties of the product. Moreover, small PbS nanocrystals with large bandgap greater than 1.38 eV (ca. 900 nm) and narrow bandwidth are rarely reported, due to the fact that high-temperature growth in hot-injection processes leads to large nanocrystals rapidly. This manuscript deals with our noninjection and low temperature approach to small PbS nanocrystal ensembles with bandgap in wavelength shorter than 900 nm and with narrow bandwidth; the growth temperature can be as low as room temperature. For our noninjection approach, systematic study was performed on synthetic parameters affecting the growth, with the growth temperature in the range of 30−120 °C and octadecene (ODE) as a reaction medium. Different acids including oleic aicd (OA) were explored as surface ligands, while two lead source compounds, which are lead oxide (PbO) and lead acetate, and three S source compounds, which are bis(trimethylsilyl)sulfide ((TMS) 2 S), thioacetamide (TAA), and elemental sulfur (S), were investigated. Generally, a solution of a lead precursor in ODE was first prepared via a reaction of a Pb-source compound and an acid; afterward, this solution was mixed with a S-source solution in ODE at room temperature. The use of (TMS) 2 S and OA bestows high-quality PbS nanocrystals, regarding narrow bandwidth of bandgap absorption and photoemission, without storage in dark for digestive and Ostwald ripening leading to self-focusing; in addition to the various acids and Pb and S source compounds explored, feed molar ratios of acid-to-Pb and Pb-to-S, as well as reactant concentrations were thoroughly investigated. Low acid-to-Pb and high Pb-to-S feed molar ratios together with high-reactant concentrations favor the formation of small PbS nanocrystals; meanwhile, from one synthetic batch, the growth of PbS nanocrystals in size is tunable mainly via temperature in addition to growth periods. The PbS nanocrystals exhibit bandwidth (full width at half-maximum) as narrow as ca. 100 nm with growth temperature of 70 °C. Thus, our noninjection approach features easy handling with high reproducibility and high-quality PbS nanocrystals with large bandgap but narrow bandwidth. Finally, bandgap engineering of our as-synthesized PbS nanocrystals was performed straightforwardly at room temperature via the mixing of a solution of Cd oleate in ODE; significant blueshift of bandgap absorption and photoemission with enhanced PL efficiency was accomplished.
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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".