Non-Injection and Low-Temperature Approach to Colloidal Photoluminescent PbS Nanocrystals with Narrow Bandwidth
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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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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 | 0.000 | 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) | 0.000 | 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 it