Photoluminescent Colloidal CdS Nanocrystals with High Quality via Noninjection One-Pot Synthesis in 1-Octadecene
Bibliographic record
Abstract
High-quality colloidal photoluminescent CdS quantum dots (QDs) were synthesized via a noninjection one-pot approach in noncoordinating solvent 1-octadecene. This synthetic approach uses cadmium acetate dihydrate and elemental sulfur as Cd and S sources, respectively, together with one long-chain fatty acid (CH 3 −(CH 2 ) n −COOH) as surface ligands and 2,2′-dithiobisbenzothiazole (MBTS) to increase sulfur activity. The CdS QDs were synthesized at elevated temperatures such as 240−300 °C, and the kinetics of nucleation/growth was monitored via the temporal evolution of the optical properties of the growing CdS QDs. Various synthetic parameters were investigated, such as the feed molar ratios of (0.5−8)Cd/1S and (2−64)S/1MBTS, reactant concentrations of 5−80 mmol/Kg, and growth temperature of 220−350 °C. The feed molar ratios of (1−2)Cd/1S and (8−32)S/1MBTS are suggested to be the optimal synthetic window, together with the S feed concentration of 10−20 mmol/Kg and the growth temperature of 240−260 °C. Moreover, ligand effects such as ligand length and concentration were thoroughly investigated. With an increase of the chain length of the fatty acid, the size of the resulting CdS QDs was systematically reduced. The acids of moderate carbon-chain length ( n = 10−16) bestowed CdS QDs in high quality regarding narrow size distribution (∼17−22 nm in full width at half-maximum), high nanocrystal yield, and high quantum yield (up to 30%). Meanwhile, the acids with longer carbon chain led to small-sized nanocrystals in low concentration, due to large steric hindrance retarding severely the nucleation and growth, as indicated by the late appearance of nanocrystal absorption and slow increase in size. The acids with shorter carbon chain resulted in large-sized nanocrystals in low concentration, due to small steric hindrance causing ready nucleation and growth, as indicated by the large and fast increase in size. Therefore, the steric hindrance of varied-length fatty acids affects the reactivity of Cd 2+ with great impacts on the nanocrystal nucleation/growth and thus the nanocrystal size and surface passivation. Furthermore, with an increase in the acid concentration, the size and size distribution of the resulting CdS QDs increased, together with a decrease in nanocrystal yield, due to an enhanced solubility of the CdS nanocrystals and thus a hindered nucleation with a low nuclei concentration.
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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".