Exciton Recombination and Upconverted Photoluminescence in Colloidal CdSe Quantum Dots
Bibliographic record
Abstract
We studied photoluminescence (PL) of colloidal CdSe quantum dots (QDs) synthesized by a single-step method using cadmium oxide (CdO) and tri- n -octylphosphine selenide (TOPSe) as the Cd and Se sources, respectively, and tri- n -octylphosphine (TOP) as the reaction medium and subsequently dispersed in hexane. The QDs were excited by a narrow-band incoherent cw light source with photon energies near or below the first absorption maximum of the sample, and the resulting luminescence was dispersed and recorded. In the PL spectra, we identified two displaced by ∼16−38 meV strongly overlapping components with excitation energy dependent intensities. We also investigated lifetimes of the nonresonant PL decay at various excitation and emission energies using a frequency-domain method and observed multiexponential decay with three lifetimes approximately equal to 11.5(1.0), 41(2), and 155(15) ns. The low-energy component with the full width at half-maximum (fwhm) ranging from 135−155 meV was assigned to the charged exciton emission correlating with the shortest lifetime. The narrower high-energy component with the fwhm ranging from 80−90 meV was attributed to the band edge exciton emission with the middle lifetime. Photoexcitation of the QD sample in the onset of the absorption tail yielded blue-shifted (upconverted) luminescence. The blue-shifted PL was determined to result from a single-photon excitation. Therefore, we claimed that the upconversion process was thermally assisted. Numerical modeling showed the blue shift to be consistent with room temperature thermal phonon distribution in the colloidal QDs.
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How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".