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- Yang, Wenxing, et al.
(författare)
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Surface passivation extends single and biexciton lifetimes of InP quantum dots
- 2020
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Ingår i: Chemical Science. - : ROYAL SOC CHEMISTRY. - 2041-6520 .- 2041-6539. ; 11:22, s. 5779-5789
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Tidskriftsartikel (refereegranskat)abstract
- Indium phosphide quantum dots (InP QDs) are nontoxic nanomaterials with potential applications in photocatalytic and optoelectronic fields. Post-synthetic treatments of InP QDs are known to be essential for improving their photoluminescence quantum efficiencies (PLQEs) and device performances, but the mechanisms remain poorly understood. Herein, by applying ultrafast transient absorption and photoluminescence spectroscopies, we systematically investigate the dynamics of photogenerated carriers in InP QDs and how they are affected by two common passivation methods: HF treatment and the growth of a heterostructure shell (ZnS in this study). The HF treatment is found to improve the PLQE up to 16-20% by removing an intrinsic fast hole trapping channel (tau(h,non)= 3.4 +/- 1 ns) in the untreated InP QDs while having little effect on the band-edge electron decay dynamics (tau(e)= 26-32 ns). The growth of the ZnS shell, on the other hand, is shown to improve the PLQE up to 35-40% by passivating both electron and hole traps in InP QDs, resulting in both a long-lived band-edge electron (tau(e)> 120 ns) and slower hole trapping lifetime (tau(h,non)> 45 ns). Furthermore, both the untreated and the HF-treated InP QDs have short biexciton lifetimes (tau(xx)similar to 1.2 +/- 0.2 ps). The growth of an ultra-thin ZnS shell (similar to 0.2 nm), on the other hand, can significantly extend the biexciton lifetime of InP QDs to 20 +/- 2 ps, making it a passivation scheme that can improve both the single and multiple exciton lifetimes. Based on these results, we discuss the possible trap-assisted Auger processes in InP QDs, highlighting the particular importance of trap passivation for reducing the Auger recombination loss in InP QDs.
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| 3. |
- Yang, Wenxing, et al.
(författare)
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Photoinduced Fano Resonances between Quantum Confined Nanocrystals and Adsorbed Molecular Catalysts
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:13, s. 5813-5818
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Tidskriftsartikel (refereegranskat)abstract
- Interaction of surface adsorbate vibration and intraband electron absorption in nanocrystals has been reported to affect the photophysical properties of both nanocrystals and surface adsorbates and may affect the performance of hybrid photocatalysts composed of semiconductor nanocrystals and molecular catalysts. Here, by combining ultrafast transient visible and IR spectroscopic measurements, we report the observation of Fano resonances between the intraband transition of the photogenerated electrons in CdS and CdSe nanocrystals and CO stretching vibrational modes of adsorbed molecular catalysts, [Fe-2(cbdt)(CO)(6)] (FeFe; cbdt = 1-carboxyl-benzene-2,3-dithiolate), a molecular mimic for the active site of FeFe-hydrogenase. The occurrence of Fano resonances is independent of nanocrystal types (rods vs dots) or charge transfer character between the nanocrystal and FeFe, and is likely a general feature of nanocrystal and molecular catalyst hybrid systems. These results provide new insights into the fundamental interactions in these hybrid assemblies for artificial photosynthesis.
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- Zheng, Shao Fei, et al.
(författare)
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An inverse optimization of turbulent flow and heat transfer for a cooling passage with hierarchically arranged ribs in turbine blades
- 2024
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 220
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Tidskriftsartikel (refereegranskat)abstract
- Owing to the limited cold-air amount and pressure in supply systems, high-efficient heat transfer with low-level friction loss is highly desired for cooling units of a turbine blade. To exploit the potential improvement of hierarchically arranged ribs in cooling passages proposed previously, multi-parameter optimizations for rib arrangements are implemented by integrating the simplified conjugate-gradient algorithm with the turbulent flow and heat transfer model. Rib heights as design variables are optimized with various performance indices as objective functions at a fixed Re. The optimizations confirm that using the wall temperature difference and Nu as the objective function, respectively, a limited heat transfer improvement is achieved with a greatly increased friction loss. Taking the overall performance factor as the objective function, different optimal designs at different constraint conditions possess hierarchical characteristics. A significant friction loss reduction of 52.1%, 54.7%, and 54.8%, is achieved with a moderate heat transfer loss of 10.9%, 7.0%, and 2.3%. Despite different thermal and friction performances, their overall performances are consistent with a remarkable increase of 13.9%, 21.2%, and 27.3%. Finally, the optimization strategy coupling the multi-parameter optimization and hierarchical scheme is confirmed as effective for enhancing the thermohydraulic performance of convective heat transfer systems with perturbation elements.
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