| 1. |
- Alvarez, Sol Laura Gutierrez, et al.
(författare)
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Morphology-Dependent One- and Two-Photon Absorption Properties in Blue Emitting CsPbBr3Nanocrystals
- 2022
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:22, s. 4897-4904
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Tidskriftsartikel (refereegranskat)abstract
- The linear and nonlinear optical parameters and morphologic dependence of CsPbBr3 nanocrystals (NCs) are crucial for device engineering. In particular, such information in asymmetric nanocrystals is still insufficient. We characterized the OPLA (σ1) and TPA cross sections (σ2) of a series CsPbBr3 nanocrystals with various aspect ratios (AR) using femtosecond transient absorption spectroscopy (TAS). The σ1 presents a linear volume dependence of all the samples, which agrees with the previous behavior in CsPbBr3 QDs. However, the σ2 values do not exhibit conventional power dependency of the crystal volume but are also modulated by the shape-dependent local field factors. In addition, the local field effect in CsPbBr3 NCs is contributed by their asymmetric morphologies and polar ionic lattices, which is more pronounced than in conventional semiconductor NCs. Finally, we revealed that the lifetimes of photogenerated multiexcitonic species of those nanocrystals feature identical morphology independence in both OPLA and TPA.
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| 2. |
- Bamini, Sesha, et al.
(författare)
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Time-resolved terahertz spectroscopy reveals the influence of charged sensitizing quantum dots on the electron dynamics in ZnO
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:8, s. 6006-6012
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Tidskriftsartikel (refereegranskat)abstract
- Photoinitiated charge carrier dynamics in ZnO nanoparticles sensitized by CdSe quantum dots is studied using transient absorption spectroscopy and time-resolved terahertz spectroscopy. The evolution of the transient spectra shows that electron injection occurs in a two-step process, where the formation of a charge transfer state (occurring in several picoseconds) is followed by its dissociation within tens of picoseconds. The photoconductivity of electrons injected into the ZnO nanoparticles is lower than that of charges photogenerated directly in ZnO. We conclude that the motion of injected electrons in ZnO nanoparticles is strongly influenced by their interaction with positive charges left in the sensitizing quantum dots.
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| 3. |
- Beenken, Wichard, et al.
(författare)
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Excitonic coupling in polythiophenes: Comparison of different calculation methods
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:5, s. 2490-2495
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Tidskriftsartikel (refereegranskat)abstract
- In conjugated polymers the optical excitation energy transfer is usually described as Forster-type hopping between so-called spectroscopic units. In the simplest approach using the point-dipole approximation the transfer rate is calculated based on the interaction between the transition dipoles of two spectroscopic units. In the present work we compare this approach with three others: The line-dipole approximation, the Coulomb integral between the transition densities, and a quantum-chemical calculation of the interacting dimer as entity. The latter two approaches are based on the semiempirical method ZINDO. The line-dipole approximation is an attractive compromise between computational effort and precision for calculations of the excitonic coupling in extended conjugated polymers. (C) 2004 American Institute of Physics.
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| 4. |
- Beenken, W J D, et al.
(författare)
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Excited state properties of neutral and charged ter-fluorene with and without a keto-defect
- 2008
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Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 245:5, s. 849-853
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Tidskriftsartikel (refereegranskat)abstract
- Stimulated by the recent experimental report of optical properties of charged oligofluorenes [S. Fratiloiu et al., J. Phys. Chem. B 210, 59845993 (2006)], we have used time-dependent density functional theory (TD-DFT) to study the electronic structure of neutral and charged ter-fluorene with and without keto-defect. We have characterized the excited states by site- and space-based representations of the density matrix. For the defectless neutral species we found typical excitons, while the first excited states of the corresponding charged species represent long-range oscillations of the electron or hole along the whole oligomer. For the neutral ketonized ter-fluorene we found trapping of the excited electron. Similarly, the unpaired electron of the anion ground' state is trapped. The excited state properties of the cation; however, are insensitive to the keto-defect.
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| 5. |
- Beenken, Wichard, et al.
(författare)
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Potential surfaces and delocalization of excitons in dimers
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:12, s. 5810-5820
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we will demonstrate that the nuclear dynamics have a strong influence on the delocalization of an exciton in a dimer, even if they do not effect the excitonic interaction. It will be shown that the internal nuclear conformation of the molecules forming the dimer depends critically on the delocalization of the exciton state in the dimer and vice versa. The resulting closed loop enforces a localization of the lower excitonic state, but, contrary to the commonly accepted view, a delocalization of the upper one. Qualitatively different time-evolution of the delocalization length for the lower and upper excitonic state will be shown. Besides, it will turn out that the nuclear motions inhibit a complete delocalization of the excitonic state in any case. To accomplish nuclear and exciton dynamics, the nonadiabatic coupling between the two excitonic states will be deduced. This causes a relaxation from the upper to the lower excitonic state, which limits the maximum reachable exciton delocalization.
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| 6. |
- Beenken, Wichard, et al.
(författare)
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Spectroscopic units in conjugated polymers: A quantum chemically founded concept?
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:20, s. 6164-6169
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Tidskriftsartikel (refereegranskat)abstract
- In conjugated polymers the concept of spectroscopic units belonging to different spatial segments of the chain, which are responsible for the spectroscopic properties of the polymer, has been used to explain the spectral heterogeneity and the excitation migration by (Forster type) hopping transfer. In the present work we study the possible mechanism of segmentation of polythiophene into spectroscopic units by using quantum-chemical methods (ZINDO). We found that static geometric defects such as kinks or torsions do not result in a significant localization of the excited states to a certain segment. Hence, we propose that a dynamic localization of excitation due to the interaction between the nuclear and electronic degrees of freedom is responsible for the formation of the spectroscopic units.
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| 7. |
- Benazzi, Elisabetta, et al.
(författare)
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Acid-triggering of light-induced charge-separation in hybrid organic/inorganic molecular photoactive dyads for harnessing solar energy
- 2021
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Ingår i: Inorganic Chemistry Frontiers. - : Royal Society of Chemistry (RSC). - 2052-1553. ; 8:6, s. 1610-1618
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Tidskriftsartikel (refereegranskat)abstract
- H+ modulated charge-transfer in photoexcited covalent polyoxometalate-bodipy conjugates is described. The hybrid organic/inorganic molecular photoactive dyads are based on Keggin-type polyoxometalates (POMs, where KM = [PM11O39] and M = Mo or W) covalently grafted via an organotin linker to a bodipy (BOD) photosensitizer. The relative potentials of the photosensitizer and POM are aligned such that light-induced electron transfer from BOD to POM is permitted for the polyoxomolybdate KMoSn[BOD] but not effective for the polyoxotungstate analogue KWSn[BOD]. In both cases, the addition of acid shifts the redox potential of the POM only, to increase the driving force for electron transfer. This leads to charge-separation being switched on for KWSn[BOD] in the presence of acid. The addition of acid to KMoSn[BOD] accelerates charge-separation by an order of magnitude (from 2 ns to 200 ps) and is accompanied by a deceleration of charge recombination, leading to a charge-separated state lifetime of up to 1.3 μs. This behaviour is consistent with proton coupled electron transfer, which has previously been observed electrochemically for POMs, but this study shows, for the first time, the impact of protonation on photoinduced electron transfer. This journal is
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| 8. |
- Bi, Chenghao, et al.
(författare)
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Spontaneous Self-Assembly of Cesium Lead Halide Perovskite Nanoplatelets into Cuboid Crystals with High Intensity Blue Emission
- 2019
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Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 6:13
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal all-inorganic perovskite nanocrystals have gained significant attention as a promising material for both fundamental and applied research due to their excellent emission properties. However, reported photoluminescence quantum yields (PL QYs) of blue-emitting perovskite nanocrystals are rather low, mostly due to the fact that the high energy excitons for such wide bandgap materials are easily captured by interband traps, and then decay nonradiatively. In this work, it is demonstrated how to tackle this issue, performing self-assembly of 2D perovskite nanoplatelets into larger size (≈50 nm × 50 nm × 20 nm) cuboid crystals. In these structures, 2D nanoplatelets being isolated from each other within the cuboidal scaffold by organic ligands constitute multiple quantum wells, where exciton localization on potential disorder sites helps them to bypass nonradiative channels present in other platelets. As a result, the cuboid crystals show an extremely high PL QY of 91% of the emission band centered at 480 nm. Moreover, using the same synthetic method, mixed-anion CsPb(Br/Cl) 3 cuboid crystals with blue emission peaks ranging from 452 to 470 nm, and still high PL QYs in the range of 72–83% are produced.
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| 9. |
- Bi, Chenghao, et al.
(författare)
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Stable CsPb1- xZn xI3Colloidal Quantum Dots with Ultralow Density of Trap States for High-Performance Solar Cells
- 2020
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 32:14, s. 6105-6113
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Tidskriftsartikel (refereegranskat)abstract
- All inorganic halide perovskites in the form of colloidal quantum dots (QDs) have come into people's view as one of the potential materials for the high-efficiency solar cells; nevertheless, the high surface trap density and poor stability of QDs restrict the performance improvement and application. Here, we obtain colloidal inorganic perovskite CsPb1-xZnxI3 QDs by the hot-injection synthesis process with the addition of ZnCl2. Synchrotron-based X-ray absorption fine structures demonstrate that the guest Zn2+ ions are doped into the CsPbI3 structure to improve the local ordering of the lattice of the perovskite, reducing the octahedral distortions. The increase of the Goldschmidt tolerance factor and the Pb-I bond energy also enhance the stability of the perovskite structure. Furthermore, the Cl- ions from ZnCl2 occupy the iodide vacancies of the perovskite to decrease the nonradiative recombination. The synergistic effect of doping and defect passivation makes for stable colloidal CsPb0.97Zn0.03I3 QDs with ultralow density of trap states. The champion solar cell based on the QDs shows a power conversion efficiency of 14.8% and a largely improved stability under ambient conditions.
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| 10. |
- Brueggemann, Ben, et al.
(författare)
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Nonperturbative modeling of fifth-order coherent multidimensional spectroscopy in light harvesting antennas
- 2011
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in coherent multidimensional spectroscopy have boosted interest in exciton coherences in light harvesting complexes. We present nonperturbative calculations of two-dimensional (2D) electronic spectroscopy from a fifth-order phase-matching direction. The calculations show clear patterns that correspond to the electronic structure of one- and two-exciton manifolds of a Fenna-Matthews-Olsson light harvesting complex. Such signals can provide new information about the coherent properties of antenna pigment protein complexes.
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