Upconversion of low‐energy photons into high‐energy photons increases the efficiency of photovoltaic devices by converting photons with energies below the absorption threshold of the solar cell into ...photons that can be utilized. In this review, an overview is provided of quantitative studies of the upconversion quantum yield of upconverter materials, and of the achieved efficiency enhancements in upconverting solar cell devices. Different materials and devices are compared based on well‐defined figures‐of‐merit and the challenges to their accurate measurement are discussed. Internal upconversion quantum yields above 13% have been reported both for Er3+‐based materials as well as for organic upconverters, using irradiance values below 0.4 W cm−2. On the upconverting solar cell device level, relative enhancements of the solar cells' short‐circuit currents by up to 0.55% have been achieved. These values document progress by orders of magnitude achieved in the last years. However, they also show that the field of upconversion needs further development to become a relevant technology option in photovoltaics. Different options regarding how upconversion performance can be increased further in the future are outlined.
Upconversion increases the efficiency of photovoltaic devices by converting photons with energies below the absorption threshold into photons that can be utilized. An overview of quantitative studies of the upconversion quantum yield of upconverter materials is provided, including the efficiency enhancements achieved for upconverter solar cell devices and different options as to how upconversion performance can be further increased.
The kinetics and thermodynamics of complex transitions in biomolecules can be modeled in terms of a network of transitions between the relevant conformational substates. Such a transition network, ...which overcomes the fundamental limitations of reaction-coordinate-based methods, can be constructed either based on the features of the energy landscape, or from molecular dynamics simulations. Energy-landscape-based networks are generated with the aid of automated path-optimization methods, and, using graph-theoretical adaptive methods, can now be constructed for large molecules such as proteins. Dynamics-based networks, also called Markov State Models, can be interpreted and adaptively improved using statistical concepts, such as the mean first passage time, reactive flux and sampling error analysis. This makes transition networks powerful tools for understanding large-scale conformational changes.
Lanthanide-doped nanocrystals are of particular interest for the research community not only due to their ability to shape light by downshifting, quantum cutting, and upconversion but also because ...novel optical properties can be found by the precise engineering of core–shell nanocrystals. Because of the large surface area-to-volume ratio of nanocrystals, the luminescence is typically suppressed by surface quenching. Here, we demonstrate a mechanism that exploits surface quenching processes to improve the luminescence of our core–shell lanthanide-doped nanocrystals. By carefully tuning the shell thickness of inert β-NaLuF4 around β-NaYF4 nanocrystals doped with Yb3+ and Er3+, we unravel the relationship between quantum yield and shell thickness, and quantify surface quenching rates for the relevant Er3+ and Yb3+ energy levels. This enhanced understanding of the system’s dynamics allowed us to design nanocrystals with a surface quenching-assisted mechanism for bright NIR to NIR downshifting with a distinctive efficiency peak for an optimized shell thickness.
We synthesized and characterized a set of ultrasmall hexagonal-phase NaGdF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles with core diameters of 3.7 ± 0.5 nm. In order to assess passivation effects ...and the influence of possible core–shell intermixing and to identify optimum particle structures for combined imaging in the visible and near-infrared (vis–NIR: 410–850 nm) and short-wave infrared (SWIR: 1520 nm), NaYF4 shells of varying thicknesses (monolayer to 10 nm) were introduced and the influence of this parameter on the upconversion and downshifting photoluminescence of these particles was studied at different excitation power densities. This included excitation power-dependent emission spectra, slope factors, quantum yields, and excited state decay kinetics. These measurements revealed enhancement factors of the upconversion quantum yield of >10 000 in the low power region and an excitation power density-independent quantum yield of the downshifted emission at 1520 nm between 0.1 and 14%. The optimized shell thickness for combined vis and SWIR imaging was identified as 5 nm. Moreover, lifetimes and quantum yields can be continuously tuned by shell thickness which can be exploited for lifetime multiplexing and encoding. The fact that we did not observe a saturation of the upconversion quantum yield or the excited state decay kinetics with increasing shell thickness is ascribed to a strong intermixing of the active core with the inert shell during the shelling procedure. This indicates the potential of spectroscopic tools to detect cation intermixing.
Myosin is a molecular motor responsible for biological motions such as muscle contraction and intracellular cargo transport, for which it hydrolyzes adenosine 5'-triphosphate (ATP). Early steps of ...the mechanism by which myosin catalyzes ATP hydrolysis have been investigated, but still missing are the structure of the final ADP·inorganic phosphate (P ᵢ) product and the complete pathway leading to it. Here, a comprehensive description of the catalytic strategy of myosin is formulated, based on combined quantum–classical molecular mechanics calculations. A full exploration of catalytic pathways was performed and a final product structure was found that is consistent with all experiments. Molecular movies of the relevant pathways show the different reorganizations of the H-bond network that lead to the final product, whose γ-phosphate is not in the previously reported HP ᵧO ₄²⁻ state, but in the H ₂P ᵧO ₄⁻ state. The simulations reveal that the catalytic strategy of myosin employs a three-pronged tactic: (i) Stabilization of the γ-phosphate of ATP in a dissociated metaphosphate (P ᵧO ₃⁻) state. (ii) Polarization of the attacking water molecule, to abstract a proton from that water. (iii) Formation of multiple proton wires in the active site, for efficient transfer of the abstracted proton to various product precursors. The specific role played in this strategy by each of the three loops enclosing ATP is identified unambiguously. It explains how the precise timing of the ATPase activation during the force generating cycle is achieved in myosin. The catalytic strategy described here for myosin is likely to be very similar in most nucleotide hydrolyzing enzymes.
Sleep is known to promote the consolidation of motor memories. In everyday life, typically more than 1 isolated motor skill is acquired at a time, and this possibly gives rise to interference during ...consolidation. Here, it is shown that reward expectancy determines the amount of sleep-dependent memory consolidation. Subjects were trained on 2 different sequences of a finger sequence motor task before 12-hr retention intervals of either nocturnal sleep or daytime wakefulness. After training was finished, reward expectancy was varied by announcing a monetary reward for performance improvement at retesting on either the first- or second-trained sequence. Before the retest, however, subjects were informed that reward would depend not on only 1 sequence but on the average performance for both sequences. Posttraining sleep enhanced overall finger sequence performance. The sleep-dependent gain in skill was significantly greater for the sequence that was associated with monetary reward after training, regardless of whether this sequence was the first or second to be trained. After wake retention intervals, no or only minor performance gains were observed. The data show that expectancy for a reward enhances offline learning of a skill during sleep.
Organometal halide perovskites have recently emerged displaying a huge potential for not only photovoltaic, but also light emitting applications. Exploiting the optical properties of specifically ...tailored perovskite nanocrystals could greatly enhance the efficiency and functionality of applications based on this material. In this study, we investigate the quantum size effect in colloidal organometal halide perovskite nanoplatelets. By tuning the ratio of the organic cations used, we can control the thickness and consequently the photoluminescence emission of the platelets. Quantum mechanical calculations match well with the experimental values. We find that not only do the properties of the perovskite, but also those of the organic ligands play an important role. Stacking of nanoplatelets leads to the formation of minibands, further shifting the bandgap energies. In addition, we find a large exciton binding energy of up to several hundreds of meV for nanoplatelets thinner than three unit cells, partially counteracting the blueshift induced by quantum confinement. Understanding of the quantum size effects in perovskite nanoplatelets and the ability to tune them provide an additional method with which to manipulate the optical properties of organometal halide perovskites.
3D DNA Origami Crystals Zhang, Tao; Hartl, Caroline; Frank, Kilian ...
Advanced materials (Weinheim)
30, Številka:
28
Journal Article
Recenzirano
Odprti dostop
3D crystals assembled entirely from DNA provide a route to design materials on a molecular level and to arrange guest particles in predefined lattices. This requires design schemes that provide high ...rigidity and sufficiently large open guest space. A DNA‐origami‐based “tensegrity triangle” structure that assembles into a 3D rhombohedral crystalline lattice with an open structure in which 90% of the volume is empty space is presented here. Site‐specific placement of gold nanoparticles within the lattice demonstrates that these crystals are spacious enough to efficiently host 20 nm particles in a cavity size of 1.83 × 105 nm3, which would also suffice to accommodate ribosome‐sized macromolecules. The accurate assembly of the DNA origami lattice itself, as well as the precise incorporation of gold particles, is validated by electron microscopy and small‐angle X‐ray scattering experiments. The results show that it is possible to create DNA building blocks that assemble into lattices with customized geometry. Site‐specific hosting of nano objects in the optically transparent DNA lattice sets the stage for metamaterial and structural biology applications.
A DNA‐origami‐based triangle structure assembles into a 3D rhombohedral crystalline lattice. The accurate assembly of the DNA origami lattice itself as well as the precise incorporation of gold particles is demonstrated by electron microscopy and small‐angle X‐ray scattering experiments.
Mental mapping is a method of interpreting with conceptual metaphors. This method is applied to the admiration song in Song of Songs 7:2–7. The song is interpreted in the context of a dance. For the ...purpose of interpretation, ancient Egyptian dance paintings and love poems are taken into account. The interpretation presents a methodological study that unmasks arbitrary exegesis and implausible interpretations. It discovers its subtle conceptual metaphors and shows a strategy for a comprehensible exegesis. As a side effect, the male chauvinism present in this song is deconstructed
In cooperative breeding systems, dominant breeders sometimes tolerate unrelated individuals even if they inflict costs on the dominants. According to the ‘pay-to-stay’ hypothesis, (i) subordinates ...can outweigh these costs by providing help and (ii) dominants should be able to enforce help by punishing subordinates that provide insufficient help. This requires that dominants can monitor helping and can recognize group members individually. In a field experiment, we tested whether cooperatively breeding cichlid Neolamprologus pulcher subordinates increase their help after a forced ‘idle’ period, how other group members respond to a previously idle helper, and how helper behaviour and group responses depend on group size. Previously, idle helpers increased their submissiveness and received more aggression than control helpers, suggesting that punishment occurred to enforce help. Subordinates in small groups increased their help more than those in large groups, despite receiving less aggression. When subordinates were temporarily removed, dominants in small groups were more likely to evict returning subordinates. Our results suggest that only in small groups do helpers face a latent threat of punishment by breeders as predicted by the pay-to-stay hypothesis. In large groups, cognitive constraints may prevent breeders from tracking the behaviour of a large number of helpers.
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