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The Catalytic Cycle of Water Oxidation in Crystallized Photosystem II Complexes: Performance and Requirements for Formation of Intermediates
摘要： Crystals of Photosystem II (PSII) contain the most homogeneous copies of the water-oxidizing reaction center where O2 is evolved (WOC). However, few functional studies of PSII operation in crystals have been carried out, despite their widespread use in structural studies. Here we apply oximetric methods to determine the quantum efficiency and lifetimes of intermediates of the WOC cycle as a function of added electron acceptors (quinones and ferricyanide), both aerobically and anaerobically. PSII crystals exhibit the highest quantum yield of O2 production yet observed of any native or isolated PSII (61.6%, theoretically 59,000 μmol O2/mg Chl/h). WOC cycling can be sustained for thousands of turnovers using an irreversible electron acceptor (ferricyanide). Simulations of the catalytic cycle identify four distinct photochemical inefficiencies in both PSII crystals and dissolved PSII cores that are nearly the same. The exogenous acceptors equilibrate with the native plastoquinone acceptor at the QB (or QC) site(s), for which two distinct redox couples are observable that regulate flux through PSII. Flux through the catalytic cycle of water oxidation is shown to be kinetically restricted by the QAQB two-electron gate. The lifetimes of the S2 and S3 states are greatly extended (especially S2) by electron acceptors and depend on their redox reversibility. PSII performance can be pushed in vitro far beyond what it is capable of in vivo. With careful use of precautions and monitoring of populations, PSII microcrystals enable the exploration of WOC intermediates and the mechanism of catalysis.
关键词： oxygen-evolving complex,electron acceptors,(micro)crystals,S states,quantum yield,Photosystem II
更新于2025-09-23 15:22:29
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Photocatalytic Hydrogen Production Under Near-UV Using Pd-Doped Mesoporous TiO2 and Ethanol as Organic Scavenger
摘要： Photocatalysis can be used advantageously for hydrogen production using a light source (near-UV light), a noble metal-doped semiconductor and an organic scavenger (2.0 v/v% ethanol). With this end, palladium was doped on TiO2 photocatalysts at different metal loadings (0.25 to 5.00 wt%). Photocatalysts were synthetized using a sol-gel method enhancing morphological properties with a soft template precursor. Experiments were carried out in the Photo-CREC Water II reactor system developed at CREC-UWO (Chemical Reactor Engineering Centre- The University of Western Ontario) Canada. This novel unit offers hydrogen storage and symmetrical irradiation allowing precise irradiation measurements for macroscopic energy balances. Hydrogen production rates followed in all cases a zero-order reaction, with quantum yields as high as 30.8%.
关键词： Quantum Yield,Photo-CREC Water II reactor,Palladium,Hydrogen production,TiO2
更新于2025-09-23 15:22:29
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A DNA-Encapsulated Silver Cluster and the Roles of Its Nucleobase Ligands
摘要： Silver clusters consisting of ~10 atoms are readily bound by and encapsulated within DNA strands to yield strong absorption and emission. The coordination environments, however, are poorly understood, so cluster adducts can only be empirically tuned. This work describes the C4AC4TC3G strand that templates a particular cluster adduct. Its sequence has three types of nucleobases with distinct roles – tracts of cytosines that collectively coordinate the cluster, thymine acting as a junction in the overall strand, and the adenine/guanine pair that exclusively forms the cluster. In relation to the native oligonucleotide, the DNA-silver cluster complex diffuses faster and is more compact, thus suggesting that the strands folds because of the cluster. The Ag10 6+ adduct emits with λex/λem = 490/540 nm, a 19% quantum yield, and a biexponential 1.1/2.1 ns lifetime. The electronic environment for the cluster is controlled by the heteroatoms in the adenine and guanine. Most significantly, the N7 and the N2 in the guanine change the fluorescence quantum yield by 60-fold and shift the fluorescence lifetime by ~3.8 ns. Thus, our studies discern distinct spectroscopic and structural roles for the nucleobase ligands in C4AC4TC3G, and these finding may help develop new DNA templates for other silver cluster adducts.
关键词： Nucleobase ligands,DNA,Silver clusters,Lifetime,Fluorescence,Quantum yield
更新于2025-09-23 15:21:21
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Achieving Near-Unity Photoluminescence Efficiency for Blue-violet Emitting Perovskite Nanocrystals
摘要： While the perovskite nanocrystals (NCs) have shown great promise as materials for efficient light emitting diodes (LEDs), low photoluminescence quantum yield (PLQY) of the blue-emitting perovskites is an impediment to the development of white LEDs of which blue is an essential component. Herein, we report that room temperature post-synthetic treatment of weakly blue-violet emitting (PLQY 3%) CsPbCl3 NCs with CdCl2 results in an instantaneous enhancement of the PLQY to near-unity without affecting the PL peak position (406 nm) and spectral width. The time-resolved PL and ultrafast transient absorption measurements confirm the removal of nonradiative defect states of the CsPbCl3 NCs in treated sample. The elemental composition and structural data of the treated sample reveal facile doping of Cd2+ into the crystal lattice without affecting the size and shape of the NCs. Extraordinary PLQY, high air- and photo-stability and ease of preparation of this Cd-doped CsPbCl3 make it by far the most attractive blue-emitting perovskite for development of efficient blue and white LEDs.
关键词： photoluminescence quantum yield,blue-emitting perovskites,perovskite nanocrystals,CdCl2 treatment,white LEDs
更新于2025-09-23 15:21:21
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Si, N-codoped carbon dots: preparation and application in iron overload diagnosis
摘要： Heteroatom doping is a straightforward and smart strategy to improve the fluorescence efficiency of carbon dots (CDs). We synthesized the Si, N-codoped CDs (SiNCDs) with high quantum yield up to 29.7% through one-step hydrothermal method. The linear range for Fe3+ was between 0 and 200 μM, and the limit of detection was about 5 μM, which presented potential for Fe quantification in serum to diagnose Fe overload. In addition, the SiNCDs demonstrated good selectivity to Fe3+ among high concentrations of metal ions, amino acids and H2O2, so there is no need to mix additional reagents as the colorimetric method does in clinic, making SiNCDs more competitive in clinical application. Furthermore, we explored the practicability of SiNCDs by detecting Fe in serum from five healthy volunteers and three patients suffering Fe overload. The recovery rate was from 87.1 to 113.6%, which confirmed the application prospect of SiNCDs in clinical diagnostics.
关键词： N-codoped carbon dots,hydrothermal method,Si,iron overload diagnosis,fluorescence efficiency,quantum yield
更新于2025-09-23 15:21:21
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Highly green fluorescent Nb2C MXene quantum dots
摘要： Here two dimensional Nb2C quantum dots with green fluorescence were fabricated for the first time with quantum yield (QY) up to 19%, the highest reported Nb2C dots so far with good photostability and pH stability. The S,N doping on Nb2C were considered as the main reason to enhance the high QY of Nb2C dots and was proved by the density functional theory (DFT) calculation. It was demonstrated that the fluorescent probe could be utilized effectively for 3D brain organoid labeling and embraces huge prospects in biological sensing.
关键词： green fluorescence,S,N doping,Nb2C quantum dots,3D brain organoid labeling,quantum yield
更新于2025-09-23 15:21:01
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Highly Efficient and Stable CsPbBr3 Perovskite Quantum Dots by Encapsulating in Dual-Shell Hollow Silica Spheres for WLEDs
摘要： Poor stability of CsPbX3 (X = Cl, Br or I) perovskite quantum dots (QDs) has greatly hindered their practical photoelectric applications, and how to improve it still remains a critical challenge. Herein, we encapsulated the CsPbBr3 QDs into a dual-shell hollow silica (SiO2) spheres via a simple successive ionic layer adsorption and reaction (SILAR) method. The hierarchical dual-shell structures permit CsPbBr3 QDs to be anchored on the interior of the SiO2 spheres while keeping the outside surface undisturbed, which can protect CsPbBr3 QDs from direct exposure to the atmosphere. Due to the comprehensive protection of dual-shell hollow SiO2 spheres, the CsPbBr3/SiO2 nanospheres exhibit markedly enhanced stability against light and heat, with residual PL intensity of 89% after continuous exposure of 72 h to UV light and 65% at 100?C heat treatment, respectively. In addition, an optimal PLQY of 89% is obtained with suppressed nonradiative recombination. Finally, the fabricated white light-emitting diodes (LEDs) device by employing CsPbBr3/SiO2 green phosphors could achieve a wide color gamut covering up to 136% of the NTSC standard. This work provides a novel SiO2-based encapsulation approach to solve the intrinsic instability issues of CsPbBr3 QDs, which has a profound impact on their practical applications.
关键词： photoluminescence quantum yield,CsPbBr3 quantum dots,dual-shell hollow silica spheres,stability,white light-emitting diodes
更新于2025-09-23 15:21:01
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Effect of indium alloying on the charge carrier dynamics of thick-shell InP/ZnSe quantum dots
摘要： Thick-shell InP/ZnSe III–V/II–VI quantum dots (QDs) were synthesized with two distinct interfaces between the InP core and ZnSe shell: alloy and core/shell. Despite sharing similar optical properties in the spectral domain, these two QD systems have differing amounts of indium incorporation in the shell as determined by high-resolution energy-dispersive x-ray spectroscopy scanning transmission electron microscopy. Ultrafast fluorescence upconversion spectroscopy was used to probe the charge carrier dynamics of these two systems and shows substantial charge carrier trapping in both systems that prevents radiative recombination and reduces the photoluminescence quantum yield. The alloy and core/shell QDs show slight differences in the extent of charge carrier localization with more extensive trapping observed in the alloy nanocrystals. Despite the ability to grow a thick shell, structural defects caused by III–V/II–VI charge carrier imbalances still need to be mitigated to further improve InP QDs.
关键词： indium alloying,InP/ZnSe,charge carrier dynamics,photoluminescence quantum yield,quantum dots
更新于2025-09-23 15:21:01
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Estimation of the potential for increasing the efficiency of GaInP/GaAs/Ge multi-junction solar cells by using quantum-size objects
摘要： A study of GaAs solar cells (SCs) with various quantum-sized objects has been carried out. In0.2Ga0.8As quantum wells, In0.4Ga0.6As quantum well-dots (QWDs), In0.8Ga0.2As and InAs quantum dots have been considered. The increment in photocurrent and the reduction of open-circuit voltage have been calculated using dark IV and spectral characteristics. An analytical model for estimating the efficiency of triple-junction SCs with quantum objects has been described. The calculations have shown that the optimized QWDs have a potential for increasing the efficiency of GaInP/GaAs/Ge SC from 29.8 to 30.8% (AM0, 1 sun) and from 41.6% to 43.1% (AM1.5D, 360 suns).
关键词： quantum objects,internal quantum yield,efficiency,solar cells
更新于2025-09-23 15:21:01
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Fe doped ZnO/BiVO4 heterostructure based large area, flexible, high performance broadband photodetector with ultrahigh quantum yield
摘要： Pristine ZnO has been widely explored for UV photodetectors; however it’s utility in broadband photodetectors is still an impediment due to absorbance in UV region only with low quantum efficiency and responsivity that can be accredited to high recombination rate of photo generated charge carriers. To address this issue, we report Fe metal doped 2D ZnO thin films through band gap engineering and 1D electrospun mixed inorganic monoclinic BiVO4 nanofibers heterostructure on ITO coated PET substrate based broadband photodetector (PD) with ultra-high responsivity and EQE values in comparison to PDs fabricated using expensive cleanroom techniques. BiVO4 plays the dual role of captivating photons in the visible and NIR regions and creating local electric fields at the interface of Fe doped ZnO (FZO)-BiVO4 heterostructure which helps in separation of electron-hole pairs. The robustness of the flexible PD was further examined under repeated conditions of bending cycles (upto 500) yielding stable response. The responsivity values obtained for UV, Visible and NIR lights are 7.35 A/W, 3.8 A/W and 0.18 A/W with very high EQE values of 2501.7 %, 851.2 % and 28.3 % respectively. The facile and cost-effective fabrication of the device with high performance gives a new approach for developing flexible electronics and high-performance optoelectronics devices.
关键词： Heterostructure,Broadband photodetector,Fe doped ZnO,BiVO4,ultrahigh quantum yield
更新于2025-09-23 15:21:01