Μs Lifetime Research Articles

Enzymes in a human cytoplasm model organize into submetabolon complexes

Enzyme-enzyme interactions are fundamental to the function of cells. Their atomistic mechanisms remain elusive mainly due to limitations of in-cell measurements. We address this challenge by atomistically modeling, for a total of ≈80 μs, a slice of the human cell cytoplasm that includes three successive enzymes along the glycolytic pathway: glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase (PGK), and phosphoglycerate mutase (PGM). We tested the model for nonspecific protein stickiness, an artifact of current atomistic force fields in crowded environments. The simulations reveal that the human enzymes co-organize in-cell into transient submetabolon complexes, consistent with previous experimental results. Our data both reiterate known specificity between GAPDH and PGK and reveal extensive direct interactions between GAPDH and PGM. Our simulations further reveal, through force field benchmarking, the critical role of protein solvation in facilitating these enzyme-enzyme interactions. Transient interenzyme interactions with μs lifetime occur repeatedly in our simulations via specific sticky protein surface patches, with interactions often mediated by charged patch residues. Some of the residues that interact frequently with one another lie in or near the active site of the enzymes. We show that some of these patches correspond to a general mode to interact with several partners for promiscuous enzymes like GAPDH. We further show that the non-native yeast PGK is stickier than human PGK in our human cytoplasm model, supporting the idea of evolutionary pressure to reduce sticking. Our cytoplasm modeling paves the way toward capturing the atomistic dynamics of an entire enzymatic pathway in-cell.

Palladium Catalyzed C3-(sp2)-H Alkenylation of Pyrroles via a Benzothiazole Directing Group: A Direct Access to Organic Thermally Activated Delayed Fluorescence Materials.

A Pd (II)-catalyzed direct C3-(sp2)-H alkenylation of heteroarenes using benzothiazole as a directing group was successfully achieved. A wide range of 2-N-alkylpyrroles undergo an oxidative coupling with a variety of acrylates to furnish highly regio- and chemoselective E-alkenylation products at the C3 position. An important intermediate complex has been isolated and characterized so as to have an insight into the mechanism. This convenient protocol proved to be practical to access thermally activated delayed fluorescence materials (TADF). These molecules proved to be blue-emitting TADF materials (∼ms lifetime). A detailed and systematic investigation has been carried out to study the photophysical properties, and this has been further validated by the time-dependent density functional theory calculations.

Crystallization and phase transition boosted optical linear& nonlinear and magnetic properties in transparent xCu: BaSnO3 NCs/glass-ceramic

In this study, cubic xCu: BaSnO3 (x = 0, 1, 3, and 5 mol%) perovskite nanocrystals were synthesized using a hydrothermal method. The influence of Cu doping levels on the crystal structure, morphology, size, and properties was analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Raman, Ultraviolet-Visible Spectroscopy (UV–vis), Vibrating Sample Magnetometry (VSM), and X-ray Photoelectron Spectroscopy (XPS) techniques. Across the 1–5 % doping range, the cubic BaSnO3 structure was maintained with Cu2+ in CuO6 replacing Sn4+ in the B-site. XPS analysis confirmed the formation of oxygen vacancies due to charge imbalance, leading to a decrease in optical bandgap and an increase in ferromagnetic moment. When various contents of xCu: BaSnO3 were doped into borosilicate glass, significant impacts on the glass network, crystallization, and properties were observed. Nanocrystals (∼50 nm) transitioned from cubic to orthorhombic phase beyond 3 mol% doping, modifying the glass network by converting BO3 to BO4, AlO4 to AlO6, and CuO6 to CuO4. This phase change endowed the glass's strong ferromagnetic moment and absorption due to the t2 g→eg transitions of Cu2+ in CuO6, and reduced the optical bandgap from 3.16 to 2.2 eV. The glass also exhibited improved Vickers hardness (475 HV) and a high Verdet constant of 0.174 min/G·cm due to network modifications. Glass also shows a distinct red emission at 596 nm with a 160 µs lifetime and good thermal stability, while doping levels above 3 % resulted in emission quenching. The optical nonlinear absorption coefficient and nonlinear susceptibility increased with higher doping levels, reaching huge values of α3: 5.12×10−10 m/W and χ(3): 7.52×10−10 esu, indicating potential for self-focusing applications. The increased polarizability also resulted in a high dielectric constant (18) and a large P-E loop of glasses which are promising for advanced photonics devices.

Delay sensitive and energy adaptive clustering hierarchy protocol using enhanced agglomerative hierarchy algorithm with time‐controlled jellyfish optimization

AbstractWireless sensor networks have sensing functions which made up of small sensor nodes that are processing and communication capabilities. However, the traditional approach of designating a single sensor node as the cluster head often leads to a faster depletion of its energy resources than another node. So, periodic reassignment of the cluster head role among different sensor nodes is crucial to extend operational lifetime and ensure sustained performance. Therefore, this research proposes an Enhanced Agglomerative Hierarchy Algorithm based on the Low Energy Adaptive Clustering Hierarchy (EAHALEACH) protocol, coupled with an enhanced time‐controlled optimization algorithm, to enhance energy efficiency by selecting the optimal cluster head from a candidate pool. The proposed method enhances energy efficiency by optimally selecting cluster heads, which reduces energy consumption and extends the lifespan of the network. Additionally, a lightweight energy‐aware cluster head rotation algorithm is introduced to efficiently rotate the cluster head role within the sensor node network, minimizing unnecessary data transmissions and extending the network lifetime. A hybrid approach combining Carrier Sense and Time Division Multiple Access (CSTDMA) optimizes packet forwarding by dynamically allocating time slots, reducing collisions and contention to improve packet forwarding efficiency. Comparative analysis with existing techniques demonstrates that the hybrid clustering‐based LEACH protocol achieves superior performance in terms of throughput 4600 bps by 2000 rounds, energy consumption 50 J, latency as 1 ms and network lifetime in 1000th node attains 3500 s. These advancements contribute to prolonged operational efficiency and sustained performance in wireless sensor network deployments.

Optoelectronic processes in ultrasonic spray coated organic solar cells

In this work, the role of a high boiling point green solvent additive Diphenyl ether (DPE) in device recombination processes in organic solar cell, fabricated using ultrasonic spray coating method is investigated. Without DPE and with 2.4 % DPE, the device series resistance was high of the order of 104 Ω. With 0.3 %, 0.6 %, 1.2 % DPE, series resistance was less. Transient studies show that, for these contents, the rise and decay times of photocurrent was less than 5 µs. For 0.3 % DPE, nearly 3/4th photovoltage decayed with 51.4 µs lifetime and the remaining decays with 4.6 µs lifetime. With higher DPE content (1.2 %), 97 % photovoltage decay was with a longer lifetime 46.1 µs, and remaining with 1.6 µs. With further more DPE content (2.4 %), only 1 % TPV decays with shorter lifetime of 11.6 µs and 99 % decay is in longer time scale of 672 µs. In addition, a longer lifetime of over 1000 µs was also observed for this case, indicating the presence of deep traps, in addition to the shallow traps and bimolecular recombination. Morphology studies show that for 0 % and 0.3 % DPE content, stacked structure of droplets was formed in the film, but with 0.6 % and higher content, the progressively impinging droplets intermix with each other, providing more time for the film to dry. It was shown that the contribution of trap assisted recombination for varying DPE content was due to disordered PTB7 or PC71BM phases, indicating a competition between PTB7 aggregation and PC71BM dispersion in the coated film.

Dual Luminescent Mn(II)-Doped Cu-In-Zn-S Quantum Dots as Temperature Sensors in Water.

CuInS2 quantum dots have emerged in the last years as non-toxic alternative to traditional Pb and Cd based quantum dots, especially for biological applications. In this work, the hydrothermal synthesis of alloyed Cu-In-Zn-S quantum dots (CIZS) doped with manganese(II) is explored, with different metal ratios (Mn-CIZSy). The doped quantum dots show the sensitized emission of Mn2+ (approximately ms lifetime), together with the emission of the CIZS structure (approximately µs lifetime). The relative contribution of Mn2+ emission is highly dependent on the composition of the CIZS hosting structure (In:Cu ratio). In addition to that, it is shown that Mn2+ sensitization requires a threshold energy, which suggests the involvement of an intermediate state in the sensitization mechanism. The long-lived emission intensity decay of Mn2+ shows a stable and reversible temperature response in physiological conditions (25-45°C, pH = 7.4). Mn-CIZSy quantum dots are thus interesting candidates as biological luminescent temperature probe thanks to their easy synthesis, high colloidal stability, insensitivity to dioxygen quenching and quantitative time-gated detection.

Self‐Powered Graphene/Black‐Ge Photodetectors Enhanced by Simultaneous Nanotexturing and Self‐Passivation

AbstractBlack germanium (Ge) exhibits exceptional light absorption, holding significant promise for optoelectronic applications. However, achieving self‐powered photodetection performance in black Ge is challenging due to its high surface recombination rate. Herein, this challenge is addressed by demonstrating self‐powered Graphene (Gr)/black‐Ge Schottky photodiodes, achieved through simultaneous nanotexturing and high‐quality self‐passivation. This approach involves utilizing reactive ion etching with Cl2 and BCl3 to achieve Cl‐passivated black Ge. Optical analysis reveals excellent optical characteristics in both Cl2‐treated and BCl3‐treated samples, including a high aspect ratio of 1.9 and a low reflectance of 1.5%. Notably, the Cl2‐treated black Ge exhibits a higher carrier lifetime of 20.4 µs compared to the 11.7 µs lifetime of the BCl3‐treated black Ge, attributed to the self‐passivation induced by Cl2 plasma, effectively mitigating defects. Surface composition analysis further confirms the substantial role of Cl in passivation. Significantly, these improved properties translate into notable advancements in device performance, including an enhancement in responsivity from 21 to 276 mA W−1 when compared to planar Gr/Ge devices. These findings underscore the potential of Cl2 RIE for developing high‐performance Ge‐based optoelectronic devices.

Kinetic Ensemble of Tau Protein through the Markov State Model and Deep Learning Analysis.

The ordered assembly of Tau protein into filaments characterizes Alzheimer's and other neurodegenerative diseases, and thus, stabilization of Tau protein is a promising avenue for tauopathies therapy. To dissect the underlying aggregation mechanisms on Tau, we employ a set of molecular simulations and the Markov state model to determine the kinetics of ensemble of K18. K18 is the microtubule-binding domain of Tau protein and plays a vital role in the microtubule assembly, recycling processes, and amyloid fibril formation. Here, we efficiently explore the conformation of K18 with about 150 μs lifetimes in silico. Our results observe that all four repeat regions (R1-R4) are very dynamic, featuring frequent conformational conversion and lacking stable conformations, and the R2 region is more flexible than the R1, R3, and R4 regions. Additionally, it is worth noting that residues 300-310 in R2-R3 and residues 319-336 in R3 tend to form sheet structures, indicating that K18 has a broader functional role than individual repeat monomers. Finally, the simulations combined with Markov state models and deep learning reveal 5 key conformational states along the transition pathway and provide the information on the microsecond time scale interstate transition rates. Overall, this study offers significant insights into the molecular mechanism of Tau pathological aggregation and develops novel strategies for both securing tauopathies and advancing drug discovery.

Self-channeling of a multi-Joule 10 µm picosecond pulse train through long distances in air.

In the long-wave infrared (LWIR) range, where, due to wavelength scaling, the critical power of Kerr self-focusing Pcr in air increases to 300-400 GW, we demonstrate that without external focusing a train of picosecond CO2 laser pulses can propagate in the form of a single several-centimeter diameter channel over hundreds of meters. The train of 10 µm pulses, for which the total energy ≥20 J is distributed over several near-terawatt picosecond pulses with a maximum power ≤2Pcr, is generated naturally during short pulse amplification in a CO2 laser. It is observed that the high-power 10 µm beam forms a large diameter "hot gas" channel in the ambient air with a ≥ 50 ms lifetime. Simulations of the experiment show that such filamentation-free self-channeling regime has low propagation losses and can deliver multi-Joule/TW-power LWIR pulses over km-scale distances.

Organic dopant cyclization and significantly improved RTP properties.

The internal rotation of triplet-generating molecules is detrimental to room temperature phosphorescence (RTP) radiation, and this rotation is usually mitigated by doping into rigid microenvironments. The chemical locking of internal rotation units in advance should be an effective strategy but is rarely studied in comparison. Herein, a triplet-generating molecule with two rotatable phenyls (DIA) was designed, synthesized, and then cyclized using two types of bonding bridges. We found that DIA/PMMA film shows little observable RTP afterglow despite a 148 ms lifetime, whereas carbon bridge cyclized DIA (CDIA) and oxygen bridge cyclized DIA (ODIA) emitted green and blue ultralong RTP in PMMA film, with lifetimes of 2146 ms and 2656 ms, respectively, demonstrating the potent role of pre-locking of internal rotation units in promoting RTP. Benefiting from the good spectral overlap between the RTP emissions of dopants and the absorption of perylene red (PR) in PMMA film, the almost complete triplet-to-singlet Förster resonance energy transfer was achieved under trace doping (0.1%), providing red room temperature afterglow materials with lifetimes of 1567-1800 ms. Preliminary applications of blue, green, and red afterglow materials in optical encryption and anti-counterfeiting are demonstrated. This work not only develops new triplet-generating and -radiating molecules but also introduces an effective molecular strategy for achieving ultralong RTP polymers.

Photoinduced Dynamic Ligation in Metal-Organic Frameworks.

Metal organic frameworks (MOFs), a class of porous crystalline materials consisting of metal-based nodes and organic linkers, have emerged as a promising platform for photocatalysis due to their ultrahigh functional surface area, customizable topologies, and tunable energetics. While interesting photochemistry has been reported, the related photoinduced structural dynamics of MOFs remains unclear. The consensus is that the coordination bonds between MOF nodes and linkers are considered static during photoexcitation, while the open-metal sites on the nodes are taken as the key active sites for catalysis. In this work, through a complementary time-resolved visible and infrared (IR) spectroscopic investigation, along with computational studies, we report for the first time light-induced structural bond dissociation (COO-M) and reformation in an iron-oxo framework, MIL-101(Fe). The probed excited state displayed ligand-to-metal charge transfer (LMCT) characteristics and exhibited a ca. 30 μs lifetime. The incredibly long excited-state lifetime led us to probe potential structural rearrangements that facilitated charge separation in MIL-101(Fe). By probing the vibrational fingerprints of the carboxylate linker upon LMCT photoexcitation, we observed the reversible transition of the carboxylate-Fe bond from a bidentate bridging mode to a monodentate mode, indicating the partial dissociation of the carboxylate ligand. Importantly, the bidentate configuration is recovered on the same time scale of the excited state lifetimes as probed via visible transient absorption spectroscopy. The elucidated photoinduced configurational dynamics provides a foundation for an in-depth understanding of MOF-based photocatalytic mechanisms.

Harvesting electrons and holes from photodriven symmetry-breaking charge separation within a perylenediimide photosynthetic model dimer.

Understanding how to utilize symmetry-breaking charge separation (SB-CS) offers a path toward increasingly efficient light-harvesting technologies. This process plays a central role in the first step of photosynthesis, in which the dimeric "special pair" of the photosynthetic reaction center enters a coherent SB-CS state after photoexcitation. Previous research on SB-CS in both biological and synthetic chromophore dimers has focused on increasing the efficiency of light-driven processes. In a chromophore dimer undergoing SB-CS, the energy of the radical ion pair product is nearly isoenergetic with that of the lowest excited singlet (S1) state of the dimer. This means that very little energy is lost from the absorbed photon. In principle, the relatively high energy electron and hole generated by SB-CS within the chromophore dimer can each be transferred to adjacent charge acceptors to extend the lifetime of the electron-hole pair, which can increase the efficiency of solar energy conversion. To investigate this possibility, we have designed a bis-perylenediimide cyclophane (mPDI2) covalently linked to a secondary electron donor, peri-xanthenoxanthene (PXX) and a secondary electron acceptor, partially fluorinated naphthalenediimide (FNDI). Upon selective photoexcitation of mPDI2, transient absorption spectroscopy shows that mPDI2 undergoes SB-CS, followed by two secondary charge transfer reactions to generate a PXX•+-mPDI2-FNDI•- radical ion pair having a nearly 3 µs lifetime. This strategy has the potential to increase the efficiency of molecular systems for artificial photosynthesis and photovoltaics.

Facile Synthesis and Multiple Application of Ultralong-Afterglow Room Temperature Phosphorescence Aggregate Carbon Dots from Simple Raw Materials.

Owing to the ultralong afterglow, room temperature decay phosphorescence nanomaterials have aroused enough attention. In the work, by simple one-pot solid-state thermal decomposition reaction, aggregate carbon dots (CDs) was prepared from trimesic and boric acid. Based on the intermolecular hydrogen bonds and intramolecular π-π stacking weak interaction from precursors, CDs was encapsulated in boron oxide matrix and formed aggregation. The aggregate state of CDs facilitated the triplet excited states (Tn), which could induce the room temperature decay phosphorescence properties. By careful investigation, under different excitation wavelengths at 254 and 365nm, the aggregate CDs showed > 15s and > 3s room temperature phosphorescence emission in the naked eye, which was associated with 1516.12 ms and 718.62 ms lifetime respectively. And the aggregate CDs exhibited widespread application in encoding encryption, optical anti-counterfeiting and fingerprint identification etc. The interesting aggregate CDs revealed unexpected ultralong-afterglow room temperature decay phosphorescence properties and the work opened a window for constructing ultralong-afterglow room temperature decay phosphorescence aggregate CDs nanomaterials.

Clustering-Triggered Emission Liquid Crystalline Polymer Bearing Cholesterol: Tunable Circularly Polarized Luminescence and Room-Temperature Phosphorescence.

Circularly polarized luminescence (CPL) materials with clustering-triggered emission (CTE) characteristic have gradually attracted attention for their unique photophysical properties. However, the majority of reported clusteroluminogens lack chirality and exhibit heterogeneity, making it challenging to achieve a well-defined helical structure necessary for efficient CPL with high dissymmetry factor (glum ). In this paper, chiral liquid crystals are constructed to obtain CTE-based CPL materials with high glum values. Side chain liquid crystal polymer PM6Chol bearing cholesterol clusteroluminogens are designed and synthesized. PM6Chol-coated film and PM6Chol thermal-treated film are also successfully prepared by different film-forming methods. Both the films inherit the CTE characteristic of cholesterol and show excitation wavelength-dependent luminescent behavior. However, the two polymer films exhibit different liquid crystal phase structures, with PM6Chol-coated film being a chiral bilayer smectic C phase and PM6Chol thermal-treated film being an achiral bilayer smectic A phase. Attributed to helical arrangement of cholesterol, PM6Chol-coated film emits efficient CPL with glum values up to 1.0 × 10-1 . For PM6Chol thermal-treated film, no CPL signal is detected due to the absence of helical structure. However, it shows obvious room-temperature phosphorescence with 2.0 s afterglow and 23.9ms lifetime.

A concerted ATPase cycle of the protein transporter AAA-ATPase Bcs1

Bcs1, a homo-heptameric transmembrane AAA-ATPase, facilitates folded Rieske iron-sulfur protein translocation across the inner mitochondrial membrane. Structures in different nucleotide states (ATPγS, ADP, apo) provided conformational snapshots, but the kinetics and structural transitions of the ATPase cycle remain elusive. Here, using high-speed atomic force microscopy (HS-AFM) and line scanning (HS-AFM-LS), we characterized single-molecule Bcs1 ATPase cycling. While the ATP conformation had ~5600 ms lifetime, independent of the ATP-concentration, the ADP/apo conformation lifetime was ATP-concentration dependent and reached ~320 ms at saturating ATP-concentration, giving a maximum turnover rate of 0.17 s−1. Importantly, Bcs1 ATPase cycle conformational changes occurred in concert. Furthermore, we propose that the transport mechanism involves opening the IMS gate through energetically costly straightening of the transmembrane helices, potentially driving rapid gate resealing. Overall, our results establish a concerted ATPase cycle mechanism in Bcs1, distinct from other AAA-ATPases that use a hand-over-hand mechanism.

A grid of 200 000 models of young δ Scuti stars using mesa and GYRE

ABSTRACT The rapidly increasing number of delta Scuti stars with regular patterns among their pulsation frequencies necessitates modelling tools to better understand the observations. Further, with a dozen identified modes per star, there is potential to make meaningful inferences on stellar structure using these young δ Sct stars. We compute and describe a grid of >200 000 stellar models from the early pre-main sequence (pre-MS) to roughly one-third of the MS lifetime, and calculate their pulsation frequencies. From these, we also calculate asteroseismic parameters and explore how those parameters change with mass, age, and metal mass fraction. We show that the large frequency separation, Δν, is insensitive to mass at the zero-age main sequence. In the frequency regime observed, the Δν we measure (from modes with n ∼ 5–9) differs from the solar scaling relation by ∼13 per cent. We find that the lowest radial order is often poorly modelled, perhaps indicating that the lower order pressure modes contain further untapped potential for revealing the physics of the stellar interior. We also show that different nuclear reaction networks available in mesa can affect the pulsation frequencies of young δ Sct stars by as much as 5 per cent. We apply the grid to five newly modelled stars, including two pre-MS stars each with 15+ modes identified, and we make the grid available as a community resource.

Crystal structure, optical properties, mobility, and photoelectric performance of [PEA]3[Bi2I9

Lead halide‐based salts exhibit good photoelectric properties; however, the use, leakage, and recovery of toxic lead require careful consideration. Therefore, developing a lead‐free optoelectronic material conveniently and quickly is very important. Moreover, there is relatively little research on the salts of bismuth halides. In this study, we synthesized [PEA]3[Bi2I9] single crystals (SC) by volatilizing N,N‐dimethylformamide (DMF) solvent at 70°C. The crystal system and spatial group of [PEA]3[Bi2I9] are monoclinic and P21/n, respectively. The Tauc plot reveals the optical band gap of the [PEA]3[Bi2I9] SC at 2.048 eV. The carrier mobility of [PEA]3[Bi2I9] SC is 47.4 cm2 V−1 s−1. Steady‐state fluorescence and time‐resolved fluorescence spectrum indicate that there are four fluorescence peaks and about 7 μs lifetime, respectively. The photodetector based on [PEA]3[Bi2I9] SC under different voltages (0.5, 1, 1.5, 2, and 2.5 V) exhibits stability and regularity with turning‐on/off of the light. In addition, thermogravimetric analysis (TGA) tests indicate that [PEA]3[Bi2I9] SC has considerable thermal stability at temperatures up to 260°C, showing promise for becoming a high temperature resistant and nontoxic sensor with good application prospects.

Single Molecular Persistent Room-Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol-Decorated Optically Innocent Cyclotriphosphazenes.

Circularly polarized luminescence (CPL) features of BINOL-decorated cyclotriphosphazenes (CPs) are reported for the first time. The luminescence dissymmetry factor (glum ) of these compounds in chloroform solutions and polymethyl methacrylate (PMMA) thin films with wt 1 % doping concentrations are found to be 1.0×10-3 , and 2.9×10-3 , respectively. However, no CPL signal is observed for the pristine solids. The enantiomers (CP-(R)/CP-(S)) show ultraviolet photoluminescence (~350-360 nm) in solution and the solid state. These compounds show ~10 times larger absolute photoluminescence quantum yield (PLQY) than the simple BINOLs in the solutions state. In the solid state, CP-(R) shows larger PLQY than binaphthol-(R); in contrast, the S enantiomer shows lower PLQY than binaphthol-(S); this indicates that the isomer-dependent solid-state packing of these compounds plays a crucial role in controlling the PL. Thin films with more than 1 % doping concentration and pristine solids of these compounds do not show persistent room-temperature phosphorescence (pRTP) due to concentration-caused quenching. However, thin films with wt 1 % of these chiral emitters exhibit pRTP characteristics with a ~159-343 ms lifetime under vacuum. Theoretical calculations reveal that the cyclophosphazene acts as an optically innocent dendritic core, and the optical features of these compounds are dictated by the pendent BINOL chromophore.

Baria-Silica Erbium-Doped Fibers for Extended L-Band Amplification

We present baria-silica erbium-doped fibers (Ba-EDF) for extending the bandwidth of L-band EDFAs beyond 1620 nm. Using a combination of modified chemical vapor deposition (MCVD) process and solution-doping technique, we demonstrate low loss (<10 dB/km at 1200 nm) fiber cores with BaO concentration of 1-3 mol% and Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> concentration of 8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">24</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . We show that the optical properties and EDFA performance are positively affected by increasing the BaO content. Namely, when we increase the BaO concentration from 1.3 to 3 mol%, we observe a reduction of pair-induced quenching that correlates with a bi-exponential luminescence decay with a dominant 15.5 ms lifetime component. Furthermore, the slight modifications of absorption/ emission coefficients point to a red-shift of the signal excited state absorption and consequently, to a moderate extension of the L-band gain to longer wavelengths (1622 nm).

High-speed imaging and statistics of puffing and micro-exploding droplets in spray-flame synthesis

Thermally-induced breakup of metal-precursor-laden droplets in spray-flame synthesis occurs via a rapid and disruptive disintegration, i.e., “puffing” and “micro-explosion”. To assess the temporal evolution and statistics of droplet disruption, LED-illuminated droplet shadowgraphs were imaged with a microscope onto a high-speed camera and morphological image analysis was applied. The atomized liquid was a mixture of 35 vol.-% ethanol and 65 vol.-% 2-ethylhexanoic acid mixed with iron(III) nitrate nonahydrate (INN) as a precursor. Droplet evaporation and disruption were also simulated with a population balance model. The model finds solid precipitates forming in the droplets because of the decomposition of the precursor intermediate iron(III) 2-ethylhexanoate. The precipitates form a particle shell, which favors the superheating of the droplets’ interior, and they facilitate heterogeneous bubble nucleation. Imaging experiments and modelling find that per 10 µs lifetime of a droplet, the probability for disruption increases from 5 to 13% and 5 to 19%, respectively, when increasing the INN concentration from 0.05 to 0.5 mole/l. The probability of disruption suggests that throughout their lifetime in the spray flame, nearly all droplets will undergo disruption and many of them multiple times. In the experiment, droplets before disruption are 15% smaller than regular, non-disrupting droplets. Once disrupted, the droplets have a 45% smaller mean diameter than regular droplets. Under all conditions, disrupting and disrupted droplets are slower than regular droplets while the disruption does not significantly accelerate disrupted droplets.