Aqueous secondary organic aerosol formation from the direct photosensitized oxidation of vanillin in the absence and presence of ammonium nitrate

Vanillin (VL), a phenolic aromatic carbonyl abundant in biomass burning emissions, forms triplet excited states (3VL∗) under simulated sunlight leading to aqueous secondary organic aerosol (aqSOA) formation. Nitrate and ammonium are among the main components of biomass burning aerosols and cloud or fog water. Under atmospherically relevant cloud and fog conditions, solutions composed of either VL only or VL with ammonium nitrate were subjected to simulated sunlight irradiation to compare aqSOA formation via the direct photosensitized oxidation of VL in the absence and presence of ammonium nitrate. The reactions were characterized by examining the VL decay kinetics, product compositions, and light absorbance changes. Both conditions generated oligomers, functionalized monomers, and oxygenated ring-opening products, and ammonium nitrate promoted functionalization and nitration, likely due to its photolysis products (⚫OH, ⚫NO2, and NO2- or HONO). Moreover, a potential imidazole derivative observed in the presence of ammonium nitrate suggested that ammonium participated in the reactions. The majority of the most abundant products from both conditions were potential brown carbon (BrC) chromophores. The effects of oxygen (O2), pH, and reactants concentration and molar ratios on the reactions were also explored. Our findings show that O2 plays an essential role in the reactions, and oligomer formation was enhanced at pH <4. Also, functionalization was dominant at low VL concentrations, whereas oligomerization was favored at high VL concentrations. Furthermore, oligomers and hydroxylated products were detected from the oxidation of guaiacol (a non-carbonyl phenol) via VL photosensitized reactions. Last, potential aqSOA formation pathways via the direct photosensitized oxidation of VL in the absence and presence of ammonium nitrate were proposed. This study indicates that the direct photosensitized oxidation of VL may be an important aqSOA source in areas influenced by biomass burning and underscores the importance of nitrate in the aqueous-phase processing of aromatic carbonyls.

Scintillation Response Enhancement in Nanocrystalline Lead Halide Perovskite Thin Films on Scintillating Wafers

Lead halide perovskite nanocrystals of the formula CsPbBr3 have recently been identified as potential time taggers in scintillating heterostructures for time-of-flight positron emission tomography (TOF-PET) imaging thanks to their ultrafast decay kinetics. This study investigates the potential of this material experimentally. We fabricated CsPbBr3 thin films on scintillating GGAG:Ce (Gd2.985Ce0.015Ga2.7Al2.3O12) wafer as a model structure for the future sampling detector geometry. We focused this study on the radioluminescence (RL) response of this composite material. We compare the results of two spin-coating methods, namely the static and the dynamic process, for the thin film preparation. We demonstrated enhanced RL intensity of both CsPbBr3 and GGAG:Ce scintillating constituents of a composite material. This synergic effect arises in both the RL spectra and decays, including decays in the short time window (50 ns). Consequently, this study confirms the applicability of CsPbBr3 nanocrystals as efficient time taggers for ultrafast timing applications, such as TOF-PET.

Unveiling charge dynamics of visible light absorbing oxysulfide for efficient overall water splitting

Oxysulfide semiconductor, Y2Ti2O5S2, has recently discovered its exciting potential for visible-light-induced overall water splitting, and therefore, imperatively requires the probing of unknown fundamental charge loss pathways to engineer the photoactivity enhancement. Herein, transient diffuse reflectance spectroscopy measurements are coupled with theoretical calculations to unveil the nanosecond to microsecond time range dynamics of the photogenerated charge carriers. In early nanosecond range, the pump-fluence-dependent decay dynamics of the absorption signal is originated from the bimolecular recombination of mobile charge carriers, in contrast, the power-law decay kinetics in late microsecond range is dominated by hole detrapping from exponential tail trap states of valence band. A well-calibrated theoretical model estimates various efficiency limiting material parameters like recombination rate constant, n-type doping density and tail-states parameters. Compared to metal oxides, longer effective carrier lifetime ~6 ns is demonstrated. Different design routes are proposed to realize efficiency beyond 10% for commercial solar-to-hydrogen production from oxysulfide photocatalysts.

Luminescence decay kinetics as a tool for quality control of polymer materials used in railway transport

Protective coatings and composite materials based on polymer materials are widely used. They are used in construction, railway, water and air transport to protect various structures from the harmful effects of the environment. In order to create new materials with greater strength and durability, the research related to the development of methods for controlling their quality and the formation processisneeded.The luminescence of chromophores (molecules capable of luminescence) attached to polymer molecules (polymer chains) is an effective tool for this control. The paper discusses the effect of the polymer chain size and the nature of the interaction of its units on the chromophores’ luminescence decay kinetics.

Analysis of Fluorescence Decay Kinetics of Indocyanine Green Monomers and Aggregates in Brain Tumor Model In Vivo

Spectroscopic approach with fluorescence time resolution allows one to determine the state of a brain tumor and its microenvironment via changes in the fluorescent dye’s fluorescence lifetime. Indocyanine green (ICG) is an acknowledged infra-red fluorescent dye that self-assembles into stable aggregate forms (ICG NPs). ICG NPs aggregates have a tendency to accumulate in the tumor with a maximum accumulation at 24 h after systemic administration, enabling extended intraoperative diagnostic. Fluorescence lifetime analysis of ICG and ICG NPs demonstrates different values for ICG monomers and H-aggregates, indicating promising suitability for fluorescent diagnostics of brain tumors due to their affinity to tumor cells and stability in biological tissue.

Ultrafast Quenching of Excitons in the ZnxCd1-xS/ ZnS Quantum Dots Doped with Mn2+ through Charge Transfer Intermediates Results in Manganese Luminescence

For the first time, a specific time-delayed peak was registered in the femtosecond transient absorption (TA) spectra of ZnxCd1-xS/ZnS (x~0.5) alloy quantum dots (QDs) doped with Mn2+, which was interpreted as the electrochromic Stark shift of the band-edge exciton. The time-delayed rise and decay kinetics of the Stark peak in the manganese-doped QDs significantly distinguish it from the kinetics of the Stark peak caused by exciton–exciton interaction in the undoped QDs. The Stark shift in the Mn2+-doped QDs developed at a 1 ps time delay in contrast to the instantaneous appearance of the Stark shift in the undoped QDs. Simultaneously with the development of the Stark peak in the Mn2+-doped QDs, stimulated emission corresponding to 4T1-6A1 Mn2+ transition was detected in the subpicosecond time domain. The time-delayed Stark peak in the Mn2+-doped QDs, associated with the development of an electric field in QDs, indicates the appearance of charge transfer intermediates in the process of exciton quenching by manganese ions, leading to the ultrafast Mn2+ excitation. The usually considered mechanism of the nonradiative energy transfer from an exciton to Mn2+ does not imply the development of an electric field in a QD. Femtosecond TA data were analyzed using a combination of empirical and computational methods. A kinetic scheme of charge transfer processes is proposed to explain the excitation of Mn2+. The kinetic scheme includes the reduction of Mn2+ by a 1Se electron and the subsequent oxidation of Mn1+ with a hole, leading to the formation of an excited state of manganese.

Altering the distribution of excited-state lifetimes in aminated GFP chromophores by Ag nanohole arrays

Fluorescence of the modified GFP chromophore diethyl-ABDI-BF2 dispersed in PMMA matrix is studied on top of glass, continuous and perforated optically thin silver films. In polymer, the fluorescence decay kinetics becomes non-exponential and can be described by the distribution of rate constants. The results demonstrate shortening of the excited state lifetime in the presence of silver and broadening of the lifetime distribution caused by the nanoholes.

Gd-admixed (Lu,Gd)AlO3 single crystals: breakthrough in heavy perovskite scintillators

We report a breakthrough concept for a bulk single crystal as a heavy aluminum perovskite scintillator, where due to bandgap engineering by a balanced Gd admixture in a Lu cation sublattice, the scintillation performance dramatically increases. In an optimized composition of (Lu, Gd)AlO3:Ce (LuGdAP:Ce), the light yield approaches 21,000 phot/MeV, which is close to that of classical but much less dense YAP:Ce and 50% higher than the best LuYAP:Ce reported in the literature. Moreover, contrary to LuYAP:Ce, the LuGdAP host maintains a high effective atomic number close to that of LuAP:Ce (Zeff = 64.9), which is comparable to commercial LSO:Ce. An enormous decrease in afterglow on the millisecond time scale and acceleration in the rise time of the scintillation response further increase the application potential of the LuGdAP host. The related acceleration of the transfer stage in the scintillation mechanism due to diminishing electron trap depths is proven by thermally stimulated luminescence (TSL). Furthermore, we quantitatively characterize and model the energy transfer processes that are responsible for the change in the photoluminescence and scintillation decay kinetics of Ce3+ in the LuGdAP matrix. Such an innovative (Lu, Gd)AP:Ce scintillator will become competitive for use in applications that require heavy, fast, and high light yield bulk scintillators.

Dynamic FRET-FLIM based screening of signal transduction pathways

Fluorescence Lifetime Imaging (FLIM) is an intrinsically quantitative method to screen for protein–protein interactions and is frequently used to record the outcome of signal transduction events. With new highly sensitive and photon efficient FLIM instrumentation, the technique also becomes attractive to screen, with high temporal resolution, for fast changes in Förster Resonance Energy Transfer (FRET), such as those occurring upon activation of cell signaling. The second messenger cyclic adenosine monophosphate (cAMP) is rapidly formed following activation of certain cell surface receptors. cAMP is subsequently degraded by a set of phosphodiesterases (PDEs) which display cell-type specific expression and may also affect baseline levels of the messenger. To study which specific PDEs contribute most to cAMP regulation, we knocked down individual PDEs and recorded breakdown rates of cAMP levels following transient stimulation in HeLa cells stably expressing the FRET/FLIM sensor, Epac-SH189. Many hundreds of cells were recorded at 5 s intervals for each condition. FLIM time traces were calculated for every cell, and decay kinetics were obtained. cAMP clearance was significantly slower when PDE3A and, to a lesser amount, PDE10A were knocked down, identifying these isoforms as dominant in HeLa cells. However, taking advantage of the quantitative FLIM data, we found that knockdown of individual PDEs has a very limited effect on baseline cAMP levels. By combining photon-efficient FLIM instrumentation with optimized sensors, systematic gene knockdown and an automated open-source analysis pipeline, our study demonstrates that dynamic screening of transient cell signals has become feasible. The quantitative platform described here provides detailed kinetic analysis of cellular signals in individual cells with unprecedented throughput.