Fluorescence Peak Research Articles

Stepwise phosphorescence energy transfer for NIR cell imaging based on macrocycle disaggregated amphiphile

A multicolor phosphorescence supramolecular system was constructed based on the complexation of amphiphile (G) and cucurbit[8]uril (CB[8]). The guest G which was composed of hydrophobic coumarin and hydrophilic phosphor 6-bromoisoquinoline can aggregate in water and form large nanosheets accompanying bright fluorescence at 390 nm. After encapsulated by CB[8], the aggregation was prohibited and formed nanosheets with smaller size and the fluorescence peak at 390 nm decreased, meanwhile a phosphorescence peak at 550 nm appeared. Upon the adding of lower-rim dodecyl-modified sulfonatocalix[4]arene (SC4AD), the aggregation was disrupted and particles were formed which were a few 10s of nanometers in size. Subsequently, a stepwise high efficient phosphorescence energy transfer system with a variety of colors was constructed with rhodamine B (RhB) and Sulfo-Cyanine 5 (cy5)/Si-rhodamine (SiR) as acceptors. Finally, the multicolor phosphorescent supramolecular assembly was used to near-infrared cell imaging.

Fluorescent Selectivity-Enhanced FRET Based on 3D Photonic Crystals for Multianalyte Sensing.

Fluorescence resonance energy transfer (FRET) finds widespread utility in biochemical sensing, single-molecule experiments, cell physiology, and various other domains due to its inherent simplicity and high sensitivity. Nevertheless, the efficiency of energy transfer between the FRET donor and acceptor is significantly contingent on the local photonic environment, a factor that limits its application in complex systems or multianalyte detections. Here, a fluorescent selectivity-enhanced acridine orange (AO)-aflatoxins (AFs) FRET system based on a range of 3D topological photonic crystals (PCs) was developed with the aim of enhancing the selectivity and discrimination capabilities of FRET. By exploring the angle-dependent characteristics of the photonic stopband, the stopband distribution across different 3D topological PCs pixels was investigated. This approach led to selective fluorescence enhancement in PCs that matched the stopbands, enabling the successful discrimination of six distinct aflatoxins and facilitating complex multianalysis of moldy food samples. In particular, the stopband, which was strategically positioned within the blue-purple structural color range, exhibited a strong alignment with the fluorescence peaks of both the FRET donor and acceptor. This alignment allowed the 3D three-pointed star PCs to be effectively employed for the identification of mixed samples containing six distinct aflatoxins as well as the detection of real aflatoxin samples present in moldy potatoes, bread, oats, and peanuts. Impressively, this approach achieved a remarkable accuracy rate of 100%. This innovative strategy not only presents a novel avenue for developing a multitarget discrimination analysis system but also offers a convenient pretreatment method for the quantitative detection of various aflatoxins.

DFT/TDDFT based study to decipher the excited state intramolecular proton transfer process for 3-benzothiazol-2-yl-2-hydroxy-5-methyl-benzaldehyde-oxime

In this study, we theoretically investigate the interactions of hydrogen bonding in excited states and the mechanism of intramolecular proton transfer (ESIPT) for the novel compound 3-benzothiazol-2-yl-2-hydroxy-5-methyl-benzaldehyde-oxime (HBT-phos) theoretically. Herein, the effects of atomic electronegativity of chalcogen (O, S and Se) are also focused. Firstly, employing quantum theory of atoms-in-molecules (QTAIM) method, we confirm intrinsic quality of O-H···N within HBT-phos derivatives (HBT-phos-O, HBT-phos-S and HBT-phos-Se). By astutely examining changes in geometries and infrared (IR) spectra, we elegantly demonstrate O-H···N is remarkably strengthened in S1 state, indicating a pronounced tendency towards ESIPT. Computational hydrogen bonding energies further magnificently support this conclusion. Probing into photo-induced excitation, we discover heightened electronic densities surrounding N atom that play pivotal roles in attracting protons, thereby facilitating ESIPT. Ultimately, upon comparing potential energy curves in excited states, we deduce ESIPT process is expected to be exceptionally rapid with low atomic electronegativity (O → S → Se), which elucidates why detecting fluorescence peak of HBT-phos-S itself proves challenging in experiment. This study not only fills the void in understanding ESIPT mechanism within HBT-phos derivatives and authentically reveals its unambiguous mechanism, but also presents atomic-electronegativity-dependent ESIPT behaviour and the explanation for fluorescence quenching observed in prior experiment.

Synthesis, Structures and Photophysical Properties of Asymmetric Fulvene-[b]-fused BODIPYs.

Herein, we developed a one-pot procedure to synthesize novel fulvene-[b]-fused BODIPYs from α-(2-alkynylphenyl)-pyrrole and acylpyrrole, using 5-exo cyclization as the key transformation. Compared to benzene-[b]-fused BODIPYs, although they have similar chemical compositions, their structures and properties significantly differ from each other, which can be attributed to the less aromaticity of the fulvene linker than benzene. Notably, fulvene-[b]-fused BODIPY 1 b exhibits helical-twisted core skeleton, intensified red-shifted absorption, and peak fluorescence. In addition, the pathway of this one-pot reaction and the mechanism of POCl3 mediated 5-exo cyclization have been proposed by a combining experimental and computational study.

Designing of multifunctional graphene quantum dot-polyvinyl alcohol-polyglycerol luminescent film for fluorescence detection of pH in sweat

BackgroundWound infection, skin disease, renal failure, cancer, cystic fibrosis, and other pathologies may induce obvious pH changes in sweat. Thus, tracking skin pH changes can help monitor human health in a convenient manner. Owing to their biocompatibility, easy preparation, and sensitive response to pH changes, graphene quantum dots (GQDs) have received increased attention in the optical detection of pH changes. However, their poor luminescent efficiency under visible light excitation and lack of functional diversification limit their application in skin pH monitoring. Therefore, the development of GQDs with excellent ultraviolet protection ability and antibacterial and luminescence performance is essential. ResultsFolic acid-, histidine-, and serine-functionalized boron-doped graphene quantum dots (FHSB-GQDs) were designed and synthesized via thermal treatment. The resulting FHSB-GQDs exhibit strong yellow fluorescence emission under excitation with 490-nm visible light and sensitive pH responsiveness. The peak fluorescence intensity linearly decreases with increasing pH from 4 to 9. Furthermore, the FHSB-GQDs were integrated with polyvinyl alcohol and polyglycerol to form a luminescent film via hydrogen bond interactions. The film exhibits high transparency, mechanical flexibility, ultraviolet protection ability, and antibacterial activity. The presence of polyvinyl alcohol and polyglycerol restricts the free movement of the FHSB-GQDs and improves fluorescence behavior. The film was successfully applied in an intelligent pH-sensing system for monitoring pH changes in human sweat. SignificanceThe graphene quantum dot–polyvinyl alcohol–polyglycerol luminescent film offers excellent transparency, mechanical flexibility, ultraviolet protection ability, antibacterial activity, and luminescence performance. It was successfully applied in an intelligent pH sensing system for the detection of pH changes in human sweat. This study provides a new strategy for the design and construction of wearable sensing systems for health monitoring, facial masks, and medical dressings.

Stratification of dissolved organic matter in the upper 5000 m water column in the western Pacific Ocean

Marine dissolved organic matter (DOM) is a principal reservoir involved in biogeochemical cycles and exerts a pivotal influence on global carbon flux dynamics. In this study, excitation-emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) was conducted on 230 DOM samples collected from 21 sites between February and April 2022 in the Western Pacific Ocean (WPO). We identified five distinct fluorescence peaks (peaks B, T, A, C, and M), predominantly protein-like and humic-like components. These findings, marked by significant differences (p < 0.01) in fluorescence intensities and spectral indices, characterized the transformation of DOM with ocean depth, illustrating a transition from active to recalcitrant forms. Additionally, random forest analysis (RFA) identified depth as a key factor influencing marine dissolved organic carbon (DOC), with a 32.59% importance value. Correlations between hydrological and fluorescent parameters underscored the complexity of DOM sources and influencing processes. Overall, this work broadens our understanding of DOM variability in the upper 5000 m of the WPO, enhancing our knowledge of the marine environment's role in the global carbon cycle.

Investigating the effects of solvent polarity and temperature on the molecular, photophysical, and thermodynamic properties of sinapic acid using DFT and TDDFT.

Sinapic acid (SA) is widely used in cosmetics, foods, and pharmaceuticals due to its antioxidant, anti-inflammatory, neuroprotective, antimicrobial, antifungal, anticancer, and cardioprotective properties. However, environmental factors such as solvent polarity and temperature can influence its biological activity. This work determined how solvent polarity and temperature affected the molecular, photophysical, and thermodynamic properties of SA in gas and various solvents using semi-empirical (MP6), Hartree-Fock (HF) with the B3LYP method and a 6-311++G(d,p) basis set, and density functional theory (DFT) with various basis sets, such as 3TO-3G*, 3-21G+, 6-31G++G(d,p), 6-311++G(d,p), aug-CC-PVDZ, LanL2DZ, SDD, and DGD2VP. The results indicated that solvent polarity influences molecular and spectroscopic properties, such as bond angles, dihedral angles, bond lengths, FTIR spectra, solvation energy, dipole moments, HOMO-LUMO band gaps, chemical reactivity, and thermodynamic properties, resulting from interactions between the drug and solvent molecules. The findings suggested that increasing the temperature within the range of 100 to 1000 Kelvin leads to an increase in heat capacity, enthalpy, and entropy due to molecular vibrations, ultimately causing degradation and instability in SA. Furthermore, the results showed that SA underwent a redshift in the absorption peak (from 320.18 to 356.26 nm) and a shift in the fluorescence peak (from 381 to 429 nm) in the solvent phase compared to those in the gas phase. Overall, this study provides background knowledge on how solvent polarity and temperature affect the properties of SA molecules.

Dual-mode colorimetric and fluorescence detection of BRCA1 based on a CRISPR-Cas12a system.

Breast cancer, the most common malignant tumor in the world, seriously threatens human life and health. Early diagnosis of breast cancer may help enhance the survival rate. In this work, a colorimetric and fluorescent dual-mode biosensor based on the CRISPR-Cas12a system was constructed to detect the breast cancer biomarker BRCA1. The intact G4 DNA, with the assistance of K+ and hemin, catalyses the oxidation of o-phenylenediamine (OPD) with the assistance of hydrogen peroxide (H2O2), generating the oxidation product 2,3-diaminophenazine (DAP), which has distinct absorption and fluorescence peaks. The presence of the target BRCA1 activates the trans-cleavage activity of CRISPR-Cas12a, leading to the cleavage of G4 DNA and inhibiting the catalytic oxidation of OPD. Target BRCA1 was quantitatively determined by measuring both the absorbance and fluorescence intensity of DAP. The detection limits were calculated to be 0.615 nM for the colorimetric method and 0.289 nM for the fluorescence method. The dual-mode biosensor showed good selectivity and reliability for BRCA1 and can resist interference from complex substrates, and it has great potential in biomedical detection.

Exploration of the impact of graphene oxide, acetylenic gemini, and CTAT on the photophysical and aggregation properties of dipolar coumarin 153.

Advanced spectroscopic techniques have been utilized to study the interaction between the laser dye coumarin 153 (C153) and graphene oxide (GO) nanoparticles. GO was synthesized using a modified Hummers' method and characterized by UV-vis spectroscopy, Raman laser spectroscopy, FTIR-ATR spectroscopy, FESEM, HR-TEM, and XRD techniques. The GO@C153 composite was formed by mixing two aqueous solutions of GO and C153 due to their strong interaction through stacking and hydrophobic interactions. In this case, GO acts as an effective fluorescence quencher for C153 molecules, which undergo H-type aggregation in the presence of GO. The Stern-Volmer equation and time-dependent fluorescence studies were utilized to analyse the mechanism of fluorescence quenching. According to the findings, both static and dynamic quenching processes are responsible for the reduction in fluorescence intensity. The effect of surfactants (both cetyltrimethylammonium p-toluenesulfonate (CTAT) and synthesized N,N'-dihexadecyl-N,N,N',N'-tetramethyl-N,N'-but-2-ynediyl-di-ammonium chloride (16-4-16)) on the aggregation and photophysical properties of the dye was investigated using surface tensiometry, conductometry, UV-vis absorption spectroscopy, steady-state fluorescence measurements, DLS, and time-dependent fluorescence spectroscopy. Surfactants change the microenvironment of the C153 dye, leading to spectrum shifting and a higher quantum yield, which causes a rapid rise in fluorescence intensity in the micellar medium. It has been noted that in a micellar medium rather than in an aqueous one, the luminous intramolecular charge transfer (ICT) state of C153 stabilises. Lastly, we investigated the photophysical behavior of the GO-C153-micelle ternary system and discovered that, in the presence of a micellar medium, the quenched and blue-shifted (H-type aggregation) fluorescence peak of C153 (in the presence of GO) began to intensify once more. The main goal of this work is to create an effective and fairly cost powerful fluorescence sensor. Additionally, the ternary system (GO-C153-micelle) analytical idea can be employed to identify the onset of micelle formation. In wastewater treatment analysis, the GO-C153-surfactant ternary system concept can also be used to regenerate the adsorbent (in this case, GO) from dye molecules by allowing the dye molecules to exit the adsorbent and enter the micellar medium.

Effect of external electric fields on the ESDPT process and photophysical properties of 1,8-dihydroxy-2-naphthaldehyde.

In this work, by capitalizing on the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) methods, it has been systematically studied that the excited state double intramolecular proton transfer (ESDPT) process and the photophysical properties of 1,8-dihydroxy-2-naphthaldehyde (DHNA) are affected by the distinct external electric fields (EEFs). The obtained intramolecular hydrogen bond (IHB) parameters containing bond lengths and angles, as well as infrared (IR) vibrational spectra demonstrate that IHB strength changes in the distinct EEFs. Moreover, not only do the potential energy surfaces (PESs) indicate that the ESDPT process of DHNA is stepwise, but also increasing the positive EEF results in a decrease in the energy barrier accordingly, while vice versa. The absorption and fluorescence spectra also undergo a corresponding red or blue shift in the EEF; for instance, when the EEF changes from +10 × 10-4 a.u. to +20 × 10-4 a.u., the fluorescence peak undergoes a blue shift from 602 nm to 513 nm in the keto2 form. In a nutshell, the ESDPT process of DHNA can be influenced by the EEF, which will serve as a reference in regulating and controlling proton transfer that causes luminescence.

Narrowband TADF emitters with high utilization of triplet excitons: theoretical insights and molecular design.

Narrowband emitters with thermally activated delayed fluorescence (TADF) features, known as multi-resonant TADF (MR-TADF) emitters, are drawing increasing research interest owing to their properties of high efficiency and excellent color purity. However, MR-TADF-based devices often face serious efficiency roll-off at high luminance intensity, which could be attributed to undesired triplet-triplet annihilation (TTA) caused by the structural planarity and relatively small reverse intersystem crossing rate constants (krisc) of MR-TADF emitters. Herein, combining a sp3-C inserted strategy to suppress harmful bimolecular interactions and chalcogens to improve the krisc, a series of asymmetric narrowband emitters, namely, DMAC-O, DMAC-S, and DMAC-Se, have been theoretically designed to break the slow rate-limiting step of krisc of experimental BN-DMAC. For comparison, both O and Se atoms were doped into the MR skeleton to substitute two sp3-inserted units, yielding BN-O-Se. The combination of TD-DFT and the wavefunction-based STEOM-DLPNO-CCSD approach exhibits that those asymmetric molecules are promising for simultaneously exhibiting narrow emission spectral full-width at half-maximums (FWHMs) and high luminous efficiencies. The contributions of chalcogens to hole distributions result in red-shifted fluorescent peaks, and the asymmetric strategy also helps with twisted molecular configuration, which is beneficial for suppressing unfavorable TTA. Furthermore, the incorporation of chalcogens is sufficient to promote the intersystem crossing and reverse intersystem crossing channels of asymmetric emitters. More importantly, the doped heavy Se atom results in a significantly increased krisc of 2.32 × 106 s-1 for DMAC-Se, which is more than 200 times larger than 1.09 × 104 s-1 of pristine BN-DMAC. These results suggest that the combination of the heavy Se atom and an sp3-inserted unit is a feasible strategy for achieving poor planarity and significantly enhancing krisc, which will help in harvesting triplet excitons, thereby inhibiting efficiency roll-off in corresponding narrowband devices.

The blue shift of fluorescence emission reveals the dsRNA-loading capacity of cationic nanocarriers.

The loading capacity of dsRNA by nanocarriers is a key parameter in the process of RNAi commercialisation. In this research, a sustainable, simple, and cheap method was developed to determine the dsRNA loading capacity by popular cationic nanocarriers. In this method, the fluorescence emission of the cationic nanocarrier + (dsRNA-DAPI) shows blue shift in comparison to that of dsRNA-DAPI. When dsRNA-DAPI is completely loaded by cationic nanocarriers, the fluorescence peak coincides with the emission wavelength of DNA-DAPI. The samples of nanocarrier + (dsRNA-DAPI) are simply tested in a fluorometer with no damage to the samples. The reported method is simpler, cheaper, and more sustainable than gel electrophoresis and HPLC, and will fulfill the industry need for reliable and quick quality administration/control in the production process.

Mineral oil emulsion species and concentration prediction using multi-output neural network based on fluorescence spectra in the solar-blind UV band.

The accurate monitoring of oil spills is crucial for effective oil spill recovery, volume determination, and cleanup. Oil slicks become emulsified under the effects of wind and waves, which increases the consistency of the oil spills. This phenomenon makes oil spills more challenging to handle and exacerbates environmental pollution. In this study, the variation of the solar-blind ultraviolet (UV) fluorescence spectra obtained from simulated oil spills with different oil types and oil-water ratios was investigated. By designing and constructing a multi-angle excitation and detection system, an apparent fluorescence peak of the oil emulsions was observed at around 290 nm under 220 nm excitation. By utilizing competitive adaptive reweighted sampling (CARS) and multi-output neural network algorithms, both the types and concentrations of the emulsified oils were obtained simultaneously. The classification accuracy for identifying the oil type exceeds 98%, and the mean absolute percentage error (MAPE) for concentration regression is around 2%. The results indicate that active solar-blind UV fluorescence could become a supplementary method for on-site oil spill detection to achieve comprehensive monitoring of oil spills. This study provides potential applications for UV-induced fluorescence spectrometry in oil spill on-site monitoring during the daytime.

A one-step process for multi-gradient wettability modification on a polymer surface.

The surface modification technique is applied in microfluidic devices to modify wettability and achieve different flow velocities. Currently available methods for poly(dimethylsiloxane) (PDMS) surfaces may reliably induce wettability changes, but only one area can be altered at a time. This work introduces the controlled gradient oxygen plasma modification (CGPM) technique, which layers several resin masks with varying porosities on top of the PDMS surface. Selective wettability of the PDMS surface can be achieved by varying the oxygen plasma density above the modified material's surface by manipulation of the porosity value. Through the implementation of the COMSOL plasma module, the impact of the mask's porosity, through-hole size, distribution, and distance from the PDMS surface on wettability was studied. The suggested CGPM approach was characterized by contact angle measurements. During the 25-second CGPM procedure, the PDMS surface's contact angle continually changed from 8.77° to 76.98°. An integrated microfluidic device was created and manufactured to identify D-dimers to illustrate this method. In comparison with standard oxygen plasma treatment, the D-dimer assay was finished in 10 minutes and had a dynamic range of 1-1000 ng mL-1, with a peak fluorescence signal augmentation of 78.3% and an average fluorescence intensity enhancement of 31.1%.

Application of the k-Means Algorithm and the Gaussian Mixture Model (GMM) – African Vulture Optimization Algorithm (AVOA) for the Resolution of Overlapping Energy-Dispersive X-Ray Fluorescence (EDXRF) Peaks

Limitations in instrument resolution mean that soil samples analysis using energy-dispersive X-ray fluorescence (EDXRF) often produced overlapping spectral peaks of heavy metals with similar energies. This overlapping of spectral peaks posed a significant problem in the quantitative analysis of heavy metals in soil samples. Therefore, it was necessary to decompose the overlapping peaks. In this paper, a new method for decomposing overlapping peaks was presented in the context of Gaussian Mixture Model (GMM) parameter estimation, combining the k-means algorithm and the African Vulture Optimization Algorithm (AVOA). The data acquired from EDXRF instruments were preprocessed before being input to the k-means algorithm, which produces the output used to initialize the parameters of the GMM. Subsequently, AVOA was employed to optimize the GMM parameters based on a fitness function derived from the data. Ultimately, the optimized GMM parameters obtained through the AVOA process yield the optimal solution for the decomposition of overlapping peaks. This approach effectively addressed the challenge of peak overlap in the determination of heavy metals in soil by EDXRF. Soil samples were obtained from national standard samples, peach gardens, and vegetable-growing regions. The results showed that the maximum absolute errors for the peak channel and peak area were 1.46% and 6.37%, respectively. A comparison of the proposed model with others models indicated that the k-means-GMM-AVOA model exhibits the best performance in terms of speed, accuracy, and stability.

A magnetic molecular imprinting-based fluorescence probe for sensitive and selective detection of 2,4-D herbicide.

A new magnetic molecular imprinting-based turn-on fluorescence probe (Fe3 O4 NPs@SiO2 @NBD@MIPs) has been synthesized via a facile sol-gel polymerization for the detection of 2,4-dichlorophenoxyacetic acid (2,4-D). Based on the photoinduced electron transfer (PET) of nitrobenzoxadiazole (NBD), 2,4-D can be recognized by enhancement of NBD fluorescence. With the presence of Fe3 O4 in the core of the probe, this sensor can also be reused many times using magnetic aggregation methods. After the addition of various concentrations of 2,4-D, the fluorescence peak at 530 nm (excitation of 468 nm) increased linearly ranging from 0.1 to 3μM with a detection limit of 0.023 μM. This sensing system is believed to be available for detecting 2,4-D in real samples, with high recovery rates ranging from 94% to 108% for three spike levels of 2,4-D with precisions below 5%.

Ratiometric fluorescent and electrochemiluminescent dual modal assay for detection of 2,6-pyridinedicarboxylic acid as an anthrax biomarker

2,6-pyridinedicarboxylic acid (DPA) is an excellent biomarker of Bacillus anthracis (B. anthracis). The sensitive detection of DPA, especially through visual point-of-care testing, was significant for accurate and rapid diagnosis of anthrax to timely prevent anthrax disease or biological terrorist attack. Herein, a ratiometric fluorescent (R-FL) and electrochemiluminescent (ECL) dual-mode detection platform with a lanthanide ion-based metal-organic framework (Ln-MOF, i.e., M/Y-X: M = Eu, Y = Tb, and X = 4,4′,4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid) was developed. Eu/Tb-TATAB nanoparticles were constructed to identify DPA. The R-FL detection platform quantitatively detected DPA by monitoring the I545/I617 ratio of the characteristic fluorescence peak intensities of Tb3+ ions and Eu3+ ions. The ECL sensing platform successfully quantified DPA by exploiting the burst effect of DPA on the ECL signal. The above methods had highly sensitive and rapid detection of DPA in water and serum samples. The results showed that this dual-mode detection platform may be projected to be a powerful instrument for preventing related biological warfare and bio-terrorism.

Excited-state proton transfer based fluorescence in Kaempferol powder and solutions with different concentrations

Kaempferol (KMP) is one of the most common flavonoids, currently being extensively studied for its numerous beneficial health effects. Here we study the fluorescence (FL) emission of KMP powder and of its solutions prepared using different types of solvents (polar and non-polar). In the spectra of KMP powder and KMP solutions with high concentration, the same FL peak with maximum at 1.9 eV is observed. Another FL peak, at higher energy of 2.45 eV, emerges in solutions, its relative intensity increases with decreasing solution concentration. The FL emission of solutions with lowest concentration displays only that peak. To calculate characteristic energies of absorption and emission of KMP molecule in vacuum and in solutions we use time-dependent density functional theory. Comparing the results of computations with measured FL spectra, we associate the FL band at 1.9 eV with the emission due to excited state intramolecular transfer of the proton of –OH5 hydroxyl group. The FL emission at 2.45 eV is related to the –OH3 proton transfer. We measure the FL spectra of KMP powder using two different excitation energies, 3.06 eV and 2.33 eV, and find that its FL spectrum depends on the excitation energy. To understand that dependence, we compare the FL spectra of KMP and Q monohydrate powders. We consider the excited state intermolecular transfer of the proton from –OH3′ hydroxyl group to a neighboring molecule in Q crystal and calculate the energy corresponding to the emission of the resulted anion of Q molecule. The spectral feature at 1.69 eV observed only in the FL spectrum of Q hydrate is attributed to the Q anion FL emission.

Scintillation properties of (Ph4P)2ZnX4 (X = Cl, Br)

We fabricated (Ph4P)2ZnCl4 and (Ph4P)2ZnBr4 crystals (Ph4P: tetraphenylphosphonium) with zero-dimensional structures via solvent evaporation and evaluated their optical and scintillation properties. Fluorescence and phosphorescence peaks derived from Ph4P+ cations appeared at 345 and 510 nm, respectively, for both crystals, while an emission originating from self-trapped excitons was also detected for (Ph4P)2ZnBr4. In the scintillation spectra, both samples exhibited a phosphorescence peak, while a weak fluorescence peak was also observed for (Ph4P)2ZnCl4. In addition, the scintillation light yield (LY) was determined by pulse-height spectra with 1 μs shaping time. A pulse-height peak was observed from (Ph4P)2ZnCl4, and the scintillation LY was about 670 photons/5.5 MeV-α, which was higher than that of a ZnO single crystal.

Mapping particulate organic carbon in lakes across China using OLCI/Sentinel-3 imagery

Remote sensing monitoring of particulate organic carbon (POC) concentration is essential for understanding phytoplankton productivity, carbon storage, and water quality in global lakes. Some algorithms have been proposed, but only for regional eutrophic lakes. Based on in-situ data (N = 1269) in 49 lakes across China, we developed a blended POC algorithm by distinguishing Type-I and Type-II waters. Compared to Type-I, Type-II waters had higher reflectance peak around 560 nm (>0.0125 sr−1) and mean POC (4.65 ± 4.11 vs. 2.66 ± 3.37 mg/L). Furthermore, because POC was highly related to algal production (r = 0.85), a three-band index (R2 = 0.65) and the phytoplankton fluorescence peak height (R2 = 0.63) were adopted to estimate POC in Type-I and Type-II waters, respectively. The novel algorithm got a mean absolute percent difference (MAPD) of 35.93 % and outperformed three state-of-the-art formulas with MAPD values of 40.56–76.42 %. Then, the novel algorithm was applied to OLCI/Sentinel-3 imagery, and we first obtained a national map of POC in 450 Chinese lakes (> 20 km2), which presented an apparent spatial pattern of “low in the west and high in the east”. In brief, water classification should be considered when remotely monitoring lake POC concentration over a large area. Moreover, a process-oriented method is required when calculating water column POC storage from satellite-derived POC concentrations in type-II waters. Our results contribute substantially to advancing the dynamic observation of the lake carbon cycle using satellite data.