Maximum Emission Peak Research Articles

Inner-filter effect based fluorescence-quenching immunochromotographic assay for sensitive detection of aflatoxin B1 in soybean sauce

A fluorescence-quenching immunochromotographic assay (ICA) was developed for sensitive detection of aflatoxin B1 (AFB1) in soybean sauce based on the inner filter effect (IFE) between flower-like gold nanoparticles (AuNFs) and quantum dots (QDs). QDs were sprayed on the test and control line zones as background fluorescence signals, whereas AuNFs were designed as the fluorescence absorber of QDs because the surface plasma resonance peak of AuNFs totally matched with the maximum emission peak of QDs. Under the optimal conditions, the fluorescence-quenching ICA strip showed a good linear detection for AFB1 in standard AFB1 solution from 0.008 μg/L to 1 μg/L with a low detection limit of 0.004 μg/L. The average recoveries for different concentrations of AFB1-spiked soybean sauce samples ranged from 84.69% to 120.44% with a coefficient of variation ranging from 2.73% to 10.41%. In addition, the reliability of the proposed method was further confirmed by ultra-performance liquid chromatography with fluorescence detection method. In brief, this novel IFE-based strip offers a simple, rapid, sensitive, and accurate strategy for quantitative detection of AFB1 in soybean sauce.

New insights into oximic ligands: Synthesis and characterization of 1D chains by the use of pyridine 2-amidoxime and polycarboxylates

The initial study of the ligand blend pyridine-2-amidoxime (pyaoxH2)/1,4-benzenedicarboxylic (H2bdc) or 1,3,5-benzenetricarboxylic acid (H3btc) provided access to four 1D coordination polymers, [Zn(bdc)(pyaoxH2)(DMF)]n (1), {[Ni(bdc)(pyaoxH2)2]·2DMF}n (2·2DMF), {[Mn(bdc)(pyaoxH2)2]·2DMF}n (3·2DMF) and [Ni(Hbtc)(pyaoxH2)2]n (5), and the discrete (0D) compound [Ni(H2btc)2(pyaoxH2)2]·2H2O (4·2H2O), whose further polymerization yielded 5. These compounds are the first metal coordination polymers bearing pyaoxH2 and rare examples of such species with any type of a 2-pyridyl oxime. The crystal structures of the compounds have been determined by single crystal X-ray crystallography, whereas their identity, purity and stability were confirmed by pxrd studies. Thermal stability studies were performed in 1, 2·2DMF, 4·2H2O and 5. The photoluminescence properties of 1 have been studied and revealed a maximum emission peak at 440 nm and a visible shoulder at 467 nm, assigned to the pyaoxH2 and bdc2− ligands, respectively.

Highly sensitive and selective detection of Fe3+ by utilizing carbon quantum dots as fluorescent probes

The carbon quantum dots (CDs) based on carbonization of citric acid and tris(hydroxymethyl)aminomethane (Tris) in glycerinum as fluorescent probes for highly sensitive and selective detection of Fe3+ have been developed. The obtained CDs exhibit an excitation-dependent fluorescence behavior. The most intense fluorescence appears under 340 nm excitation and has a maximum emission peak at 414 nm. The CDs can keep good fluorescence intensity in a wide pH values from 2 to 11. The CDs can be used as highly sensitive and selective detection fluorescent probe of Fe3+, even in real sample analysis the CDs fluorescent probes can be used.

Synthesis, photophysical and electrochemical properties of a blue emitter with binaphthalene and carbazole units

A blue emitter, 3,3′-(2,2′-dimethoxy-[1,1′-binaphthalene]-6,6′-diyl)bis(9-benzyl-9H-carbazole), was synthesized by Suzuki coupling reaction. The photophysical properties of the emitter in solution were firstly investigated by UV–Vis absorption and fluorescence emission techniques. The results indicate that the emitter has excellent optical and electron transfer properties. The maximum absorption and emission peaks of the emitter are 302 nm and 406 nm with 67.4% fluorescence quantum yield in chloroform, respectively. Thermal stability study reveals that the emitter has a good thermal stability (Td > 330 °C, Tg > 160 °C). Electrochemical Redox properties of the emitters were measured by cyclic voltammetry, and the energy gaps of highest occupied molecular orbital and the lowest unoccupied molecular orbital levels are in good agreement with the results of theoretical calculation. Furthermore, the multilayer electrochemcial device with the emitter was fabricated and its properties were explored. The wavelength of electroluminescence for the device with this emitter locates at 428 nm. These results indicate the emitter as a deep blue-emitting material has promising application in organic light-emitting diode devices.

P‐179: Color Tunable Thermally Activated Delayed Fluorescence Emitters with Changing Electron Withdrawing Characteristic of Acceptor

A series of thermally activated delayed fluorescence (TADF) emitters of 2,2′,2″‐(1,3,5‐triazine‐2,4,6‐triyl)tris(N,N‐diphenylaniline) (TPA‐Trz) , 2,2′,2″‐(pyrimidine‐2,4,6‐triyl)tris(N,N‐diphenylaniline) (TPA‐Pyr) , 2,2′,2″‐(pyridine‐2,4,6‐triyl)tris(N,N‐diphenylaniline) (TPA‐Py) are synthesized. Photophysical and electrical properties of TADF emitters were characterized according to the electron withdrawing strength of the molecule, by integrating triphenylamine electron donating unit and triazine, pyrimidine, pyridine electron withdrawing unit. Energy bandgap between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) was controlled by changing the electron withdrawing strength of electron accepting unit of the molecule. Triazine based molecule TPA‐Trz (0.12 eV) showed smallest ΔEST value than TPA‐Pyr (0.25 eV) and TPA‐Py (0.27 eV), and the maximum photoluminescence emission peak of TPA‐Trz, TPA‐Pyr, and TPA‐Py was 516, 470 and 441nm, respectively. TPA‐Trz device showed maximum external quantum efficiency of 19.7% with a CIE color coordinate of (0.30, 0.61) and TPA‐Pyr showed maximum external quantum efficiency of 13.9% with a CIE color coordinate of (0.16, 0.30).

Response of the denitrifier community and its relationship with multiple N2O emission peaks after mature compost addition into dairy manure compost with forced aeration

Animal manure is a source of the greenhouse gas nitrous oxide (N2O), therefore understanding the mechanisms underlying its production is essential for developing mitigating strategies and sustainable livestock production system. In this study, microbial communities potentially involved in multiple emission peaks during initial stage of laboratory-scale dairy manure composting with forced aeration system were investigated. Mature compost was used for the bulking agent. Change of overall bacterial community and nitrification-denitrification gene abundance were monitored by using 16S rRNA gene amoA, nirS, nirK or nosZ genes, respectively. Three N2O emission peaks were observed when the temperature reached at 45, 60 and 72 °C, at the same timing of oxygen consumption peaks. The maximum N2O emission peak was 3.86 mg h−1 kg−1 TS when the temperature reached at 60 °C. The shift of bacterial community among these experimental periods was significant, orders Flavobacteriales, Burkholderiales and Xanthomonadales increased, while orders belong to Bacillales, Lactobacillales, Clostridiales and Bacteroidales decreased. In addition, abundance of two denitrification genes (nirS and nosZ) significantly increased during this period. Clone library analysis of these genes showed that significantly increased sequences belonged to Pseudomonas-like clusters for both genes, indicates that denitrifiers possesses these genes are involved for these N2O emission peaks caused by mature compost addition.

Self-accelerated electrochemiluminescence emitters of Ag@SnO2 nanoflowers for sensitive detection of cardiac troponin T

Metal oxide semiconductor nanocrystals (NCs), which emerged as a novel class of electrochemiluminescence (ECL) emitters with low cost and good biocompatibility, have attracted particular research interests in ECL biosensors. However, their analytical applications still remained a substantial challenge of relatively low ECL intensity. Herein, the novel self-accelerated ECL emitters of silver nanoparticles functionalized SnO2 nanoflowers (Ag@SnO2 NFs) were first prepared by in situ generating silver nanoparticles on the surface of SnO2 nanoflowers via silver mirror reaction, which exhibited high-intensity ECL emission with the maximum emission peak at 542 nm in the case of S2O82− as a co-reactant. It was worthy to note that compared with traditional ECL emitters of SnO2 NCs with diameters below 10 nm, the obtained Ag@SnO2 NFs with diameters about 1–2 μM showed a stronger ECL emission. The ECL enhancement was supposed to derive from 1) the strong size effect of flower-like nanostructure aggregating by ultrathin SnO2 nanosheets, which would offer large amount of tin interstitials or oxygen vacancies; 2) the in situ generated silver nanoparticles (Ag NPs) as co-reaction accelerator, which would generate more oxidizing intermediate (▪) to significantly self-promote the ECL emission of Ag@SnO2 NFs. Given these attributes, we developed a sensitive ECL immunosensor for the detection of cardiac troponin T (cTnT) utilizing Ag@SnO2 NFs as efficient signal probes, which showed outstanding sensitivity with a favorable linear range from 1 fg/mL to 100 pg/mL and relatively low detection limit of 0.11 fg/mL. This work efficiently offered insights into the promising applications of Ag@SnO2 NFs as a low toxicity and superior ECL emitter in ECL bioanalysis.

Crystal growth, structure and characterization of Er6B4O15 as self-activated eye-safe laser material within the near-infrared waveband.

A new rare-earth borate Er6B4O15 was synthesized by a solid-state reaction technique. The crystal was obtained by a flux method. Single-crystal X-ray diffraction analysis revealed that the crystal structure is composed of ErO6 polyhedra sharing edges and BO3 groups. The absorption, near-infrared fluorescence spectra and the fluorescence decay curve of Er: 4I13/2 energy level in the Er6B4O15 crystal were measured at room temperature. The absorption peak was located at 977 nm with absorption cross section of 1.16 × 10-21 cm2 and a full width at half-maximum (FWHM) of 16 nm, which is very suitable for commercial 980 nm laser diode pumping. A maximum emission peak at 1560 mm with a broad FWHM of 64 nm was observed in this crystal because of the Er3+ transition 4I13/2→4I15/2, while the emission cross section was calculated to be 8.53 × 10-20 cm2. These results imply that the Er6B4O15 crystal is a promising candidate material for the achievement of an eye-safe near-infrared wavelength laser.

Design, characterization and nonlinear optical properties of coumarin appended chalcones: Use of a dual approach

In present investigation, we present designing and characterization of coumarin appended chalcone hybrids using a dual approach consisting of experimental and computational techniques. For the first time, the parent compound 2 ((E)-2-(3-(2,4-dimethoxyphenyl)acryloyl)-3H-benzo[f]chromen-3-one) is successfully synthesized in our lab. The compound 2 is characterized experimentally as well as quantum computational techniques. The results of absorption and emission spectra are compared with those of computationally calculated spectra. A good agreement is found among the experimental and calculated spectra of compound 2. The experimental absorption spectra show maximum absorption and emission peaks at 392 and 461 nm, which are found to be in agreement with their experimental absorption and emission peaks at 393 and 501 nm, respectively. Additionally, we perform analysis of its nonlinear optical (NLO) properties by calculating its second-(β) and third-order <γ> nonlinear polarizabilities. The compound 2 shows reasonably good NLO response with its β and <γ> amplitudes mounting to 120.23 × 10−30 esu and 677.12 × 10−36 esu, respectively. These β and <γ> amplitudes of compound 2 are ∼6 and ∼20 times larger than those of para-nitroaniline (PNA) at BMK/6-311G** level of theory. Based on above structure-property relationship, we also check the effect of substitution of donor groups in the form of further four derivatives i.e. 2a, 2b, 2c and 2d. Interestingly, among these derivatives, the derivative 2d shows a robust NLO response with its β and <γ> amplitudes as large as 218.84 × 10−30 esu and 1515 × 10−36 esu, respectively. The present investigation not only reports the first synthesis of compound 2 but also explores the potential of compound 2 and its derivatives as efficient NLO-phores.

Luminescent detection by coordination polymers derived from a pre-organized heterometallic carboxylic building unit

A tetranuclear heterometallic complex [Li2Zn2(piv)6(py)2] (piv− = pivalate, py = pyridine) could be viewed as an 8-connected node or a dimer of 3-connected binuclear {LiZn(RCOO)3} carboxylate complexes. A solvothermal reaction of c with biphenyldicarboxylic acid (H2bpdc) results in two layered MOFs [{LiZn}2(bpdc)3(dma)4]·3DMA·H2O (1a ⊃ DMA) and [{LiZn}2(bpdc)3(nmp)4]·4NMP (1b ⊃ NMP) in dimethylacetamide (DMA) or N-methyl-2-pyrrolidone (NMP) solvents, respectively. The reaction of [Li2Zn2(piv)6(py)2] with H2bpdc and diazabicyclo[2.2.2]octane (dabco) in dimethylformamide (DMF) affords a 3D MOF [Li2Zn2(bpdc)3(dabco)]·9DMF·4H2O (2 ⊃ DMF) with an open structure. The frameworks in 1a and 1b are based on 3-connected binuclear nodes, connected through linear bpdc2− anions into a twofold interwoven honeycomb (hcb) layers, packed in ABAB manner. The tetranuclear units in 2 are connected by both bpdc2− and dabco into a 3D non-interpenetrated net with body-centered cubic (bcu) topology. The solvent molecules in both 1 and 2 could be substituted to various aromatic species, which nature affects the photoluminescence properties of the framework in a different way. For example, the substitution to nitrobenzene completely quenches the luminescence while the inclusion of benzyl alcohol, anisole, acetophenone into porous channels of 2 results in a marked shift of the emission peak maxima as well as an enhancement of the quantum yields.

Dynamic gamma-ray monitoring at radioprotection levels with extrinsic polymer optical fiber sensors

The dynamic performance of extrinsic gamma-ray sensors at radioprotection levels is studied. The sensors have been fabricated with chemically etched polymer optical fibers covered with an inorganic scintillator powder (Terbium doped Gadolinium Oxysulfide). This scintillator shows a maximum emission peak at 543 nm, therefore only the signal amplitude at this wavelength has been measured with a commercial grade CCD spectrometer. The transducers have been done at the end of both short (1 m) and large fiber patchcords (27 m). Short patchcords are further mechanically spliced to a fiber link 25 m length through an industrial grade connector-less mating sleeve, and therefore can be easily replaced if needed.All tests were run under gamma irradiation from a 137Cs source, the reference isotope for environmental protection. The measured response of the devices is very repeatable and stable, with a percentage standard deviation below 2% when the air kerma rate is above 1 Gy/h. This deviation increases for lower rates. A Limit of Detection of 0.2 Gy/h, with an integration time at the detection stage of 10 s, has been achieved for transducers done in the 1 m length patchcords spliced to the 25 m length fiber link. This integration time can be further reduced when no splice is included between transducer and detection unit. The behavior of the devices is linear with the delivered air kerma rate, and can provide reliable measurements under repeated radiation exposures. This behavior makes the sensors useful to quickly detect the presence of hazardous radioactive materials in accidental leakage scenarios.

Enhanced photoluminescence properties and energy transfer in a novel Eu3+ doped PbSmB7O13 red-emitting phosphor

A series of PbSm1-xB7O13:xEu3+ phosphors were synthesized by the high temperature solid-state reaction method. The phase composition, morphology, luminescent properties and energy transfer of as-prepared samples were characterized using X-ray power diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra (PL). The results show that the maximum emission peak excited under 400 nm was observed at about 614 nm owing to the 5D0 → 7F2 transition of Eu3+ ions. The intensity of the main emission line (5D0 → 7F2 transition of Eu3+) was effectively strengthened because of the energy transfer from Sm3+ to Eu3+ in the Sm3+ and Eu3+ co-doped system. The CIE chromaticity coordinates of PbSm0.2B7O13:0.8Eu3+ are calculated to be (0.6842, 0.3213), which correspond to red emission and are closer to the standard red color coordinates. This study indicates that PbSm1-xB7O13:xEu3+ phosphors could be efficiently excited by near-UV chips for potential application in W-LEDs.

Sensitive and selective detection of copper ions using low cost nitrogen doped carbon quantum dots as a fluorescent sensing plateform

The current study reports a facile, single step microwave assisted synthesis of nitrogen, oxygen-doped carbon quantum dots (NCQDs) with high quantum yield (~36%). The synthesized NCQDs with an average size of 4 nm demonstrate many fold increase in the intensity of photoluminescence (PL) over the undoped carbon quantum dots (CQDs). UV–Vis absorption peak exhibits a red shift of 26 nm for NCQDs with respect to pristine CQDs. The spectral shift was further confirmed by density functional theory based calculations. X-ray photoelectron spectroscopy measurements reveal the graphitic nature and significantly high nitrogen doping of NCQDs (38.2%). The NCQDs exhibited excitation dependent PL behaviour in the visible region with maximum emission peak recorded at 415 nm with optimum excitation wavelength of 340 nm. The remarkably enhanced PL properties of NCQDs have been employed as fluorescent probe for sensitive and selective sensing of Cu2+ ions. The Cu2+ quenches the fluorescence intensity of NCQDs due to its high binding affinity towards N and O containing functional groups in quantum dots. The NCQDs render a simple, reliable and sensitive detection of Cu2+ ions with limit of detection as low as 1.8 µM.

Investigation of environmental and concentration effects on fluorescence properties of AlQ3 using mesoporous silica and polyacrylate

In this work, for the first time, control over the position of maximum emission peak for fluorophore, using embedded tris(8-hydroxyquinoline) aluminum (AlQ3) complexes into different types of host materials, can be achieved. Moreover, the environmental and concentration effects on luminescent properties were studied. In this regard, different concentrations of AlQ3 were embedded into the poly(methyl methacrylate-co-butyl acrylate) (PMMA-co-PBuA) nanoparticles as organic host materials by emulsion polymerization. It is established that the dilution of AlQ3 in the polymer matrix leads to blue-shift of the luminescence maximum up to 0.32 eV compared to pure AlQ3. Moreover, AlQ3 was embedded in SBA-15 type mesoporous silica as an inorganic host material by physical adsorption. Finally, this functionalized mesoporous silica was incorporated into PMMA-co-PBuA transparent matrix by blending method to obtain Co-Poly-AlQ3-SBA-15 as organic–inorganic composite material. It was found that there is no significant wavelength shift on the maximum emission peak of the organic–inorganic composite at various concentrations of AlQ3-SBA-15. The prepared materials were characterized by powder X-ray diffraction (XRD), N2 adsorption–desorption, NMR, Fourier transform infrared (FT-IR), dynamic light scattering (DLS), scanning electron microscopy (SEM) and fluorescence spectra.

Green synthesis of white-light-emitting ZnSe:Eu2+, Mn2+ quantum dots in an aqueous solution

High-quality ZnSe:Eu, Mn quantum dots (QDs) with white light emitting were synthesized via a green preparation method in an aqueous solution using thioglycolic acid as a stabilizing agent. The composition of the QDs could be flexibly controlled by varying the amount of Eu or Mn cation. The effects of reflux time and Eu2+ ion dopant concentration on the luminescence properties were systematically investigated. The obtained QDs were characterized by photoluminescence spectrometry, X-ray powder diffraction, and high-resolution transmission electron microscopy. The proposed method formed cubic ZnSe:Mn2+, Eu2+ QDs with the maximum emission peak at 460 and 580 nm. In the optimal condition, the quantum yields of ZnSe:Mn2+, Eu2+ QDs could reach 27.68%. The CIE color coordinates were (0.328, 0.334), which agreed with those of pure white light (0.33, 0.33). The results verified that the ZnSe:Mn2+, Eu2+ QDs exhibited potential in light-emitting diode applications.

Polymer fluorescent probe for Hg(II) with thiophene, benzothiazole and quinoline groups

A facile polymer consisted of quinoline, thiophene and benzothiazole groups was designed and synthesized by Suzuki coupling reaction. The study of photophysical property indicated that the polymer was a red light emitter with maximum absorption (490nm) and emission (610nm) peaks. The assays of thermal gravimetric analysis (TGA) and cyclic voltammetry (CV) revealed that the polymer possesses good thermal (Td, 228°C) and electrochemical properties. The experimental data based on the cyclic voltammetry were in good agreement with the results of theoretical calculations. The sensing processes of the polymer to metal ions were investigated by UV–vis absorption and fluorescence emission spectra. The results showed that the polymer had high selectivity and sensitivity for Hg(II) ions with an obvious “turn-on” fluorescence in the presence of Hg(II). Noticeably, the polymer as a fluorescence probe can be applied in the detection in practical samples. The attribution of the work lies in providing a new strategy for design and application of polymer probes in analysis and testing fields.

New Tl2LaBr5: Ce3+ crystal scintillator for γ-rays detection

In this study we present our preliminary report on the scintillation properties of new Ce-doped Tl2LaBr5 single crystal. Two zones vertical Bridgman technique is used for the growth of this compound. Pure and Ce-doped samples showed maximum emission peaks at 435nm and 415nm, respectively. Best light yield of 43,000±4300ph/MeV with 6.3% (FWHM) energy resolution is obtained for 5% Ce-doped sample under γ-ray excitation. Single exponential decay time constant of 25ns is observed for 5% Ce doped sample. Effective Z-number is found to be 67, therefore efficient detection of X- and γ-ray will be possible. Preliminary results revealed that this compound will be an ideal candidate for the medical imaging techniques. Further investigations are under way for the determination of optimized conditions of this compound.

Effect of various red phosphorescent dopants in single emissive white phosphorescent organic light-emitting devices

In order to realize single emissive white phosphorescent organic light-emitting devices (PHOLEDs) with three color phosphorescent dopants (red, green, and blue), the energy transfer between the host material and the three dopants, as well as the among the three dopants themselves, should be considered and optimized. To explore the effect of red phosphorescent dopant on the color rendering index (CRI), the authors investigate the wavelength position of the maximum emission peak from three phosphorescent dopants. The CRI and luminous efficiency of white PHOLED in which Ir(pq)2(acac) acts as the red phosphorescent dopant are found to be greater than those of devices prepared using Ir(piq)3 and Ir(btp)2(acac) as the emission spectrum has a relatively high intensity near the human perception of blue, red, and green wavelengths. Furthermore, we demonstrate that the performance of the three dopants is related to the absorption characteristics of the red phosphorescent dopant. With a maximum emission peak at 600 nm, Ir(pq)2(acac) has a higher intensity in the concave section between 550 and 600 nm seen for red and blue dopants. In addition, the long metal-to-ligand charge transfer (MLCT) absorption tail of Ir(pq)2(acac) overlaps with the emission spectra of the green dopant, enhancing emission. Such energy transfer mechanisms are confirmed to optimize white emission in the single emissive white PHOLEDs.

In situ synthesis of NIR-light emitting carbon dots derived from spinach for bio-imaging applications.

Near infrared (NIR)-light emitting fluorescent probes have attracted extensive research attention in the bioimaging field due to their deep tissue penetration, minimal auto-fluorescence and lower emission light damage to bio-tissues. Herein, we designed and prepared NIR-light emitting CDs (R-CDs) from spinach by a one-step solvothermal method. The R-CDs exhibited good water solubility, a maximum fluorescence emission peak at 680 nm, a high quantum yield of 15.34%, remarkable photo-stability and resistance to metal ions in a body-simulating environment, excellent compatibility, negligible toxicity, and superior labelling capability in vitro and in vivo. These findings significantly highlight the design of NIR-light emitting CDs and exploit their bio-imaging applications.

Scheelite (CaWO4)-type microphosphors: Facile synthesis, structural characterization and photoluminescence properties

Scheelite (CaWO4)-type microphosphors were synthesized by the precipitation method assisted with cetyltrimethyl ammonium bromide (CTAB). All compounds crystallized in the tetragonal structure with space group [Formula: see text] (No. 88). FE-SEM micrographs illustrate the spherical-like morphologies and rough surface. PL spectra indicate the broad emission peak maximum at 613 nm under UV excitation. Luminescence decay curves monitored by [Formula: see text] transition ([Formula: see text] nm) of Eu[Formula: see text] in doped CaWO4 are presented, the curves exhibit a single-exponential feature and the lifetime for doped CaWO4 is 0.61 ms.