Showing papers on "Stokes shift published in 2019"
TL;DR: In this paper, a time-domain τ-dot was proposed to convert the NIR pulsed excitation into long-decaying luminescence with an efficiency approaching 100%.
Abstract: The optically transparent biological window in the near-infrared (NIR) spectral range allows deep-tissue excitation and the detection of fluorescence signals1,2. Spectrum-domain discrimination of NIR contrast agents via an upconversion or downshifting scheme requires sufficient (anti-) Stokes shift to separate excitation and fluorescence emission. Here, we report a time-domain (τ) scheme in which about 5,000 ytterbium signal transducers are condensed within an optically inert and biocompatible CaF2 shell (2.3 nm), which forms a 14.5 nm τ-dot. Because of the long-lived and spectrally narrowly defined excited state of pure ytterbium ions, the NIR τ-dot can convert the NIR pulsed excitation into long-decaying luminescence with an efficiency approaching 100%. Within a safe injection dosage of 13 μg g−1, an excitation power density of 1.1 mW cm−2 was sufficient to image organs with a signal-to-noise ratio of >9. The high brightness of τ-dots further allows long-term in vivo passive targeting and dynamic tracking in a tumour-bearing mouse model. By time-shifting short-pulse excitation photon energy into prolonged luminescent emission in the time domain, both the number of light signal transducers in sub-15 nm nanoparticles and the near-infrared-in to near-infrared-out conversion efficiency can be maximized, advancing in vivo optical bioimaging.
143 citations
TL;DR: In this article, the photoluminescence (PL) emission in double perovskite (Cs2AgBiBr6) is investigated and it is shown that the PL emission is related to a color center rather than a band-to-band transition.
Abstract: Double perovskite crystals such as Cs2AgBiBr6 are expected to overcome the limitation of classic hybrid organic–inorganic perovskite crystals related to the presence of lead and the lack of structural stability. Perovskites are ionic crystals in which the carriers are expected to strongly couple to lattice vibrations. In this work we demonstrate that the photoluminescence (PL) emission in Cs2AgBiBr6 is strongly influenced by the strong electron–phonon coupling. Combining photoluminescence excitation (PLE) and Raman spectroscopy we show that the PL emission is related to a color center rather than a band-to-band transition. The broadening and the Stokes shift of the PL emission from Cs2AgBiBr6 is well explained using a Franck–Condon model with a Huang–Rhys factor of S = 11.7 indicating a strong electron–phonon interaction in this material.
127 citations
TL;DR: The cyan-green phosphor Lu2BaAl4SiO12:Ce3+ enables to fabricate a superhigh color rendering w-LED ( Ra = 96.6), verifying its superiority and application prospect in high-quality solid-state lightings.
Abstract: High-quality white light-emitting diodes (w-LEDs) are mainly determined by conversion phosphors and the enhancement of cyan component that dominates the high color rendering index. New phosphors (Lu2M)(Al4Si)O12:Ce3+ (M = Mg, Ca, Sr and Ba), showing a cyan-green emission, have been achieved via the co-substitution of Lu3+-Al3+ by M2+-Si4+ pair in Lu3Al5O12:Ce3+ to compensate for the lack of cyan region and avoid using multiple phosphors. The excitation bands of (Lu2M)(Al4Si)O12:Ce3+ (M = Mg, Ca, Sr and Ba) show a red-shift from 434 to 445 nm which is attributed to the larger centroid shift and crystal field splitting. The enhanced structural rigidity associated with the accommodation of larger M2+ leads to a decreasing Stokes shift and the corresponding blue-shift (533 → 511 nm) in emission spectra, along with an improvement in thermal stability (keeping ∼93% at 150 °C). The cyan-green phosphor Lu2BaAl4SiO12:Ce3+ enables to fabricate a superhigh color rendering w-LED ( Ra = 96.6), verifying its superiority and application prospect in high-quality solid-state lightings.
119 citations
TL;DR: A strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals is reported, implying strongly anharmonic lattice dynamics.
Abstract: Lead-halide perovskites have emerged as promising materials for photovoltaic and optoelectronic applications. Their significantly anharmonic lattice motion, in contrast to conventional harmonic semiconductors, presents a conceptual challenge in understanding the genesis of their exceptional optoelectronic properties. Here we report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals. This behavior stands in stark contrast to that exhibited by more conventional crystalline semiconductors. We correlate the electronic spectra with the anti-Stokes and Stokes Raman vibrational spectra. Dielectric solvation theories, originally developed for excited molecules dissolved in polar liquids, reproduce our experimental observations. Our approach, which invokes a classical Debye-like relaxation process, captures the dielectric response originating from the incipient anharmonicity of the LO phonon at about 20 meV (160 cm−1) in the lead-bromide framework. We reconcile this liquid-like model incorporating thermally-activated dielectric solvation with more standard solid-state theories of the emission Stokes shift in crystalline semiconductors. Lead halide perovskites have unique electronic properties that depend on the crystal’s anharmonicity. Dielectric solvation theories, developed for molecules dissolved in polar liquids, are shown here to reproduce the temperature behavior of carrier solvation in the electronic spectra, implying strongly anharmonic lattice dynamics.
111 citations
TL;DR: These HBIE-CDs were successfully used for rapid, and especially wash-free subcellular in situ imaging of nucleus in living cells in a fluorescence turn on mode, which has a great practicability to be used for nucleus imaging in bioanalytical studies and clinical applications.
Abstract: Carbon dots (CDs) are emerging as powerful tools for biosensing and bioimaging because of their intrinsic properties such as abundant precursors, facile synthesis, high biocompatibility, low cost, and particularly robust tunability and stability. In this work, a new type of CDs was prepared from m-phenylenediamine and folic acid by hydrothermal method. Interestingly, the as-prepared CDs show blue emission in non-hydrogen-bonding solution, whereas robust green emission in hydrogen-bonding solution. Based on this phenomenon, a novel fluorescence sensing mechanism named as hydrogen-bonding-induced emission (HBIE) was proposed. The HBIE-CDs have large Stokes shift (141 nm) in water, good biocompatibility, and ultrasmall size, which facilitates their translocation into living cells. Very importantly, the as-prepared HBIE-CDs show strong affinity toward nucleic acid without interference from other biological species. After binding with DNA/RNA through hydrogen bond, as high as 6-fold green fluorescence enhancement of HBIE-CDs was observed. Since the nucleus is rich in DNA/RNA, these HBIE-CDs were successfully used for rapid and, especially, wash-free subcellular in situ imaging of the nucleus in living cells in a fluorescence turn on mode, which has a great practicability to be used for nucleus imaging in bioanalytical studies and clinical applications.
104 citations
TL;DR: Aqueous acid-based synthesis of lead-free tin halide perovskites with near-unity photoluminescence quantum efficiency and high chemical yield is described.
Abstract: Recently, lead halide perovskites with outstanding emission performance have become new candidate materials for light-emitting devices and displays; however, the toxicity of lead and instability of halide perovskites remain significant challenges. Herein, we report the aqueous acid-based synthesis of highly emissive two-dimensional (2D) tin halide perovskites, (octylammonium)2SnX4 (X = Br, I, or mixtures thereof), which displayed a high absolute photoluminescence (PL) quantum yield of near-unity in the solid-state, PL emission centered at 600 nm with a broad bandwidth (136 nm), a large Stokes shift (250 nm), long-lived luminescence (τ = 3.3 μs), and zero overlap between their absorption and emission spectra. Significantly, the stability study of 2D tin halide perovskites monitored by the PL quantum yield showed no changes after 240 days of storage at room temperature under ambient air and humidity conditions. The PL emission of the 2D tin halide perovskites was tuned from yellow to deep red by controlling halide composition. Furthermore, new yellow phosphors with superior optical properties are used to fabricate UV pumped white light emitting diodes (WLEDs). We expect these results to facilitate the development of new environmentally friendly and high-performance phosphors for future lighting and display technologies.
94 citations
TL;DR: The Y-CDs display low cytotoxicity and were successfully used to image Ag(I) and GSH in H1299 cells, and the mechanism of yellow fluorescent CDs for the detection of Ag+ and glutathione is presented.
Abstract: Yellow-emissive carbon dots (Y-CDs) were prepared by a solvothermal method using anhydrous citric acid and 2,3-phenazinediamine as the starting materials. The Y-CDs display a 24% fluorescence quantum yield, a 188-nm Stokes’ shift and excellent stability. They are shown here to be excellent fluorescent probes for the determination of Ag(I) ion and glutathione (GSH). If exposed to Ag(I) ions, they are bound by the carboxy groups of the Y-CDs, and this causes quenching of fluorescence (with excitation/emission maxima at 380/568 nm) via a static quenching mechanism. This effect was used to design a fluorometric assay for Ag(I). The quenched fluorescence of the Y-CDs can be restored by adding GSH due to the high affinity of GSH for Ag(I). The calibration plot for Ag(I) is linear in the 1–4 μM Ag(I) concentration range, and the limit of detection is 31 nM. The respective values for GSH are 5–32 μM, and 76 nM, respectively. The method was applied to the detection of Ag(I) in spiked environmental water samples and gave recoveries ranging from 93 to 107%. It was also applied to the determination of GSH in tomatoes and purple grapes and gave satisfactory recoveries. The Y-CDs display low cytotoxicity and were successfully used to image Ag(I) and GSH in H1299 cells.
93 citations
TL;DR: A π-extended double [7]carbohelicene 2 with fused pyrene units was synthesized, revealing remarkable chiral stability with a fairly high isomerization barrier of 46 kcal mol–1, according to density functional theory calculations, which allowed optical resolution by chiral HPLC and suggests potential applications in chiroptical devices.
Abstract: A π-extended double [7]carbohelicene 2 with fused pyrene units was synthesized, revealing considerable intra- and intermolecular π-π interactions as confirmed with X-ray crystallography. As compared to the previous double [7]carbohelicene 1, the π-extended homologue 2 demonstrated considerably red-shifted absorption with an onset at 645 nm (1: 550 nm) corresponding to a smaller optical gap of 1.90 eV (1: 2.25 eV). A broad near-infrared emission from 600 to 900 nm with a large Stokes shift of ∼100 nm (2.3 × 103 cm-1) was recorded for 2, implying formation of an intramolecular excimer upon excitation, which was corroborated with femtosecond transient absorption spectroscopy. Moreover, 2 revealed remarkable chiral stability with a fairly high isomerization barrier of 46 kcal mol-1, according to density functional theory calculations, which allowed optical resolution by chiral HPLC and suggests potential applications in chiroptical devices.
89 citations
TL;DR: A new reaction-based red to near-infrared (NIR) fluorescent turn-on probe for H2S that shows high selectivity and sensitivity for H 2S without interference from biothiols is developed.
85 citations
TL;DR: Analysis of combined in situ high-pressure photolu-minescence, absorption, and angle-dispersive X-ray diffraction data indicates that the observed PIE can be attributed to the emission from self-trapped excitons.
Abstract: Two-dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure-property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure-induced emission (PIE) at 2.5 GPa with a broad emission band and large Stokes shift from initially nonfluorescent (BA)4 AgBiBr8 (BA=CH3 (CH2 )3 NH3 + ). The emission intensity increased significantly upon further compression up to 8.2 GPa. Moreover, the band gap narrowed from the starting 2.61 eV to 2.19 eV at 25.0 GPa accompanied by a color change from light yellow to dark yellow. Analysis of combined in situ high-pressure photoluminescence, absorption, and angle-dispersive X-ray diffraction data indicates that the observed PIE can be attributed to the emission from self-trapped excitons. This coincides with [AgBr6 ]5- and [BiBr6 ]3- inter-octahedral tilting which cause a structural phase transition. High-pressure study on (BA)4 AgBiBr8 sheds light on the relationship between the structure and optical properties that may improve the material's potential applications in the fields of pressure sensing, information storage and trademark security.
84 citations
TL;DR: The mechanism constructed here offers a new route for tuning the optical properties of 2D perovskites, and Sequential amorphization of the organic and inorganic layer is confirmed by high pressure Raman and X‐ray diffraction measurements, suggesting the particularity of layered crystal structures.
Abstract: 2D Ruddlesden-Popper halide perovskites, which incorporate hydrophobic organic interlayers to considerably improve environmental stability and optical properties diversity, have attracted substantial research attention for optoelectronic applications. The burgeoning broad emission arising from exciton self-trapping of 2D perovskites shows a strong dependence on a deformable structure. Here, the pressure-induced broadband emission of layered (001) Pb-Br perovskite with a large Stokes shift in the visible region is observed by finely improving lattice distortion to increase exciton-phonon coupling under hydrostatic pressure. Band gap narrows ≈0.5 eV under modest pressure, mainly due to the large compressibility of the orientational organic layer, confirming that the bulky organic cations notably influence the structure and, in turn, the various properties of materials. Sequential amorphization of the organic and inorganic layer is confirmed by high pressure Raman and X-ray diffraction measurements, suggesting the particularity of layered crystal structures. The mechanism constructed here offers a new route for tuning the optical properties of 2D perovskites.
TL;DR: The low threshold excitation intensity provided by the present system offers promising potential for application in terrestrial solar energy conversion.
Abstract: A series of Pt(II)-Schiff base complexes were synthesized as triplet sensitizers for the purpose of tuning the singlet and triplet energy levels so as to minimize energy loss during triplet-triplet annihilation (TTA) upconversion (UC). A deep-red to blue TTA-UC was achieved with an unprecedentedly large anti-Stokes shift of 1.08 eV. UC quantum yields of up to 21% (with a theoretical maximum efficiency of 50%) were observed in solution. The complexes also showed efficient UC emission in air-saturated hydrogels with a UC quantum yield up to 14.8%, which is much higher than the highest previously reported value. The low threshold excitation intensity provided by the present system offers promising potential for application in terrestrial solar energy conversion.
TL;DR: MZC-AC displays highly sensitive and selective response to Cys over homocysteine (Hcy) and glutathione (GSH) and could be used to detect Cys in living cells.
TL;DR: The quantitative determination of environmental water systems and the visualization fluorescence of D DPB test strips provides a strong evidence for the applications of DDPB.
TL;DR: It is depicted that a simple modification of substituents on the mercaptoimidazole ligand dictates the self-assembly and photophysical properties of the clusters.
TL;DR: Excitation into the spin-allowed S0 → 1CT absorption band of a spin-orbit charge transfer intersystem crossing (SOCT-ISC) triplet photosensitizer was used as a new strategy to increase the anti-Stokes shift in triplet-triplet annihilation (TTA) upconversion.
TL;DR: In this article, a new AIE-based fluorescent probe (MTPA-Cy) was synthesized via condensation reaction of 3-ethyl-1,1,2-trimethyl- 1H-indolium iodide with 4-(bis(4-methoxyphenyl)amino)benzaldehyde, in which indole quaternary salt was incorporated as the mitochondria-target and 4-bis( 4-methyl-amino)-benzene (TPA) was the AIEactive fluorescent reporter.
Abstract: We report here a brand new AIE based fluorescent probe (MTPA-Cy) for monitoring the level of ClO−. MTPA-Cy was synthesized via condensation reaction of 3-ethyl-1,1,2-trimethyl-1H-indolium iodide with 4-(bis(4-methoxyphenyl)amino)benzaldehyde, in which indole quaternary salt was incorporated as the mitochondria-target and 4-(bis(4-methoxyphenyl)amino)benzene (TPA) the AIE-active fluorescent reporter. Oxidation by ClO− of the ethylene bridge between TPA unit and indole quaternary salt moiety triggered substantial absorption and fluorescence changes. Upon introduction of ClO−, absorption of MTPA-Cy at 538 nm declined while a new absorption at shorter wavelength around 365 nm developed, manifested by an obvious color change from red to colorless, and fluorescence at 514 nm increased by 16.3-fold under excitation of 365 nm which means a large Stokes shift of ca. 150 nm. A LOD of 13.2 nM was calculated for ClO− in aqueous buffer solution, allowing thereby for detection of ClO− in a wide variety of biological systems. The oxidation product also exhibits two-photon excitation performance since its fluorescence was observed under excitation by an NIR light of 730 nm. MTPA-Cy was applied for detection of ClO− in solution, aggregated forms, solid state and living cells.
TL;DR: In this article, a zircon-type ScVxP1−xO4:Bi3+ (0 ≤ x ≤ 1) emission-tunable solid solution that has a strong UV excitation intensity yet no significant light absorption is presented.
Abstract: Unlike rare earth (RE) (e.g., Eu2+) and non-RE (e.g., Mn2+) doped tunable solid solutions that frequently suffer from the visible re-absorption issue, the Bi3+ ion features the remarkable advantages of a strong UV excitation intensity and an excitation tail of less than 430 nm, giving Bi3+ a strong potential to solve the re-absorption issue for future lighting technology. Herein, we report a type of zircon-type ScVxP1−xO4:Bi3+ (0 ≤ x ≤ 1) emission-tunable solid solution that has a strong UV excitation intensity yet no significant light absorption. We reveal that gradual substitution of larger V ions for smaller P ions, which means expansion of the lattice cell, can shift the excitation edge from 295 to 385 nm, the excitation tail from 340 to 425 nm and emission position from 455 to 641 nm, without causing a large change to the Stokes shift. This spectral shifting is found to be a consequence of the complex dependence of the intra-ion and charge-transfer related transitions of Bi3+ with the crystal structure. Owing to the remarkable excitation-triggered multi-emission properties, we then discover that the ScVxP1−xO4:Bi3+ solid solution can serve as a type of potential material for anti-counterfeiting and information protection applications. This work can provide design insights into discovering more RE and non-RE doped tunable solid solutions in the future, through modulation of the secondary cations in the isostructural crystals.
TL;DR: In this paper, the defect chemistry and physics of Cs4PbBr6 were explored using first-principles theory and self-consistent Fermi level analysis.
Abstract: Cs4PbBr6 is a member of the extended halide perovskite family that is built from isolated (zero-dimensional) PbBr64− octahedra with Cs+ counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310–375 nm) with efficient luminescence in the green region (∼540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs4PbBr6. We find a heavily compensated system where the room-temperature carrier concentrations (<109 cm−3) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br3) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission.
TL;DR: In this paper, the effect of chemical composition and structure on Stokes shift, an important luminescence property, has not been studied systematically; however, the authors provide a feasibility to predict the emission spectrum of Ce3+/Eu2+ doped inorganic compounds and discover the suitable host lattice for required phosphors.
TL;DR: The results indicate that this NIR fluorescent probe can be used as a new practical tool for imaging of endogenous CO in living systems with high selectivity, high sensitivity and a low detection limit.
TL;DR: In this article, the authors showed that chemically active metal ns2 lone pairs play an important role in exciton relaxation and dissociation in low-dimensional halide perovskites.
Abstract: Based on first-principles calculations, we show that chemically active metal ns2 lone pairs play an important role in exciton relaxation and dissociation in low-dimensional halide perovskites. We studied excited-state properties of several recently discovered luminescent all-inorganic and hybrid organic-inorganic zero-dimensional (0D) Sn and Pb halides. The results show that, despite the similarity in ground-state electronic structure between Sn and Pb halide perovskites, the chemically more active Sn2+ lone pair leads to stronger excited-state structural distortion and larger Stokes shift in Sn halides. The enhanced Stokes shift hinders excitation energy transport, which reduces energy loss to defects and increases the photoluminescence quantum efficiency (PLQE). The presence of the ns2 metal cations in the 0D halide perovskites also promotes the exciton dissociation into electron and hole polarons especially in all-inorganic compounds, in which the coupling between metal-halide clusters is significant.
TL;DR: In this article, a novel near-infrared and two-photon ratiometric fluorescent probe NIR-SO2-TP was first proposed for optical SO2 sensing, which is based on coumarin-benzopyrylium π-conjugated platform, exhibited high selectivity, rapid response time, lower detection limit and a large Stokes shift.
Abstract: As a critical gaseous signaling molecule, SO2 is involved in multiple physiological and pathological processes. However, the pathogenesis of many serious diseases including lung cancer, cardiovascular diseases and neurological disorders caused by excessive inhalation of SO2 is still unknown. Hence, the development of reliable analytical methods for efficiently and specifically monitoring SO2 in living systems is of significance. In this work, a novel near-infrared and two-photon ratiometric fluorescent probe NIR-SO2-TP was first proposed for optical SO2 sensing. The newly synthesized fluorescent probe NIR-SO2-TP, which is based on coumarin-benzopyrylium π-conjugated platform, exhibited high selectivity, rapid response time, lower detection limit and a large Stokes shift (185 nm). Importantly, the novel probe has been successfully applied to sense SO2 in living cells, tissues, zebrafish and living mice at both near-infrared and two-photon modes.
TL;DR: The in vitro imaging results indicated that the probe BT-1 was membrane-permeable and could be applied into the recognition of Cu2+ ions in living cells.
TL;DR: A new fluorescent probe, BMQA, obtained from the reaction of 2-(2-hydroxyphenyl) benzothiazole, methylquinoline, and acryloyl chloride is reported, which is possible to quantitatively detect cysteine (Cys) in 1% acetonitrile-containing PBS buffer solution (pH 7.2).
Abstract: Water solubility, large Stokes-shift, and near-infrared emission are essential properties required for a fluorescent probe used for intracellular detection of the analytes. Herein, we report a new fluorescent probe, BMQA, obtained from the reaction of 2-(2-hydroxyphenyl) benzothiazole, methylquinoline, and acryloyl chloride. By using this probe, it is possible to quantitatively detect cysteine (Cys) in 1% acetonitrile-containing PBS buffer solution (pH 7.2). The experimental results showed that the probe exhibited an excellent spectral performance with an emission wavelength at 740 nm, Stokes shift of 310 nm, and detection limit of 0.062 μM for Cys. Theoretical calculations were also conducted to clarify the luminescence mechanism of the system. In addition, the experiments performed on A549 living cells showed that BMQA is suitable for the in detection of Cys in human serum by fluorescence imaging.
TL;DR: In this paper, a new near-infrared (NIR) fluorescent probe was developed for the detection of CO in living systems, which is based on a unique cyanine fluorophore and uses an allyl ether moiety as the reaction site.
Abstract: A new near-infrared (NIR) fluorescent probe was developed for the detection of CO in living systems. This probe is based on a unique cyanine fluorophore and uses an allyl ether moiety as the reaction site. Optical studies in solution show that this probe has good water solubility and possesses desirable sensing properties for CO including rapid response, high selectivity and sensitivity, large Stokes shift (123 nm), distinct colorimetric changes, and significant turn-on NIR fluorescence changes at 715 nm with high signal-to-noise ratio. Ratiometric fluorescent detection of CO with this probe at 715 and 570 nm is also applicable. The sensing mechanism was proven to be a process of recovery of the fluorophore by removing the allyl group via Tsuji-Trost reaction. Furthermore, this probe was applied for detecting CO in living cells and animals with good bioimaging performance. Moreover, indicated by this probe, more CO could be produced under oxidative stress conditions. All the results indicate that this probe can be applied as a promising new tool for in vitro and in vivo detection of CO.
TL;DR: Fluorescence Stokes shift and specific fluorescence intensity (SFI) are proposed as novel indicators of hydrophobicity and MW that originate from the energy gap and photon efficiency of the fluorescence process, and can be readily extracted from a fluorescence excitation-emission matrix (EEM).
Abstract: Hydrophobicity and molecular weight (MW) are two fundamental properties of dissolved organic matter (DOM) in wastewater treatment systems. This study proposes fluorescence Stokes shift and specific fluorescence intensity (SFI) as novel indicators of hydrophobicity and MW. These indicators originate from the energy gap and photon efficiency of the fluorescence process and can be readily extracted from a fluorescence excitation-emission matrix (EEM). The statistical linkages between these indicators and hydrophobicity/MW were explored through investigation of DOM across 10 full-scale membrane bioreactors treating municipal wastewater. Stokes shift was found to exhibit a general rule among the hydrophobicity components in the order of hydrophilic substances (HIS) 100 kDa), SFI was found to be the most sensitive to the change of MW of 0.9). Hydrophobicity-related π conjugation and MW-dependent light exposure might be responsible for the correlations. These fluorescence indicators may be useful for convenient monitoring of DOM in wastewater treatment systems.
TL;DR: A new near-infrared (NIR) fluorescent turn-on probe (CDCI-CO) based on a novel coumarin-dicyanoisophorone hybrid fluorophore for detection of CO both in vitro and in vivo was reported and can be used as a promising new tool for studying CO in living systems.
TL;DR: In this paper, a semi-aromatic polyimide (DBrBP-PI) was newly synthesized using a biphenyltetracarboxylic dianhydride substituted with two bromine (Br) atoms.
Abstract: Colorless, transparent, and environmentally stable polymer films with large luminescence Stokes shift are in demand for down-conversion of solar UV radiation. To develop such a polymer film that exhibits phosphorescence at room-temperature with a large Stokes shift and excellent thermal stability, a semi-aromatic polyimide (DBrBP-PI) was newly synthesized using a biphenyltetracarboxylic dianhydride substituted with two bromine (Br) atoms. Thin films of DBrBP-PI were completely colorless because of effective suppression of the aggregation of the PI chains due to the steric effects of the Br-substituted dianhydride structure. The PI films exhibited bright green phosphorescence at 512 nm (Φ = 0.02) with a very large Stokes shift of 12 215 cm−1 as well as prompt blue fluorescence at around 408 nm when excited at 315 nm at 298 K. The glass transition and the 5 wt% loss temperatures of DBrBP-PI were 325 °C and 427 °C, respectively. The phosphoresce intensity of the DBrBP-PI film was significantly enhanced under vacuum (Φ = 0.22) and at low temperatures (Φ = 0.76 at 77 K) owing to suppression of triplet state quenching by atmospheric oxygen and dumping of the molecular motions of the PI chains in the solid film. The suggested material design concept shows a way towards creation of stable and efficient down-converters for UV radiation.
TL;DR: In this article, the external Stokes shift of lead halide perovskite nanocrystals (NCs) was found to be strongly dependent on photon recycling and photon reuse.
Abstract: Lead halide perovskite nanocrystals (NCs) have rapidly emerged as promising materials for low-cost and high-efficiency photovoltaic, optoelectronic, and photonic devices. The Stokes shift is a crucial parameter affecting their performance. In this work, we find that the external Stokes shift is strongly dependent on photon recycling. Due to the nonlinear nature of the quantum confinement effect (QCE), the bandgap distribution becomes extremely broad when the sizes are ultra-small, resulting in many repetitions of photon recycling and substantial emission redshift. Thereby, the smaller NCs exhibit larger external Stokes shifts. In detail, for the small NCs with the most probable size of 6.4 nm, the intrinsic Stokes shift is about 71 meV, but the observed external Stokes shift becomes 143.4 meV in the concentrated solution, whereas the intrinsic and apparent Stokes shifts are 69 and 97.6 meV for large NCs of 9.7 nm. Therefore, photon recycling significantly contributes to the external Stokes shift of perovskite NCs, in particular for the ultra-small sizes with strong QCE. This finding will add to the growing fundamental physical understanding of perovskites, which is of great interest due to their applications in photovoltaics and other fields.