Time-resolved observations have been made of the formation of vibrationally excited NO X 2 Π ( v ′) following collisional quenching of NO A 2 Σ + ( v = 0) by NO X 2 Π ( v = 0). Two time scales are ...observed, namely a fast production rate consistent with direct formation from the quenching of the electronically excited NO A state, together with a slow component, the magnitude and rate of formation of which depend upon NO pressure. A reservoir state formed by quenching of NO A 2 Σ + ( v = 0) is invoked to explain the observations, and the available evidence points to this state being the first electronically excited state of NO, a 4 Π. The rate constant for quenching of the a 4 Π state to levels v ′ = 11–16 by NO is measured as (8.80 ± 1.1) × 10 −11 cm 3 molecule −1 s −1 at 298 K where the error quoted is two standard deviations, and from measurements of the increased formation of high vibrational levels of NO(X) by the slow process we estimate a lower limit for the fraction of self-quenching collisions of NO A 2 Σ + ( v = 0) which lead to NO a 4 Π as 19%.
Carbon dots (CDs) possess unique optical properties such as tunable photoluminescence (PL) and excitation dependent multicolor emission. The quenching and recovery of the fluorescence of CDs can be ...utilized for detecting analytes. The PL mechanisms of CDs have been discussed in previous articles, but the quenching mechanisms of CDs have not been summarized so far. Quenching mechanisms include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). Following an introduction, the review (with 88 refs.) first summarizes the various kinds of quenching mechanisms of CDs (including static quenching, dynamic quenching, FRET, PET and IFE), the principles of these quenching mechanisms, and the methods of distinguishing these quenching mechanisms. This is followed by an overview on applications of the various quenching mechanisms in detection and imaging.
Graphical abstract
Schematic representation of the quenching mechanisms of carbon dots (CDs) which include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer(PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). All these effects can be used to detect and image analytes.
It is widely recognized that nonradiative quenching of excitons by other excitons and polarons become the dominant decay mechanism of these excitons at high excitation densities. These quenching ...processes cause the roll‐off in the efficiency of organic light‐emitting devices (OLEDs) and prevent lasing at high injection current densities. This review presents the optically‐detected magnetic resonance (ODMR) evidence for these photoluminescence‐ and electroluminescence‐quenching processes. And while it provides such evidence for quenching of singlet excitons by polarons and triplet excitons, it reveals the central role of the strongly spin‐dependent annihilation of triplet excitons by polarons, since under normal excitation conditions the steady‐state polaron and triplet exciton populations are 100–104 times the singlet exciton population. In addition, it also suggests that quenching of singlet excitons by bipolarons, likely stabilized by a counterpolaron or countercharge at specific sites, may also be a significant quenching mechanism that also affects the charge transport properties.
It is widely recognized that nonradiative quenching of excitons by other excitons and polarons become the dominant decay mechanism of these excitons at high excitation densities. These quenching processes cause the roll‐off in the efficiency of organic light‐emitting devices (OLEDs) and prevent lasing at high injection current densities. This review presents the optically‐detected magnetic resonance (ODMR) evidence for these photoluminescence‐ and electroluminescence‐quenching processes.
Understanding “efficiency roll‐off” (i.e., the drop in emission efficiency with increasing current) is critical if efficient and bright emissive technologies are to be rationally designed. Emerging ...light‐emitting electrochemical cells (LECs) can be cost‐ and energy‐efficiently fabricated by ambient‐air printing by virtue of the in situ formation of a p‐n junction doping structure. However, this in situ doping transformation renders a meaningful efficiency analysis challenging. Herein, a method for separation and quantification of major LEC loss factors, notably the outcoupling efficiency and exciton quenching, is presented. Specifically, the position of the emissive p‐n junction in common singlet‐exciton emitting LECs is measured to shift markedly with increasing current, and the influence of this shift on the outcoupling efficiency is quantified. It is further verified that the LEC‐characteristic high electrochemical‐doping concentration renders singlet‐polaron quenching (SPQ) significant already at low drive current density, but also that SPQ increases super‐linearly with increasing current, because of increasing polaron density in the p‐n junction region. This results in that SPQ dominates singlet‐singlet quenching for relevant current densities, and significantly contributes to the efficiency roll‐off. This method for deciphering the LEC efficiency roll‐off can contribute to a rational realization of all‐printed LEC devices that are efficient at highluminance.
The dynamic doping operation of light‐emitting electrochemical cells (LECs) renders the understanding of the efficiency roll‐off challenging. Herein, a method for quantification of major LEC loss factors, notably the outcoupling efficiency and exciton quenching, is presented. It reveals that singlet‐polaron quenching strongly affects the efficiency roll‐off in singlet‐emitting LECs because of increasing polaron concentration in the p‐n junction with increasing current .
A quenched and tempered steel for a large bearing ring was investigated. The heat treatment experiments were designed by using the L9 (34) type orthogonal form. Based on these conditions, a better ...combination of mechanical properties was obtained. The results showed that the quenching and the tempering temperatures were the most influential factors on the strength and toughness. The dislocation strengthening and the solid solution strengthening of the dissolved alloying carbides are the main mechanisms of increasing the strength by decreasing the tempering temperature and increasing the quenching temperature, respectively. The stripped carbides and long chain carbides strongly influence the differences in the tensile strength of the steels under different processes. The toughness AKv at −20°C was increased by 42.2J when the quenching temperature increased from 800 to 900°C. The stripped undissolved carbides at lower quenching temperature promoted crack propagation and cleavage fracture and thus decreased the toughness of the steel. The AKv was increased by 47.4J when the tempering temperature increased from 550 to 650°C. The long chain carbides distributed along the grain boundary and the martensitic laths with a high density of dislocations at the lower tempering temperature decreased the toughness. Oil quenching can improve both the strength and toughness by refining the martensitic microstructure.
As an important bioactive component in plants, chlorogenic acid (CGA) has been widely studied for its potential role in human health. In this work, cyan fluorescent silicon quantum dots were ...successfully synthesized via a simple one-pot method for the rapid detection of CGA. The optimal excitation and emission wavelength of the obtained SiQDs was 350 nm and 470 nm, respectively. When the CGA was added, the maximum emission intensity of the SiQDs can be effectively quenched due to dynamic and static mixed quenching mechanisms. More significantly, there was a remarkable linear correlation between fluorescence quenching efficiency and a broad concentration of CGA solution range from 10 to 150 μmol/L with a limit of detection (LOD) of 0.43 μmol/L. Furthermore, the proposed SiQDs were successfully applied to analyze CGA in coffee beans and instant coffee after simple pretreatment with satisfactory results. Based on these, a high sensitivity and excellent selectivity fluorescent probe detection system was constructed, and it provides a valuable platform for the detection of CGA and has broad application prospects in the biological and pharmaceutical analysis field.
•In this experiment, a novel silicon doped fluorescent quantum dots were successfully synthesized by one-pot hydrothermal method using 3-Aminopropyl triethoxysilane (APTES) as the silicon source.•Chlorogenic acid (CGA) is a kind of dietary phenolic compounds and has been widely studied for its potential role in human health.•The optimal emission intensity of the SiQDs can be effectively quenched by CGA due to the synergistic way of DQE (dynamic quenching) and SQE (static quenching).•The practical applications of SiQDs for the assay of CGA was successfully demonstrated in coffee with satisfactory recoveries.
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•Carbon dots are first synthesized by one-pot method with malonic acid and urea.•The carbon dots possess small size, favorable optical properties, and good stability.•The fluorescence ...of carbon dots can be selectively quenched by picric acid in 10s.•The strategy improves the sensitivity for detection of picric acid down to 51nM.
In this work, novel water-soluble and blue fluorescent carbon dots (C-dots) were synthesized using one-pot hydrothermal method with malonic acid and urea, and were then used as a label-free fluorescent probe for selective, sensitive, and rapid determination of picric acid (PA). The sizes of the as-prepared C-dots were mainly distributed in the range of 1.5–3.0nm with an average diameter of 2.5nm. Moreover, the C-dots displayed blue fluorescence with an emission peak at 395nm (320nm excitation), which also showed good stability and anti-photobleaching ability. Interestingly, the fluorescence of C-dots could be selectively quenched by PA within 10s. Based on this phenomenon, a label-free fluorescence assay was proposed for specific determination of PA. The fluorescence intensity of probe showed a linear response to PA in the concentration range of 0.1 to 26.5μM with a low detection limit of 51nM (S/N=3). Finally, the resultant fluorescent probe was successfully applied to the detection of PA in real water samples.
Step quenching and tempering (SQT) treatment was applied on HSLA steels to achieve a multi-phase microstructure with a superior deformation performance. Intercritical quenching and tempering (IQT) as ...well as direct quenching and tempering (DQT) were also processed for comparison. Moreover, effects of intercritical temperatures before quench for different treatment methods on microstructure evolution and mechanical property were also investigated. Compared with IQT and DQT, SQT treatment produces a fine microstructure composited of soft ferrite/pearlite and hard martensite, with precipitates distributed along boundaries to maintain a large quantity of dislocations on deformation. Experiments involving tension and impact tests show that SQT samples with such multi-phase microstructure exhibit a desirable combination of mechanical properties. With increasing the intercritical temperature, the phase fraction of martensite is increased, which improves the strength but weakens the impact toughness in regardless of heat treatment type. Meanwhile, the yield ratio (YR) is found to be increased by higher intercritical temperature in all samples, due to the larger phase fraction of martensite with a large dislocation density and a finer grain structure. Such scenario is elucidated by using a model proposed through Swift's equation. That indicates that the content of multi-phase microstructure can be efficiently controlled via adjusting the intercritical temperature using SQT, which enables the optimization of phase composition according to the requirements of actual productions in engineering.
Phosphor‐converted light‐emitting diode (pc‐LED) has drawn much interest due to the efficient light in solid‐state lighting, backlight display, security, and electronic devices. Thermal quenching ...(TQ) induced by nonradiative relaxation is one of the vital challenges that limits the widespread use of phosphors. Much efforts are devoted to designing different approaches to solve the emission loss at increasing temperature. Here, the mechanism of TQ and recent advances of anti‐TQ‐phosphor‐involved 5d–4f, 4f–4f, 6p–6s, 3d–3d transitions are discussed. Several important design strategies for anti‐TQ phosphors are summarized as follows: 1) defect engineering; 2) energy transfer; 3) structural modulation; 4) enhancing crystallinity; 5) layer structural design; 6) negative/zero thermal expansion; 7) surface coating and glass technology. Additionally, some future challenges and opportunities in this field are proposed. This review promotes the discovery of novel anti‐TQ phosphor materials for LED applications.
Recent advances for anti‐thermal‐quenching (anti‐TQ) phosphor materials in light‐emitting diode (LED) applications are based on design strategies: defect engineering, energy transfer, structural modulations, enhancing crystallinity, layer structural design, negative/zero thermal expansion, and surface coating strategy. These strategies contribute to the development and discovery of new anti‐TQ luminescent materials for high performance phosphor‐converted‐LED devices.
Luminescence quenching is a process exploited in transversal applications in science and technology and it has been studied for a long time. The luminescence quenching mechanisms are typically ...distinguished in dynamic (collisional) and static, which can require different quantitative treatments. This is particularly important - and finds broad and interdisciplinary application - when the static quenching is caused by the formation of an adduct between the luminophore - at the ground state - and the quencher. Due to its nature, this case should be treated starting from the well-known law of mass action although, in specific conditions, general equations can be conveniently reduced to simpler ones. A proper application of simplified equations, though, can be tricky, with frequent oversimplifications taking to severe errors in the interpretation of the photophysical data. This tutorial review aims to (i) identify the precise working conditions for the application of the simplified equations of static quenching and to (ii) provide general equations for broadest versatility and applicability. The latter equations can be used even beyond the sole case of pure quenching,
i.e.
, in the cases of partial quenching and even luminescence turn-on. Finally, we illustrate different applications of the equations
via
a critical discussion of examples in the field of sensing, supramolecular chemistry and nanotechnology.
Treatment of luminescence quenching upon adduct formation is often overlooked, leading to macroscopic errors. Here we provide a complete guide to its treatment, for correct mechanism assessment and to obtain reliable association constants.
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