Enhancement Of Emission Intensity Research Articles

Singlet Oxygen Flux, Associated Lipid Photooxidation, and Membrane Expansion Dynamics Visualized on Giant Unilamellar Vesicles.

The physical properties of lipid membranes depend on their lipid composition. Photosensitized singlet oxygen (1O2) provides a handle to spatiotemporally control the generation of lipid hydroperoxides via the ene reaction, enabling fundamental studies on membrane dynamics in response to chemical composition changes. Critical to relating the physical properties of the lipid membrane to hydroperoxide formation is the availability of a sensitive reporter to quantify the arrival of 1O2. Here, we show that a fluorogenic α-tocopherol analogue, H4BPMHC, undergoes a >360-fold emission intensity enhancement in liposomes following a reaction with 1O2. Rapid quenching of 1O2 by the probe (kq = 4.9 × 108 M-1 s-1) ensures zero-order kinetics of probe consumption. The remarkable intensity enhancement of H4BPMHC upon 1O2 trapping, its linear temporal behavior, and its protective role in outcompeting membrane damage provide a sensitive and reliable method to quantify the 1O2 flux on lipid membranes. Armed with this probe, fluorescence microscopy studies were devised to enable (i) monitoring the flux of photosensitized 1O2 into giant unilamellar vesicles (GUVs), (ii) establishing the onset of the ene reaction with the double bonds of monounsaturated lipids, and (iii) visualizing the ensuing collective membrane expansion dynamics associated with molecular changes in the lipid structure upon hydroperoxide formation. A correlation was observed between the time for antioxidant H4BPMHC consumption by 1O2 and the onset of membrane fluctuations and surface expansion. Together, our imaging studies with H4BPMHC in GUVs provide a methodology to explore the intimate relationship between photosensitizer activity, chemical insult, membrane morphology, and its collective dynamics.

Tunable Luminescence on Indium Halide Hybrid Regulated by Sb3+ Doping Concentration

AbstractSb3+ doping strategy has proved to be an effective way to regulate the band gap and improve the photophysical properties of metal halides. Herein, Sb3+‐doped lead‐free indium halide hybrid InCl6(C4H12N2)2Cl·H2O:xSb3+ (0 ≤ x ≤ 1) is reported. Upon Sb3+‐doping, the weak emission of InCl6(C4H12N2)2Cl experiences a significant enhancement in emission intensity with near‐unity photoluminescence quantum yield (PLQY). The photophysical data fitted by the power‐law equation verifies self‐trapped exciton emission for the broadband emission. Interestingly, the emission experiences a gradual red‐shift with emission color changing from green to yellow and finally to orange as the Sb3+‐doped concentration increases. The single crystal X‐ray diffraction, excitation wavelengths‐dependent emission spectra, and the distortion degree calculation of InCl6(C4H12N2)2Cl·H2O:xSb3+ (0 ≤ x ≤ 1) indicate that the Sb3+ concentration dependent luminescence results from the synergistic effect of crystal phase transition, change of luminescence center, and the distortion of crystal structure. This achievement represents a successful strategy to achieve the photophysical properties modulation of metal halides for versatile optical applications.

Ternary electrofluorochromic behavior of the terpyridine Eu(III) complex with a Bis-Arylamine redox group

The terpyridine Eu(III) complex with an alkyl-substituted phenyl-capped aniline dimer shows ternary electrofluorochromic behavior under different potentials. • Terpyridine Eu(III) complexes with multiple redox states. • The resulted complex displays an unique electrofluorochromic behavior. • With ternary conversion among orange, dark-blue and pale-yellow colors. • And red, deep-blue and greenish-blue PL emissions. Three new terpyridine Eu(III) complexes, [( L 1-3 )Eu(HFA) 3 ] (where L 1 = 4’-phenyl-2,2’:6’,2’’-terpyridine, L 2 = 4’-{[ p -(N-butyl-N-phenyl)amino]-phenyl}-2,2’:6’,2’’-terpyridine}, L 3 = 4’-{ p -[ p -(N,N′-dibutyl-N′-phenyl)-phenyldiamino]-phenyl}-2,2’:6’,2’’-terpyridine, and HFA = hexafluoroacetylacetone), have been successfully synthesized and characterized by UV-vis absorption spectrum, FTIR, MALDI-TOF MS and elemental analysis. The X-ray crystallography of complex [( L 2 )Eu(HFA) 3 ] shows that the europium(III) ion is nine-coordinated with N3O6 donors in normal ranges. Owing to the antenna effect, complex [( L 1 )Eu(HFA) 3 ] ( Ф = 0.44) possesses ca . 3 times enhancement of the metal-centered red emission intensity compared to that of precursor Eu(HFA) 3 ( Ф = 0.16). The most interesting is that complex [( L 3 )Eu(HFA) 3 ] displays an unique electrofluorochromic behavior with the ternary absorption (orange/dark-blue/pale-yellow) and PL emission (red/deep-blue/greenish-blue) conversions, in which the ICT, cation radicals-related and Eu(III)-centered electronic transitions are involved.

Naked-Eye Optical Recognition of Ammonia Vapor and Melamine in Water Using a Fluorophore Appended Polymer Matrix.

The generation of solid-state emitters is a challenge due to the intrinsic aggregation-caused quenching feature of the fluorophores. A conformationally twisted pyridyl π-conjugate as a solid-state emitter is appended with well-known and inexpensive poly(methylmethacrylate) [PMMA] to afford a handy, portable, and reusable solid-state emitting polymer matrix. Entrapment of the probe is noticed through non-covalent interactions, resulting in a green-emitting platform. It quickly accepts a proton upon acid vapor exposure and switches emission from green to red with a significant 107nm redshift. This shift is reversible with red to green emissions while exposed to base vapor. Thus, polymer-blended, homogeneous red-emitting pyridyl salt is employed as potential material to detect various basic vapors optically. Among different bases, naked-eye detection of essential analytes such as ammonia vapor and melamine shows potential demands. Hence, we have established an easy detection of ammonia vapor and aqueous melamine as low as 2.5 and 0.126ppm, respectively, using this solid-state emitter that displays an emission color change with an enhancement of emission intensity even in an aqueous solution.

Color-Tunable Binary Copolymers Manipulated by Intramolecular Aggregation and Hydrogen Bonding.

Construction of color-tunable luminescent polymeric materials with enhanced emission intensity and room-temperature phosphorescence (RTP) performance regulated by a single chromophore component is highly desirable in the scope of photoluminescent materials. Herein, a set of binary copolymers were facilely synthesized using free radical polymerization by selecting different types of polymer matrix and N-substituted naphthalimides (NPA) as chromophores. Surprisingly, the fluorescence emission of copolymers could be remarkably enhanced, because of the intramolecular aggregation of NPA manipulated by a single polymer chain in both solution and solid state. Moreover, RTP signals of binary copolymers were all clearly observed in the air without any processing procedure, because of the embedding of phosphors into hydrogen bonding networks after copolymerization with vinyl-based acrylamide monomers. Taking advantages of the synergistic effect of copolymerization-induced aggregation and copolymerization-induced rigidification to promote optical performance, UV stimulus-responsive luminescent polymer films with processability, flexibility, and adjustable emission wavelength were simply prepared using a drop-casting method in large scale, the setting of which is the basis for application in the fields of organic optoelectronics, information security, and bioimaging/sensing.

Enhanced luminescence and Judd-Ofelt analysis in SiO2 encapsulated CaWO4@CaWO4:Eu:Bi for visualization of latent fingerprints and anti-counterfeiting

Core nanoparticles (NPs) and core–shell particles have been synthesized using the low temperature reflux method. The structural and photo-physical properties of the developed phosphors have been investigated through various analytical techniques. The transmission electron microscopy (TEM) analysis evidences the formation of the shell on the core NPs. The optical band gap is estimated using the diffuse reflectance spectra. An 8-fold enhancement of emission intensity is observed in the core–shell particles as compared to that of core, due to the reduced surface quenchers after silica coating. In addition, the Judd-Ofelt (J-O) parameters have been calculated to reveal the site symmetry and coordination environment around Eu3+ ions. The tunable red emission on formation of core–shell structures is confirmed from the CIE diagram. These results are ascribed to the formation of the chemical bonds between CaWO4@ CaWO4:3%Eu3+:5%Bi3+ (core) and amorphous SiO2 shell via W – O – Si bridges. Better hydrophilicity developing from active functional groups in solutions and intense luminescence behavior with a quantum efficiency of 91% allow the developed phosphors for various potential applications such as solid state lighting, bio-labelling agent for the visualization of latent fingerprints (LFPs) and anti-counterfeiting, etc.

Upconversion luminescence studies in (Er3+, Yb3+, and Mo6+) tri-doped SrWO4 ceramics

Augmented sensitization in (Er3+, Yb3+, and Mo6+) tri-doped SrWO4 ceramic compositions is investigated, and the possible role of [Yb-MoO4]2- dimer formation is probed. Structural distortion in SrO8 deltahedron and WO4 tetrahedral units in SrWO4 due to Er–Yb ion substitution for Sr2+, and Mo6+ for W6+ is confirmed by Rietveld refinement of X-ray diffraction data. Evolution of defect induced phase depending on Mo6+ dopant concentration, and the formation of [Yb-MoO4]2- dimer is envisaged by Raman and infrared spectroscopy. Selective enhancement in the green emission band (530 nm) by ∼ 58 times is supported by [Yb-MoO4]2- dimer development, and the enhancement of up-conversion emission intensity is confirmed using excited state decay life time measurements.

Spectral Tuning, Stabilities under External Exposures, and Spontaneous Enhancement of Emission Intensity in Grown‐into‐Glass All‐Inorganic Metal Halide Perovskite Nanocrystals

AbstractHerein, the grown‐into‐glass (GIG) CsPbBr3:Ln3+ (Ln = La, Lu) nanocrystals (NCs) are designed and fabricated using an in situ nanocrystallization method. It is shown that a substitution of Pb2+ sites with Ln3+ ions leads to a blueshift of emission position induced by an increase of the bandgap of CsPbBr3. Additionally, the GIG‐samples are found to feature excellent photoluminescent (PL) properties after being immersed respectively in water for 300 days at room temperature, boiling water for 12 h, and corrosive environments for 24 h, as well as recoverable PL intensity either after several cycles of heat‐cooling experiments or after being continuously exposed to a 405 nm laser irradiation. Besides, a spontaneous enhancement of 20‐25% of emission intensity during the 1‐2.5 hours' stage of a 405 nm laser irradiation, attributed to the radiative recombination of charge carriers that can be de‐trapped from trapping levels upon the laser light irradiation and that then spontaneously reinforces the emission intensity, is observed in the GIG‐CsPbBr3:Ln3+ NCs. Finally, a white light‐emitting prototype, with a CIE chromaticity coordinate at (0.4110, 0.3706), a color rendering index of 89 and a correlated color temperature of 3363 K is realized by combining the GIG‐CsPbBr3 NCs, YAG:Ce and CaWO4:Eu phosphors.

Tailored light emission from color centers in nanodiamond using self-assembled photonic crystals

The defect centers in solid-state materials especially the nitrogen-vacancy (NV) centers in diamond have shown a tremendous potential for their utilization in quantum technology applications. However, they exhibit certain drawbacks such as the feeble zero phonon line with huge phonon contribution and the higher lifetime values. Here, we present a novel approach to control the spontaneous emission from NV centers in nanodiamond using engineered self-assembled photonic crystals. Using two complimentary emission measuring geometries at room temperature, we show a 63% suppression and 17% enhancement of NV center emission intensity using photonic stopgap, supported with simulations. The emission rates are modified in a broad spectral range of NV center emission and are consistent with the Barnett–Loudon sum rule. The results are crucial for emerging quantum technologies using NV centers in diamond.

Precursor sources dependent formation of colloidal CdSe quantum dots for UV-LED applications

We have presented varied shaped CdSe nanoparticles (NPs) synthesized by solution-based one-pot hot injection colloidal method by varying the precursor salt of Cd (i.e., cadmium oxide, cadmium chloride, and cadmium acetate) at an optimized Cd/Se ratio (2:1). CdSe nanoparticles of varied shapes and sizes (5–25 nm) were synthesized by using Butylamine and Octadecene as capping ligands and the nucleation and growth mechanism has been explained using LaMer’s diagram. It has been found that Butyl amine owing to its improved capping effect and better surface-traps passivation, aids in emission intensity enhancement of CdSe QD’s. The optical properties of the as-synthesized CdSe colloidal NPs have been investigated in terms of quantum confinement effects to reveal their suitability as a pursuing material for UV-LED. Variation in the morphology of CdSe NPs synthesized using different precursor sources leads to changes in the bandgap for its potential application in QD-based LEDs. To the best of the author’s knowledge, this is the first-hand report on the synthesis of CdSe QD’s from varied Cd-precursor sources using butyl amine and octadecene as capping ligands via hot injection technique for UV-LED applications.

Efficient Single-Photon Sources Based on Chlorine-Doped ZnSe Nanopillars with Growth Controlled Emission Energy.

Isolated impurity states in epitaxially grown semiconductor systems possess important radiative features such as distinct wavelength emission with a very short radiative lifetime and low inhomogeneous broadening, which make them promising for the generation of indistinguishable single photons. In this study, we investigate chlorine-doped ZnSe/ZnMgSe quantum well (QW) nanopillar (NP) structures as a highly efficient solid-state single-photon source operating at cryogenic temperatures. We show that single photons are generated due to the radiative recombination of excitons bound to neutral Cl atoms in ZnSe QW and the energy of the emitted photon can be tuned from about 2.85 down to 2.82 eV with ZnSe well width increase from 2.7 to 4.7 nm. Following the developed advanced technology, we fabricate NPs with a diameter of about 250 nm using a combination of dry and wet-chemical etching of epitaxially grown ZnSe/ZnMgSe QW structures. The remaining resist mask serves as a spherical- or cylindrical-shaped solid immersion lens on top of NPs and leads to the emission intensity enhancement by up to an order of magnitude in comparison to the pillars without any lenses. NPs with spherical-shaped lenses show the highest emission intensity values. The clear photon-antibunching effect is confirmed by the measured value of the second-order correlation function at a zero time delay of 0.14. The developed single-photon sources are suitable for integration into scalable photonic circuits.

Sc3+-induced double optimization strategies for boosting NIR-II luminescence and improving thermometer performance in CaF2: Nd3+, Nd3+/Yb3+@NaYF4 nanocrystals

Lanthanide-based near-infrared-emitting nanocrystals have aroused enormous attention for their promising applications in biomedical imaging and temperature sensing. However, the concentration quenching effect and energy migration to surface quenchers are inevitable parts of the lanthanide doped systems, which cause a low signal-to-noise ratio of detection. Herein, we delicately design CaF2: Nd3+/Sc3+@NaYF4 nanocrystal, in which the Sc3+ ions are introduced to block the cross relaxation between adjacent Nd3+ ions, and the buffer layer of NaYF4 can suppress surface defects, resulting in 10-fold higher photoluminescence at 1060 nm compared to CaF2: Nd3+ nanocrystal under 808 nm excitation. Besides, CaF2: Nd3+/Yb3+ as a ratiometric luminescence nanoprobe is optimized through additional Sc3+ to enhance emission intensity and tune thermal sensitivity, which allows precise detection of temperature. This work not only provides a feasible strategy to design efficient near-infrared-emitting lanthanide nanocrystals, but also opens up enormous potential of high-sensitivity ratiometric nanothermometers in nanomedicine.

Spying on the peroxynitrite fluctuation during hearing loss enabled by rationally designed fluorescent carbon dots

Hearing loss is a common type of sensory deprivation. Peroxynitrite (ONOO−) is a biologically generated reactive oxygen species that can behave as a deleterious species due to its abnormal regulation associated with the pathogenesis of many human diseases, including hearing loss. Despite the importance of ONOO− and its biological functions, accurate detection methods for monitoring ONOO− in real time and exploring the roles of ONOO− in living systems are lacking. Herein, we report a novel carbon dots (CDs)-based fluorescence turn-on ONOO− probe for tracking endogenous and exogenous ONOO− produced by RAW264.7 cells. The probe exhibited considerably enhanced emission intensity, fast response rate, outstanding selectivity, and good sensitivity. Owing to these attractive sensing properties, peroxynitrite fluctuations in a hearing loss model were monitored for the first time. Therefore, CDs are potentially effective tools for assessing fluctuations in ONOO− under different physiological and pathological conditions.

Enhancement of Emission from Lanthanide Dopants in Perovskite Nanocrystals through a Temperature-Dependent Phase Transformation of the Perovskite Lattice

The excited states of lanthanide ions (Ln3+) exhibit ultranarrow emission and long spin dephasing lifetimes suitable for optoelectronic and quantum applications but are not directly optically accessible. One effective strategy to excite Ln3+ ions is to dope them into a semiconductor host lattice, which acts as a photosensitizer. This work describes enhancement of emission intensity by a factor of 19 with decreasing temperature (from 300 to 5 K) from Sm3+ ions in CsPbCl3 nanocrystal hosts. Structural characterization over the same temperature region reveals that this enhancement is primarily due to a symmetry-lowering cubic-to-orthorhombic phase transition of the host lattice, which reduces the local site symmetry of the dopant and increases the Sm3+* emission quantum yield.

A New High Selective and Sensitive Fluorescent Probe for Al3+ based on Photochromic Salicylaldehyde Hydrazyl Diarylethene.

A new diarylethene derivative 1O decorated with a salicylaldehyde hydrazine moiety was designed and synthesized successfully, and its structure was confirmed by NMR. Diarylethene 1O showed eminent photochromism and high selectivity and sensitivity for Al3+ with turn-on fluorescent performance. As the concentration of Al3+ in 1O solution increased, the color of solution remarkably changed from dark to bright green with 313-fold fluorescent emission intensity enhancement. The 1:1 combination stoichiometry between 1O and Al3+ was verified by Job's plot and MS analysis. The association constant between 1O and Al3+ was 3.9 × 102mol-1 L, and the limit of detection toward Al3+ was 7.98 × 10-9mol L-1. Meanwhile, the probe can be utilized in practical water and logic circuits.

Investigation of TiO2 and Ce3+-activated TiO2 particles on optical properties of the PMMA embedded YAG: Ce3+ and LuAG: Ce3+

Ce3+ activated garnets; LuAG and YAG are extensively used in lighting applications, electronics, and display technologies. Both of the phosphors have been studied many times to increase their brightness and provide a red-shift in their emission maximum towards warmer colors for potential white light emitting diode (WLED) applications. In this work, binary blends of the LuAG: Ce3+ with the micro-scale TiO2 and Ce3+-equipped TiO2 particles were prepared and tested in terms of photoluminescence characteristics in a polymethyl methacrylate (PMMA) matrix. Similar work was also performed for the YAG: Ce3+and its TiO2-based composites. Blue-wavelength excitation and emission performances as well as decay characteristics of the phosphors were investigated in detail. When excited by blue wavelengths, the TiO2 blends of the LuAG: Ce3+ and YAG: Ce3+ exhibited strong enhancement in emission intensities extending to 2.80 and 2.20 fold in comparison to their additive-free forms. Additionally, 32 and 66 nm of red shifts were measured in the emission maximum of the TiO2-based blends, respectively. The decay time measurements performed in the microsecond time scale revealed parallel variations to the increases observed in the intensities. The distinguishable enhancement observed in the quantum efficiency of the phosphors by using cost-effective TiO2 particles can be concluded as a remarkable development. Additionally, the ability of the phosphor blends to be excited with simple blue LEDs looks very promising for future lighting applications.

Super‐Resolution Lifetime Imaging of Single Molecules Near Gold Bowtie Nanoparticles

AbstractInteractions between light and matter serve as the basis of many technologies, but the quality of these devices is inherently limited by the optical properties of their constituents. Plasmonic nanoparticles are a highly versatile and tunable platform for the enhancement of such optical properties. However, the near‐field nature of these effects has made thorough study and understanding of these mechanisms difficult. In this work, we introduce a fully confocal technique combining photoswitching super‐resolution microscopy with fluorescence lifetime imaging microscopy to study single‐molecule decay rate enhancement. We demonstrate that the technique combines a spatial resolution better than 20 nm, and a 16 ps temporal resolution. Simultaneously, an autocorrelation measurement is also performed to confirm that the data indeed originates from single molecules. This work provides insight into the various mechanisms of plasmon‐enhanced emission, and allows the study of the correlation between emission intensity and lifetime enhancement. This complicated relationship is shown to be dependent upon the relative influence of various radiative and nonradiative decay pathways. Here, we provide a platform for further study of emission mislocalization, the position‐dependent prominence of different decay pathways, and the direct super‐resolved measurement of the local density of states.

Self‐Standing Membrane of Hetero‐Assembled Nanosheets with Drastically Enhanced Emission and Tunable Color

AbstractSelf‐standing membranes are fabricated by filtrating corresponding superlattice units of luminescent rare‐earth hydroxide (e.g., europium doped gadolinium hydroxide (GdEu), terbium doped gadolinium hydroxide (GdTb)) nanosheets, and semiconducting oxide (e.g., Ti0.87O20.52− (TiO), TaO3− (TaO)) nanosheets. The superlattice membrane of GdEu/TiO and GdTb/TaO shows drastically enhanced emission intensity 21.5 and 38.6 times higher than that of GdEu and GdTb, respectively, as well as a higher color purity and longer lifetime. By further integrating both GdEu/TiO and GdTb/TaO superlattices, the (GdEu/TiO)/(GdTb/TaO) integrated membrane exhibits tunable color under different excitations. The superior performance is ascribed to the enhanced energy absorption by the semiconducting oxide nanosheets and efficient energy transfer to rare‐earth hydroxide nanosheets across the nanointerface. Moreover, the superlattice membrane displays strong and stable cathodoluminescence under continuous cathode‐ray radiation. This work demonstrates a new strategy for large‐scale fabrication of self‐standing membranes, which are promising for practical applications in multicolor display fields.

Exploring the binding mechanism of amine-functionalized tetraaryl imidazole fluorescent ligands with lipase: Insights from multi-spectroscopic, thermodynamic and docking approaches

Environment-sensitive fluorescence ligands based on twisted intramolecular charge transfer (TICT) are often applied to target relevant biomacromolecules. In this work, several imidazole-based “D-π-A” fluorescent ligands with different amine side chains have been designed, which showed sensitivity toward solvent polarity and viscosity. The binding of obtained ligands with lipase led to enhancement of emission intensity. Results from binding parameters exhibited that the ligands bound with lipase in a 1:1 stoichiometry, and the flexible amine side chain appended ligand was more sensitive to lipase. The fluorescence quenching experiments of ligands with lipase suggested the involvement of a static quenching mechanism in the binding process. From the estimated thermodynamic parameters, complexation between the ligands and lipase was found to occur primarily via Van der Waals forces and hydrogen bonds formation. Observations from synchronous, 3D fluorescence and CD spectra pointed that the binding of ligands to lipase impacted the microenvironment around tyrosine and typtophan residues, but was not enough to change the secondary structure of lipase. Moreover, modeling calculation demonstrated that ligands were mainly located within the hydrophobic pockets of lipase. This study provides evidence for expanding the application of environment-sensitive fluorescent ligands for probes or drug candidates targeting lipase.

Spontaneous emission enhancement based on thin-film chalcogenide/fluoride one dimensional photonic crystal

We report the fabrication of a one-dimensional photonic crystal microcavity via co-evaporation with electron beam/thermal evaporation process, which, to the best of our knowledge, is the first rare-earth doped one-dimensional photonic crystal based on chalcogenide/fluoride thin films. The microcavity was made of a half-wave dysprosium doped Ga2Se3 layer sandwiched between two embedded Ga2Se3/YF3 distributed Bragg reflectors. Near infrared transmittance spectra indicated that the stopband region from 1090 nm to 1515 nm was formed and a cavity resonance centered at 1342 nm. A cavity quality factor of 153 was achieved resulting in a 53-fold enhancement in spontaneous emission intensity. This photonic crystal microcavity configuration offers a new route to mid-wavelength and long-wavelength infrared fluorescence enhancement, which has attracted considerable interest for potential applications, such as fluorescence-based imaging and biomedical sensing.