Time-resolved measurement of atomic emission enhancement by fs-ns dual-pulsed laser-induced breakdown spectroscopy

Time-resolved measurement of atomic emission enhancement is performed by using a 500-fs KrF laser pulse incident upon a high density supersonic O2 gas jet, synchronized with an orthogonal ns frequency-doubled Nd：YAG laser pulse. The ultra-short pulse serves as an igniter of the gas jet, and the subsequent ns-laser pulse significantly enhances the atomic emission. Analysis shows that the contributions to the enhancement effect are made mainly by the bremsstrahlung radiation and cascade ionization.

Fluorescence Emission Mediated by Metal-Dielectric-Metal Fishnet Metasurface: Spatially Selective Excitation and Double Enhancement

Enhancement of uorescent radiation is of great importance for applications including biological imaging,high-sensitivity detectors,and integrated light sources.Strong electromagnetic elds can be created around metallic nanoparticles or in gap of nanostructures,where the local state density of radiating mode is then dramatically enhanced.While enhanced uorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs,simultaneous mediation of absorption and emission processes of uorescent emitters remains challenging in metallic nanostructures.Here,we investigate uorescent emission mediated by metal-dielectric-metal fishnet metasurface,in which localized surface plasmon(LSP)and magnetic plasmon polaritons(MPPs)modes are coupled with absorption and emission processes,respectively.For absorption process,coupling of the LSP mode enables spatially-selective excitation of the uorescent emitters by rotating the polarization of the pump laser beam.In addition,the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the uorescent emission by introducing a rectangular fishnet structure.All the experimental observations are further corroborated by nite-difference time-domain simulations.The structure reported here has great potential for application to color light-emitting devices and nanoscale integrated light sources.

Phase Transformation and Enhancing Electron Field Emission Properties in Microcrystalline Diamond Films Induced by Cu Ion Implantation and Rapid Annealing

Cu ion implantation and subsequent rapid annealing at 500℃ in N2 result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm2 V-1S-1 for microcrystalline diamond （MCD） films. Its electrical field emission behavior can be turned on at Eo = 2.6 V/μm, attaining a current density of 19.5μA/cm2 at an applied field of 3.5 V/#m. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron mi- croscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation.

Pressure-induced emission(PIE)in halide perovskites toward promising applications in scintillators and solid-state lighting

High-pressure chemistry has provided a huge boost to the development of scientific community.Pressure-induced emission(PIE)in halide perovskites is gradually showing its unique charm in both pressure sensing and optoelectronic device applications.Moreover,the PIE retention of halide perovskites under ambient conditions is of great commercial value.Herein,we mainly focus on the potential applications of PIE and PIE retention in metal halide perovskites for scintillators and solid-state lighting.Based on the performance requirements of scintillator and single-component white light-emitting diodes(WLEDs),the significance of PIE and PIE retention is critically clarified,aiming to design and synthesize materials used for high-performance optoelectronic devices.This perspective not only demonstrates promising applications of PIE in the fields of scintillators and WLEDs,but also provides potential applications in display imaging and anti-counterfeiting of PIE materials.Furthermore,solving the scientific disputes that exist under ambient conditions is also simply discussed as an outlook by introducing high-pressure dimension to produce PIE.

Two different emission enhancement of trans-stilbene crystal under high pressure: Different evolution of structure

Mechanoresponsive luminescent(MRL)materials have drawn extensive concern due to their potential applications in mechanical sensors,memory chips,and security inks;especially these possessing high emission efficiency.In this work,we found trans-stilbene crystal exhibited two different pressure-induced emission enhancement(PIEE)behaviors at different pressure areas.The structural characterizations combined with density functional theory calculation indicate that the first emission enhancement was due to the decrease of nonradiation transition by the weaken of energy exchange process between atoms and lattice.And the second emission enhancement was attributed to the strengthen of C-H...C interactions from the non-planarization comformation.The results regarding the mechanoresponsive behavior of trans-stilbene offered a deep insight into PIEE from the structural point of view,which will facilitate the design of and search for high-performance MRL materials.

Enhancement of optical emission generated from femtosecond double-pulse laser-induced glass plasma at different sample temperatures in air

In double-pulse laser-induced breakdown spectroscopy(DP-LIBS), the collinear femtosecond double-pulse laser configuration is experimentally investigated with different initial sample temperatures using a Ti:sapphire laser. The glass sample is ablated to produce the plasma spectroscopy. During the experiment, the detected spectral lines include two Na(I) lines(589.0 nm and 589.6 nm) and one Ca(I) line at the wavelength of 585.7 nm. The emission lines are measured at room temperature(22 ℃) and three higher initial sample temperatures(T_s?=?100 ℃, 200 ℃, and 250 ℃). The inter-pulse delay time ranges from-250 ps to 250 ps.The inter-pulse delay time and the sample temperature strongly influence the spectral intensity,and the spectral intensity can be significantly enhanced by increasing the sample temperature and selecting the optimized inter-pulse time. For the same inter-pulse time of 0 ps(single-pulse LIBS), the enhancement ratio is approximately 2.5 at T_s?=?200 ℃ compared with that obtained at T_s?=?22 ℃. For the same inter-pulse time of 150 ps, the enhancement ratio can be up to 4 at T_s?=?200 ℃ compared with that obtained at T_s?=?22 ℃. The combined enhancement effects of the different initial sample temperatures and the double-pulse configuration in femtosecond LIBS are much stronger than that of the different initial sample temperatures or the double-pulse configuration only.

Supramolecular cyclization induced emission enhancement in a pillar[5]arene probe for discrimination of spermine

Early diagnosis and treatment of cancer requires the development of tools that are both sensitive and selective in detecting spermine.In this study,we presented a"supramolecular cyclization-induced emission enhancement"strategy for the sensitive and selective detection of spermine.A new pillar[5]arene probe(P1)demonstrated excellent solution/solid dual-state emission properties,and the addition of certain spermine(Spm)resulted in fluorescence enhancement due to the synergy of multiple weak interactions that restricted the free motion of P1 in the P1⊃Spm complex.This mechanism was further confirmed by time-resolved spectroscopy,DFT calculations,and IGM analysis.With its low limit of detection and high selectivity,P1 is a promising tool for measuring spermine in artificial urine samples.

Co-optimization of carbon dioxide storage and enhanced oil recovery in oil reservoirs using a multi-objective genetic algorithm(NSGA-Ⅱ)

Climate researchers have observed that the carbon dioxide （CO2） concentration in the atmosphere have been growing significantly over the past century. CO2 from energy represents about 75% of the greenhouse gas （GHG） emissions for Annex B （Developed） countries, and over 60% of global emissions. Because of impermeable cap rocks hydrocarbon reservoirs are able to sequester CO〉 In addition, due to high-demand for oil worldwide, injection of CO2 is a useful way to enhance oil production. Hence, applying an efficient method to co-optimize CO2 storage and oil production is vital. Lack of suitable optimization techniques in the past led most multi-objective optimization problems to be tackled in the same way as a single objective optimization issue. However, there are some basic differences between the multi and single objective optimization methods. In this study, by using a non- dominated sorting genetic algorithm （NSGA-II） for an oil reservoir, some appropriate scenarios are proposed based on simultaneous gas storage and enhanced oil recovery optimization. The advantages of this method allow us to amend production scenarios after implementing the optimization process, by regarding the variation of economic parameters such as oil price and CO2 tax. This leads to reduced risks and time duration of making new decisions based on upcoming situations.

Magnetic emission intensity enhancement for amorphous alloys by constructing a multi-phase structure withα-Fe nanocrystals

The perturbation in the magnetic field generated by the rotation or oscillation of magnetic domains in magnetic materials can emit low-frequency electromagnetic waves,which are expected to be used in low-frequency communications.However,the magnetic emission intensity,defined by the perturbation ability,of current commercially applied amorphous alloys,such as Metglas,cannot meet the application requirements for low-frequency antennas due to the domain motion energy loss.Herein,a multi-phase Metglas amorphous alloy was constructed by incorporatingα-Fe nanocrystals using rapid annealing to manipulate the domain movement.It was found that 3.89 times higher magnetic emission intensity is obtained compared to the pristine due to the synergism of the deformation and displacement mechanisms.Moreover,the low-frequency magnetic emission performance verification was carried out by preparing magnetoelectric composites as the antenna vibrator by assembling the alloy and macro piezoelectric fiber composites(MFC).Enhancements of magnetic emission intensity are found at 93.3%and 49.2%at the first and second harmonic frequencies compared with the unmodified alloy vibrator.Therefore,the approach leads to the development of high-performance communication with a novel standard for evaluation.

Multiple Nodeless Superconducting Gaps in （Ba0.6K0.4）Fe2As2 Superconductor from Angle-Resolved Photoemission Spectroscopy

High resolution angle-resolved photoemission measurements have been carried out to study the superconducting gap in the （Ba0.6K0.4）Fe2As2 superconductor with Tc=35 K. Two hole-like Fermi surface sheets around the F point exhibit different superconducting gaps. The inner Fermi surface sheet shows larger （10 - 12 meV） and slightly momentum-dependent gap while the outer one has smaller （7 - 8 meV） and nearly isotropic gap. The lack of gap node in both Fermi surface sheets favours s-wave superconducting gap symmetry. Superconducting gap opening is also observed at the M（π, π） point. The two Fermi surface spots near the M point are gapped below Tc but the gap persists above Tc. The rich and detailed superconducting gap information will provide key insights and constraints in understanding pairing mechanism in the iron-based superconductors.

Enhanced Photoluminescence of InGaN/GaN Green Light-Emitting Diodes Grown on Patterned Sapphire Substrate

Green InGaN/GaN based light-emitting diodes （LEDs） are fabricated both on planar and wet-etched patterned sapphire substrates by metalorganic vapour phase epitaxy （MOVPE）. Their photoluminescence （PL） properties of the two samples are studied. The results indicate that the PL integral intensity of the green LED on the patterned substrate is nearly two times of that on the planar one within the whole measured temperature range. The enhanced PL intensity in the green LED on the patterned substrate is shown completely contributed from the extraction efficiency, but not from the internal quantum efficiency. The conclusion is supported by temperature-dependent PL analysis on the two samples, and the mechanisms axe discussed.

Gold Nanostars-AIE Theranostic Nanodots with Enhanced Fluorescence and Photosensitization Towards Effective Image-Guided Photodynamic Therapy

Dual-functional aggregation-induced photosensitizers(AIE-PSs)with singlet oxygen generation(SOG)ability and bright fluorescence in aggregated state have received much attention in image-guided photodynamic therapy(PDT).However,designing an AIE-PS with both high SOG and intense fluorescence via molecular design is still challenging.In this work,we report a new nanohybrid consisting of gold nanostar(AuNS)and AIE-PS dots with enhanced fluorescence and photosensitization for theranostic applications.The spectral overlap between the extinction of AuNS and fluorescence emission of AIE-PS dots(665 nm)is carefully selected using five different AuNSs with distinct localized surface plasmon(LSPR)peaks.Results show that all the AuNS s can enhance the 1 O2 production of AIE-PS dots,among which the AuNS with LSPR peak at 585 nm exhibited the highest 1 O2 enhancement factor of15-fold with increased fluorescence brightness.To the best of our knowledge,this is the highest enhancement factor reported for the metalenhanced singlet oxygen generation systems.The Au585@AIE-PS nanodots were applied for simultaneous fluorescence imaging and photodynamic ablation of HeLa cancer cells with strongly enhanced PDT efficiency in vitro.This study provides a better understanding of the metal-enhanced AIE-PS nanohybrid systems,opening up new avenue towards advanced image-guided PDT with greatly improved efficacy.

Liver metastases:Contrast-enhanced ultrasound compared with computed tomography and magnetic resonance

The development of ultrasound contrast agents with excellent tolerance and safety profiles has notably improved liver evaluation with ultrasound(US)for several applications,especially for the detection of metastases.In particular,contrast enhanced ultrasonography(CEUS)allows the display of the parenchymal microvasculature,enabling the study and visualization of the enhancement patterns of liver lesions in real time and in a continuous manner in all vascular phases,which is similar to contrast-enhanced computed tomography(CT)and contrast-enhanced magnetic resonance imaging.Clinical studies have reported that the use of a contrast agent enables the visualization of more metastases with significantly improved sensitivity and specificity compared to baseline-US.Furthermore,studies have shown that CEUS yields sensitivities comparable to CT.In this review,we describe the state of the art of CEUS for detecting colorectal liver metastases,the imaging features,the literature reports of metastases in CEUS as well as its technique,its clinical role and its potential applications.Additionally,the updated international consensus panel guidelines are reported in this review with the inherent limitations of this technique and best practice experiences.

Strong Band-Edge Emission from ZnS Quantum Dots Stabilized by Gum Arabic

ZnS quantum dots （QDs）, prepared by soft-condensation, exhibit robust structure of a quantum size equal 3.13 nm mediated two-dimensional gum Arabic surfactant as characterized by scan tunnelling microscope （STM）. Strong blue-shifted absorption and emission bands are depicted by optical characterization even for the sample stored under ambient condition for two weeks. These enhancements can be attributed to the completely passivated surface trap states by Gum Arabic.

Conical Emission Patterns by Femtosecond Pulses with Different Spectral Bandwidths

Different conical emission （CE） patterns are obtained experimentally at various incident powers and beam sizes of pump laser pulses with pulse durations of 7fs, 44fs and 100fs. The results show that it is the incident power but not the incident power density that determines a certain CE pattern. In addition, the critical powers for similar CE patterns are nearly the same for the laser pulses with the same spectral bandwidth. Furthermore, as far as a certain CE pattern is concerned, the wider the spectral bandwidth of pump laser pulse is, the higher the critical power is. This will hopefully provide new insights for the generation of CE pattern in optical medium.

Simple method to rapidly fabricate chain-like carbon nanotube films and its field emission properties

A simple process to fabricate chain-like carbon nanotube （CNT） films by microwave plasma-enhanced chemical vapor deposition （MPCVD） was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.

Electric-Wiggler-Enhanced Three-Quantum Scattering and the Output Power Affected by this Scattering in a Free-Electron Laser

We derive the cross section of scattering through the three-quantum interaction of an electron with the incident laser field, the emitted photon, and an axial electrostatic field produced by the magnetic wiggler in the magnetic wiggler acting as the sole zeroth-order perturbing classical field in the first free-electron laser （FEL）. In the derivation, we apply quantum-wiggler electrodynamics （QWD）. We find that this scattering predominates the usual two-quantum scattering. The output power of spontaneous free-electron two-quantum Stark emission driven by the above electrostatic field attenuated by the three-quantum scattering agrees within a factor of 10 with the measured power in the case of the first FEL.

Amplified Spontaneous Emission of Organic Pyridinium Dye doped Polymeric Waveguide

An organic dye salt trans-4-[p-（N-hydroxyethyl-N-methylamino）styryl]-N-methylpyridinium iodide （ASPI） is doped with an electron transport organic molecule tris（8-hydroxyquinoline） aluminium （Alq3） in a host matrix of poly（methylmethacrylate） （PMMA）, and the amplified spontaneous emission （ASE） is studied. By efficient Forster energy transfer from Alq3 to ASPI, it is demonstrated that the ASE threshold of ASPI：Alq3：PMMA waveguide （about 11 μJ/pulse） is much lower than that of ASPI：PMMA system （about 38 μJ/pulse）. Meanwhile, the peak position of ASE can be controlled by the effect of film thickness on waveguide modes. We show that the ASE peak position can be tuned over 37nm. These characteristics indicate the ASPI：Alq3 system as a promising gain medium for optical amplifiers and organic semiconductor lasers.

Low-field electron emission from pinaster-like MoO_2 nanoarrays as two-stage emitters

Low-field electron emission is obtained from the pinaster-like MoO2 nanoarrays. The turn-on field of the pinasterlike MoO2 nanoarrays is found to be as low as 2.39 V/μm with the current density of 10μA/cm2. The enhancement factor is extracted to be 3590 from the Fowler-Nordheim plot. These excellent emission properties are attributed to the special structure of the pinaster-like MoO2 nanoarrays and confirmed by the calculation in the frame of the two -stage model. Our results show that the pinaster-like MoO2 nanoarrays are promising candidate in realizing field emission displays.

Field emission of carbon nanotube array with normal-gate cold cathode

A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and the emission electron beam becomes a column. The field enhancement factor and the emission current intensity step up greatly compared with those of the diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.