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Synthesis, energy transfer mechanism, and tunable emissions of novel Na3La(VO4)2:Re3+ (Re3+ = Dy3+, Eu3+, and Sm3+) vanadate phosphors for near-UV-excited white LEDs
摘要： In this study, novel Eu3+-, Dy3+-, and Sm3+-activated Na3La(VO4)2 phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na3La(VO4)2 phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O8 and La(2)O8 polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na3La(VO4)2 compound was an excellent host for activating the luminescence of Eu3+ (614 nm), Dy3+ (575 nm), and Sm3+ (647 nm) ions. Further, Dy3+/Eu3+ co-doped Na3La(VO4)2 phosphors were exploited, and the energy transfer from Dy3+ to Eu3+ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy3+ to Eu3+ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy3+/Eu3+ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.
关键词： Vanadate phosphor,White LED,Energy transfer,Lighting and display,Near ultraviolet excitation,Tunable emissions
更新于2025-09-16 10:30:52
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Selective excitation of one among the three peaks of tip‐enhanced Raman spectroscopy by a shaped ultrafast laser pulse
摘要： There are generally several neighboring Raman peaks that are excited simultaneously in tip‐enhanced Raman spectroscopy (TERS). A method to selectively excite a specific Raman peak and simultaneously depress the others is required for suppressing noise and improving detection sensitivity and accuracy. In this study, we demonstrate a scheme for selective excitation of one Raman peak among three excited states in TERS by properly shaping the pump and Stokes femtosecond laser pulses. The shaped pump and Stokes pulses are transformed into time domain, discretized and reconstructed; they are then used to irradiate the TERS structure obliquely. The impulse responses at five probe points of the TERS structure are calculated followed by a Fourier transform. In these cases, the probability of one selectively excited Raman transition increases by several hundreds to tens of thousands in amplitude, whereas the others are both depressed to zero. The probe points at different positions in the tip apex do not affect the enhanced and selective excitation of one Raman transition among the three excited states.
关键词： tip‐enhanced Raman spectroscopy,femtosecond laser pulse shaping,selective excitation
更新于2025-09-16 10:30:52
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Decay Kinetics of Thermal Radiation Emitted by Surface Layers of Carbon Materials under Pulsed Laser Excitation
摘要： The decay of thermal radiation emitted by surface layers of carbon materials excited by pulses of a Q-switched neodymium laser is investigated experimentally and theoretically. It is discovered that the decay curves can be approximated with satisfactory accuracy by a sum of two exponential components with decay times of about 10 and 100 ns. Changes in the decay curves under sample irradiation by a sequence of laser pulses can be interpreted as being the result of redistribution of intensities of these two components. Based on the results of computer simulation, the conclusion is drawn that the glow-decay time is determined by the ratio of the penetration depth of the laser radiation and the thermal-diffusion length, which creates an opportunity to determine the coefficient of temperature conductivity in a thin surface layer of the studied material at high temperatures (thousands of Kelvins).
关键词： decay kinetics,temperature conductivity,pulsed laser excitation,carbon materials,thermal radiation
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Polarisation-Resolved Investigations of the Pico- and Nanosecond Dynamics of Broad Area Distributed Bragg Reflector Lasers under Very High-Current Pulse Excitation
摘要： Diode lasers generating optical pulses with high peak power and pulse lengths in the pico- and nanosecond ranges are key components for LiDAR (Light Detection and Ranging) systems, e.g., for autonomous driving and object detection and other applications such as free-space communication, metrology, material processing and spectroscopy [1,2]. For automotive LiDAR systems short optical pulses (100 ps - 10 ns) with high pulse powers, low wavelength shift with temperature and good beam quality are needed [3,4]. To achieve this, we have developed and investigated distributed Bragg reflector (DBR) broad area (BA) lasers having an InGaAs single quantum well active region embedded non-centred in the AlGaAs confinement layer. The total cavity length is 6 mm, the DBR length 1 mm and the lateral aperture is defined by an etched mesa with a width of 60 μm. The vertical divergence is about 25° (FWHM) and the emission wavelength is 905 nm at 25°C. The laser diodes soldered p-side down on CuW submonts are mounted into a new in-house developed high-speed unit and are electrically driven by nearly rectangular shaped 1 ns to 10 ns long current pulses with very high amplitudes up to 120 A corresponding to a current density of about 40 kA/cm2. The aim of this contribution is to present for the first time experimental polarisation-resolved investigations of the complicated spatio-spectral-temporal behaviour of the laser emission under these high excitation conditions in the time range 100 ps – 10 ns.
关键词： LiDAR,Diode lasers,distributed Bragg reflector,broad area lasers,high-current pulse excitation
更新于2025-09-16 10:30:52
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Simulated photo-degradation of dissolved organic matter in lakes revealed by three-dimensional excitation-emission matrix with regional integration and parallel factor analysis
摘要： Simulated photo-degradation of fluorescent dissolved organic matter (FDOM) in Lake Baihua (BH) and Lake Hongfeng (HF) was investigated with three-dimensional excitation-emission matrix (3DEEM) fluorescence combined with the fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and multi-order kinetic models. In the FRI analysis, fulvic-like and humic-like materials were the main constituents for both BH-FDOM and HF-FDOM. Four individual components were identified by use of PARAFAC analysis as humic-like components (C1), fulvic-like components (C2), protein-like components (C3) and unidentied components (C4). The maximum 3DEEM fluorescence intensity of PARAFAC components C1eC3 decreased by about 60%, 70% and 90%, respectively after photo-degradation. The multi-order kinetic model was acceptable to represent the photo-degradation of FDOM with correlation coefficient (Radj2) (0.963e0.998). The photo-degradation rate constants (kn) showed differences of three orders of magnitude, from 1.09(cid:1) 10(cid:3)6 to 4.02 (cid:1) 10(cid:3)4 min(cid:3)1, and half-life of multi-order model (Tn1=2) ranged from 5.26 to 64.01 min. The decreased values of fluorescence index (FI) and biogenic index (BI), the fact that of percent fluorescence response parameter of Region I (PI,n) showed the greatest change ratio, followed by percent fluorescence response parameter of Region II (PII,n), while the largest decrease ratio was found for C3 components, and the lowest Tn1=2 was observed for C3, indicated preferential degradation of protein-like materials/components derived from biological sources during photo-degradation. This research on the degradation of FDOM by 3DEEM/FRI-PARAFAC would be beneficial to understanding the photo-degradation of FDOM in natural environments and accurately predicting the environmental behaviors of contaminants in the presence of FDOM.
关键词： Fluorescence regional integration,Parallel factor analysis,Photo-degradation,Fluorescent dissolved organic matter,Multi-order kinetic models,Three-dimensional excitation-emission matrix
更新于2025-09-16 10:30:52
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A Projective Method for the Calculation of Excited State Electronic Coupling: Isolating Charge Transfer/Recombination Processes in Organic Photovoltaics
摘要： Electronic coupling between excited states is a vital parameter required in order to describe the ultrafast energy and charge transfer processes that occur in photo-responsive organic materials. In such systems short-range Coulombic, exchange, overlap, and configuration interaction effects must all be accounted for. Although a number of methods are available, the evaluation of the coupling between arbitrary excited states remains challenging. In this contribution, a flexible and scalable method for the calculation of short-range electronic coupling between excited states is developed. Excitation- or charge-localized states are projected onto the adiabatic states of a dimeric molecular system using an efficient wavefunction overlap algorithm. In addition to correctly treating Coulombic, exchange and overlap interactions, the inclusion of multistate interactions is inherent in the procedure. The method is then used to disentangle excitation energy transfer, charge-transfer, and charge recombination processes in donor acceptor systems relevant to organic photovoltaics, with a view towards the development of material design principles. Calculations were performed within single-excitation frameworks, but the scheme has the potential to be extended to multireference/higher-order excitation quantum-chemical methods.
关键词： excitation energy transfer,excited states,electronic coupling,charge transfer,organic photovoltaics
更新于2025-09-16 10:30:52
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Direct observation of elastic softening immediately after femtosecond-laser excitation in a phase-change material
摘要： The generation and propagation of photoexcited elastic waves in crystalline Ge2Sb2Te5 were analyzed by picosecond time-resolved x-ray diffraction using a femtosecond-laser pump and an x-ray free-electron laser probe technique. The crystalline lattice anisotropically expanded initially in approximately 20 ps after the excitation. This was followed by a periodic oscillation of the lattice strain. The elastic stiffness along the cubic [111] direction had significantly softened during the initial expansion, and the strain magnitude was the largest in the [100] and [110] directions. This indicates that femtosecond-laser excitation creates a shallower interlayer potential between the Te and Ge-Sb layers and eventually leads to softening of the elastic stiffness along the cubic [111] direction. Furthermore, this softened state increases the system’s sensitivity to an external stress field. This residual internal stress in a thin film enhances the selective formation of a particular type of variant during the symmetry change from cubic to rhombohedra. This causes the subsequent anisotropic expansion. These phenomena are quite interesting and align with the ultrafast amorphization of this material.
关键词： elastic stiffness,femtosecond-laser excitation,elastic waves,x-ray diffraction,phase-change material
更新于2025-09-16 10:30:52
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[IEEE 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Zatoka, Ukraine (2018.9.9-2018.9.14)] 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Efficient Two-Photon Luminescence for Bioimaging Using Polymer Conjugations of Graphene Quantum Dots Based Materials
摘要： In this study, examination results revealed that conjugated polymers containing nitrogen and sulfur atoms lead to a higher quantum confinement of emissive energy trapped on the surface of material (graphene quantum dot (GQD)-polymers), resulting in a high luminescence quantum yield and impressive two-photon properties. Additionally, the GQD-polymers generated nonreactive oxygen species-dependent oxidative stress on cells. Furthermore, we demonstrated the effective use of two-photon excitation-mediated high two-photon luminescence intensity in an acidic environment enabled GQD-polymers to act as a promising contrast probe. When cancer cells are labeled with specific antibody GQD-polymers conjugates, molecular-specific imaging can be performed deep into a tissue phantom with extremely high signal-to-noise ratios. In situations in which imaging depths are limited by the maximum available power that can be delivered to the three-dimensional (3D) bioimaging plane without causing damage to tissue, GQD-polymers might provide sufficient brightness to extend the maximum depth of imaging. Moreover, we demonstrated that the use of GQD-polymers can expand the capabilities of two-photon imaging to allow noninvasive 3D bioimaging of a variety of new molecular signatures.
关键词： photostability,reactive oxygen species,three-dimensional bioimaging,photodynamic therapy,two-photon excitation,contrast probe,graphene,quantum dot-polymer,two-photon luminescence,two-photon,contrast agent,nitrogen-doped graphene quantum dots
更新于2025-09-16 10:30:52
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Femtosecond Laser-Induced Electron Emission from Nanodiamond-Coated Tungsten Needle Tips
摘要： We present femtosecond laser-induced electron emission from nanodiamond-coated tungsten tips. Based on the shortness of the femtosecond laser pulses, electrons can be photoexcited for wavelengths from the infrared (1932 nm) to the ultraviolet (235 nm) because multiphoton excitation becomes efficient over the entire spectral range. Depending on the laser wavelength, we find different dominant emission channels identified by the number of photons needed to emit electrons. Based on the band alignment between tungsten and nanodiamond, the relevant emission channels can be identified as specific transitions in diamond and its graphitic boundaries. It is the combination of the character of initial and final states (i.e., bulk or surface-near, direct or indirect excitation in the diamond band structure), the number of photons providing the excitation energy, and the peak intensity of the laser pulses that determines the dominant excitation channel for photoemission. A specific feature of the hydrogen-terminated nanodiamond coating is its negative electron affinity that significantly lowers the work function and enables efficient emission from the conduction band minimum into vacuum without an energy barrier. Emission is stable for bunch charges of up to 400 electrons per laser pulse. We infer a normalized emittance of <0.20 nm rad and a normalized peak brightness of >1.2 × 1012 A m?2 sr?1. The properties of these tips are encouraging for their use as laser-triggered electron sources in applications such as ultrafast electron microscopy as well as diffraction and novel photonics-based laser accelerators.
关键词： nanodiamond,ultrafast electron microscopy,tungsten tips,multiphoton excitation,electron emission,negative electron affinity,femtosecond laser
更新于2025-09-16 10:30:52
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AIP Conference Proceedings [AIP Publishing ADVANCES IN BASIC SCIENCE (ICABS 2019) - Bahal, India (7–9 February 2019)] ADVANCES IN BASIC SCIENCE (ICABS 2019) - Upconversion emission of Ag nanoparticles with Er3+/Yb3+ ions in tellurite glasses under 980nm laser excitation
摘要： The light upconversion in Er3+ - Yb3+ doped TeO2 -WO3- Li2O (TWLEY) doped glass containing silver nanoparticles (NPs) has been reported. Tellurite based glasses have been prepared by melt quenching technique with small amount Ag nanoparticles(NPs). The optical excitation is made at 980 nm in resonance with the 2F5/2→2F7/2 transition of Yb3+ ions in glass system. Intense emission bands centered at 525nm, 550nm, and 654 nm were observed corresponding to Er3+ ions transitions. Upconversion fluorescence Intensity of the glasses samples are also observed at 980nm femtosecond laser excitation using two photons microscope. For this green and red colour intensity measurement of the TWLEY with Ag NPs glass sample has been analyzed by intensity histograms. Results show that plasmon enhances upconversion of silver and rare-earth doped glasses may be utilized to explore its potential for multiphoton microscopy.
关键词： Tellurite glasses,Ag nanoparticles,Er3+/Yb3+ ions,980nm laser excitation,Upconversion emission
更新于2025-09-16 10:30:52