The intensities of vibronic lines are experimentally measured in fluorescence and fluorescence excitation spectra of jet-cooled anthracene. An original method is developed for calculating geometrical parameters of benzene hydrocarbons in the ground and excited electronic states. Using these parameters, the intensities of vibronic lines in fluorescence and absorption spectra of anthracene are calculated in the Franck-Condon approximation taking into account the mixing of all the twelve normal coordinates of totally symmetric vibrational modes. After correction for the quantum yield of fluorescence, good agreement is obtained between the calculated line intensities in the absorption spectrum and the measured line intensities in the fluorescence excitation spectrum. Based on these data, a new assignment of the lines in the fluorescence excitation spectrum corresponding to totally symmetric modes 7 and 8 is suggested. 相似文献
Abstract The fluorescence of anthracene vapors and its derivatives initiated by triplet-triplet excitation is observed. The quantum yield of inverce intersystem crossing of anthracene molecules is estimated (10?2). The fluorescence initiated by triplet excitation is quenched by foreign pentane gas, thus permitting an estimation of the lifetime of highly excited triplet molecules. 相似文献
We used the Jordan–Wigner transform and the invariant eigenoperator method to study the magnetic phase diagram and the magnetization curve of the spin-1/2 alternating ferrimagnetic diamond chain in an external magnetic field at finite temperature. The magnetization versus external magnetic field curve exhibits a 1/3 magnetization plateau at absolute zero and finite temperatures, and the width of the 1/3 magnetization plateau was modulated by tuning the temperature and the exchange interactions. Three critical magnetic field intensities H_(CB), H_(CE) and H_(CS) were obtained, in which the H_(CB) and H_(CE) correspond to the appearance and disappearance of the 1/3 magnetization plateau, respectively, and the higher H_(CS) correspond to the appearance of fully polarized magnetization plateau of the system. The energies of elementary excitation ωσ,k(σ = 1, 2, 3) present the extrema of zero at the three critical magnetic fields at 0 K, i.e., [hω_(3,k)(HCB)]_(min)= 0, [hω_(2,k)(H_(CE))]_(max)= 0 and [hω _(2,k)(H_(CS))]_(min)= 0, and the magnetic phase diagram of magnetic field versus different exchange interactions at 0 K was established by the above relationships. According to the relationships between the system's magnetization curve at finite temperatures and the critical magnetic field intensities, the magnetic field-temperature phase diagram was drawn. It was observed that if the magnetic phase diagram shows a three-phase critical point, which is intersected by the ferrimagnetic phase, the ferrimagnetic plateau phase, and the Luttinger liquid phase, the disappearance of the1/3 magnetization plateau would inevitably occur. However, the 1/3 magnetization plateau would not disappear without the three-phase critical point. The appearance of the 1/3 magnetization plateau in the low temperature region is the macroscopic manifestations of quantum effect. 相似文献
Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications. 相似文献
Spectroscopic characteristics, i.e. absorption, fluorescence, fluorescence excitation spectra, fluorescence decay time, fluorescence polarization degree of novel silicon-containing organic polymers including main chain anthracene groups were investigated. Three kinds of emission spectra were revealed and assigned to polaron–exciton, anthracene and anthracene dimer. The measured fluorescence polarization spectra gave evidence of directed excitation energy migration along the disordered polymeric chain. Strong quenching of anthracene fluorescence during the polaron–exciton lifetime was interpreted as a result of the interaction between two excitations that causes anthracene anion-radical formation. The third-order nonlinear susceptibility of the polymers in solution measured by the Z-scan technique at 1054 nm is 190×10−14 cm2 W−1. 相似文献
We report that,by linearly polarized pumping of different wavelengths,Kerr transients appear at zero magnetic field only in the case when GaMnAs samples are initialized at 3 K by first applying a 0.8 Tesla field and then returning to zero field.We find that,instead of magnetization precession,the near-band gap excitation induces a coherent out-of-plane turning of magnetization,which shows very long relaxation dynamics with no precession.When photon energy increases,the peak value of the Kerr transient incre... 相似文献
The TbNi5 compound shows an interesting magnetic phase transition with an incommensurate structure below 23 K, whose true nature remains unresolved. In order to solve this question, we have carried out polarized neutron diffraction experiments by measuring temperature and field dependence of the intensities of satellites and Bragg reflections. From the temperature dependence of both satellite peaks and Bragg reflection, we demonstrated that it has only one magnetic structure at a given temperature. Furthermore, unlike previous reports, we found that both ferromagnetic and modulated components of the Tb ion magnetic moments should be collinear to each other. Our data also show strong depolarisation effects that are most likely to arise from domain structure of ferromagnetic component. A critical field, which destroyers a modulated magnetic structure is found to be lower than a field value to saturate the ferromagnetic component, in which the intensity of Bragg ferromagnetic reflections reaches saturation. 相似文献
Coherent electronic dynamics are of great significance in photo-induced processes and molecular magnetism. We theoretically investigate electronic dynamics of triatomic molecule H32+ by circularly polarized pulses, including electron density distributions, induced electronic currents, and ultrafast magnetic field generation. By comparing the results of the coherent resonant excitation and direct ionization, we found that for the coherent resonant excitation, the electron is localized and the coherent electron wave packet moves periodically between three protons, which can be attributed to the coherent superposition of the ground A' state and excited E+ state. Whereas, for the direct single-photon ionization, the induced electronic currents mainly come from the free electron in the continuum state. It is found that there are differences in the intensity, phase, and frequency of the induced current and the generated magnetic field. The scheme allows one to control the induced electronic current and the ultrafast magnetic field generation. 相似文献
Metasurfaces, which consist of resonant metamaterial elements in the form of two‐dimensional thin planar structures, retain great capabilities in manipulating electromagnetic wave and potential applications in modifying interaction with fluorescent molecules. The metasurfaces with magnetic responses are favorable to weakening fluorescence quenching while less investigated in controlling fluorescence. In this paper, we demonstrate control over fluorescence emission by engineering the magnetic and electric modes in plasmonic metasurfaces consisting of 45‐nm‐thick gold split‐ring‐resonators (SRRs). The fluorescence emission exhibits an enhancement factor of ∼18 and is predominantly x‐polarized with assistance of the magnetic mode excited by oblique incidence with an x‐polarized electric field. The magnetic and electric modes excited by oblique incidence with a y‐polarized electric field contribute to the rotation of emission polarization with respect to the incident polarization. The results demonstrate manipulating the interaction of fluorescent emitters with different resonant modes of the SRR‐based metasurface at the nanoscale by the polarization of incident light, providing potential applications of metasurfaces in a wide variety of areas, including optical nanosources, fluorescence spectroscopy and compact biosensors.
Organic dye particles of micrometer and submicrometer diameters were prepared by a wetting/dewetting procedure on a hydrophilic glass surface and a self-organized one- or two-dimensional registration was observed. To analyze the molecular assembly in these particles the near-field-excited near-field fluorescence from single particles were detected, while the majority of particles with diameters around 2 μm or less did not show fluorescence. Far-field fluorescence, in contrast, was observed for every particle, and the intensity depended on the excitation polarization when a polarized evanescent field was used for excitation, indicating that the molecules’ transition moment within dye particles orient parallel to the substrate surface. These two observations suggest that the near-field at the tip of the probe was polarized parallel to the probe axis. Another observation, that neighboring particles show similar molecular orientations, suggests that the dewetting process contributed to the alignment of the molecular directions in adjacent particles, which further proves that the dye particles were formed by a self-organizing mechanism. 相似文献
Microbubbles loaded with magnetic nanoparticles (MMBs) have attracted increasing interests in multimode imaging and drug/gene delivery and targeted therapy. However, the dynamic behaviors generated in diagnostic and therapeutic applications are not clear. In the present work, a novel theoretical model of a single MMB was developed, and the dynamic responses in an infinite viscous fluid were investigated under simultaneous exposure to magnetic and acoustic fields. The results showed that the amplitude reduces and the resonant frequency increases with the strength of the applied steady magnetic field and the susceptibility of the magnetic shell. However, the magnetic field has a limited influence on the oscillating. It is also noticed that the responses of MMB to a time-varying magnetic field is different from a steady magnetic field. The subharmonic components increase firstly and then decrease with the frequency of the magnetic field and the enhanced effect is related to the acoustic driving frequency. It is indicated that there may be a coupling interaction effect between the acoustic and magnetic fields. 相似文献
Investigations of the optical isotropic plastic scintillator showed that the fluorescence light is more polarized perpendicular than parallel to the particle impact direction. Furtheron the fluorescence light polarization of anthracene crystals proved to be dependent on particle impact direction. Both the degree of fluorescence light polarization of plastic scintillator and the dependence of fluorescence light polarization of anthracene crystals could be explained by the mechanism of energy travelling from direct excited to light emitting molecules. 相似文献
Two novel stilbene derivatives bearing anthracene core based on 1,3,4-oxadiazole were efficiently synthesized and characterized by 1H-NMR, mass spectrometry and elemental analysis. The optical properties of the title compounds were investigated by UV–vis absorption and fluorescence emission spectra in different solvents. Chemical calculations were performed by density functional theory (DFT) at the (B3LYP)/6-31G* level. The results show the two compounds exhibit strong green fluorescence emission ranged from 489–493 nm, and the fluorescence quantum yield ranged from 0.78–0.92. Their HOMO and LUMO levels are (?5.44 eV, ?2.25 eV) and (?5.45 eV, ?2.28 eV), respectively. The influence of the solvent on the fluorescence intensities was also discussed. 相似文献