Lifetimes Of Emitters Research Articles

Purcell effect of nitrogen-vacancy centers in nanodiamond coupled to propagating and localized surface plasmons revealed by photon-correlation cathodoluminescence

We measured the second-order correlation function of the cathodoluminescence intensity and investigated the Purcell effect by comparing the lifetimes of quantum emitters with and without metal structure. The increase in the electromagnetic local density of state due to the coupling of a quantum emitter with a plasmonic structure causes a shortening of the emitter lifetime, which is called the Purcell effect. Since the plasmon-enhanced electric field is confined well below the wavelength of light, the quantum emitter lifetime is changed in the nanoscale range. In this study, we combined cathodoluminescence in scanning (transmission) electron microscopy with Hanbury Brown-Twiss interferometry to measure the Purcell effect with nanometer and nanosecond resolutions. We used nitrogen-vacancy centers contained in nanodiamonds as quantum emitters and compared their lifetime in different environments: on a thin SiO2 membrane, on a thick flat silver film, and embedded in a silver film. The lifetime reductions of nitrogen-vacancy centers were clearly observed in the samples with silver. We evaluated the lifetime by analytical calculation and numerical simulations and revealed the Purcell effects of emitters coupled to propagating and localized surface plasmons. This is the first experimental result showing the Purcell effect due to the coupling between nitrogen-vacancy centers in nanodiamonds and surface plasmon polaritons with nanometer resolution.

Three‐ and Four‐Coordinate, Boron‐Based, Thermally Activated Delayed Fluorescent Emitters

AbstractRecent developments in purely organic‐material‐based thermally activated delayed fluorescence (TADF) emitters are helping to make them suitable for commercial applications in the near future. In spite of their high external quantum efficiencies, the broad emission spectra and short device lifetimes are the main barriers to using TADF emitters. Among the classes of materials, boron‐embedded polycyclic aromatic compounds have shown potential as TADF emitters that overcome the technical issues. In particular, highly efficient boron‐based TADF emitters with the advantage of a narrowband emission spectrum have been reported recently relying on the concept of a multi‐resonance effect. Hence, boron TADF emitters have the potential to become next‐generation emitters. Based on the future scope of the boron‐based TADF emitters (especially in development of blue TADF emitters), three‐ and four‐coordinate boron TADF emitters are reviewed. Additionally, future prospects of boron‐based TADF emitters are discussed to resolve the issues of low efficiency and short lifetimes of blue emitters.

Polarized Single-Particle Quantum Dot Emitters through Programmable Cluster Assembly.

Although fluorescence and lifetimes of nanoscale emitters can be manipulated by plasmonic materials, it is harder to control polarization due to strict requirements on emitter environments. An ability to engineer 3D nanoarchitectures with nanoscale precision is needed for controlled polarization of nanoscale emitters. Here, we show that prescribed 3D heterocluster architectures with polarized emission can be successfully assembled from nanoscale fluorescent emitters and metallic nanoparticles using DNA-based self-assembly methods. An octahedral DNA origami frame serves as a programmable scaffold for heterogeneous nanoparticle assembly into prescribed clusters. Internal space and external connections of the frames are programmed to coordinate spherical quantum dots (QDs) and gold nanoparticles (AuNPs) into heterocluster architectures through site-specific DNA encodings. We demonstrate and characterize assembly of these architectures using in situ and ex situ structural methods. These cluster nanodevices exhibit polarized light emission with a plasmon-induced dipole along the QD-AuNP nanocluster axis, as observed by single-cluster optical probing. Moreover, emittance properties can be tuned via cluster design. Through a systematic study, we analyzed and established the correlation between cluster architecture, cluster orientation, and polarized emission at a single-emitter level. Excellent correspondence between the optical behavior of these clusters and theoretical predictions was observed. This approach provides the basis for rational creation of single-emitter 3D nanodevices with controllable polarization output using a highly customizable DNA assembly platform.

Time-resolved FRET in AgInS2/ZnS-CdSe/ZnS quantum dot systems

The fast and accurate detection of disease-related biomarkers and potentially harmful analytes in different matrices is one of the main challenges in the life sciences. In order to achieve high signal-to-background ratios with frequently used photoluminescence techniques, luminescent reporters are required that are either excitable in the first diagnostic window or reveal luminescence lifetimes exceeding that of autofluorescent matrix components. Here, we demonstrate a reporter concept relying on broad band emissive ternary quantum dots (QDs) with luminescence lifetimes of a few hundred nanoseconds utilized for prolongating the lifetimes of organic or inorganic emitters with lifetimes in the order of a very few 10 ns or less through fluorescence resonant energy transfer. Using spectrally resolved and time-resolved measurements of the system optical response we demonstrate the potential of lifetime multiplexing with such systems exemplarily for AgInS2/ZnS and CdSe/ZnS QDs.

Probing Plasmon-NV0 Coupling at the Nanometer Scale with Photons and Fast Electrons

The local density of optical states governs an emitters lifetime and quantum yield through the Purcell effect. It can be modified by a surface plasmon electromagnetic field, but such a field has a spatial extension limited to a few hundreds of nanometers, which complicates the use of optical methods to spatially probe the emitter-plasmon coupling. Here we show that a combination of electron-based imaging, spectroscopies and photon-based correlation spectroscopy enables measurement of the Purcell effect with nanometer and nanosecond spatio-temporal resolutions. Due to the large variability of radiative lifetimes of emitters embedded in nanoparticles with inhomogeneous sizes we relied on a statistical approach to unambiguously probe the coupling between nitrogen-vacancy centers (NV^0) in nanodiamonds and surface plasmons in silver nanocubes. We quantified the Purcell effect by measuring the NV^0 excited state lifetimes in a large number of either isolated nanodiamonds or nanodiamond-nanocube dimers and demonstrated a statistically significant lifetime reduction for dimers.

Lifetime extension of in-core self-powered neutron detector using new emitter materials

Summary In this paper, new in-core self-powered neutron detector emitter candidate materials, ie, vanadium, cobalt, and silver, have been examined in their lifetimes compared with the commonly used rhodium emitter. Using a new quantitative lifetime evaluation model, the lifetimes of vanadium and cobalt were determined to be longer than that of rhodium, but these materials were also shown to have the disadvantage of low signal intensities. Under normal operating conditions, we showed that rhodium emitter can be used for 2 cycles of pressurized water reactors (PWRs) with lifetime of 4.35 years, whereas silver can be used for 5 cycles of PWRs with lifetime of 8.04 years. Three sensitivity tests were performed for rhodium and silver about (1) the emitter size, (2) the fuel assembly burnup, and (3) the emitter temperature variations. From the test results, we observed that the lifetimes of rhodium and silver emitters remained 2 and 5 cycles long, respectively. We concluded that silver can significantly extend the in-core detector's lifetime in PWR operation.

Field evaporation behaviour for carbon nanotube thin-film

In recent years, the carbon nanotube (CNT) emitters used for ion sources or gas sensors have been investigated, and the progress of several approaches such as field ionization and field desorption sources has been reported. However, a major concern for these applications is possible loss of CNTs caused by field evaporation, which can shorten the lifetimes of CNT-based emitters used for high electric field ion sources. So in CNT-based field emitter technology, emitter lifetime and degradation will be key parameters to be controlled. However, up to now only very few investigations in this direction have been conducted. The reason for this might lie in the fact that one often considers that the threshold value of field evaporation for a kind of material ( 40 V/nm) is much higher than the field of ionization or desorption ( 10 V/nm) according to the metal material characteristics (such as the threshold values of field evaporation for tungsten and molybdenum are 54 V/nm and 45 V/nm, respectively). In this work, the carbon nanotube thin-film (the density of CNTs is about 2.5108/cm2) is fabricated by screen-printing method, and the field evaporation behavior of CNT thin-film is studied experimentally in an ultrahigh vacuum system typically operating at a pressure of lower than 10-9 Torr after a 4-hour bake-out at ~200℃. Unlike the vertically aligned CNT array having higher electric field around the edge of the array because of the shielding effect, the printed CNT thin-film has more uniform distribution of electric field and is very easy to relize the mass production. The results show that the prepared CNT thin-film has quite obvious field evaporation behavior (some contaminants have deposited on the surface of grid after field evaporation, and energy-dispersive X-ray spectroscopy elemental mapping result of the grid indicates that the contaminants consist mainly of carbon elements), with turn-on field in a range of 10.0-12.6 V/nm, ion current could reach up to hundreds of pA. Meanwhile, the results with scanning electron microscope analysis and field electron emission measurement indicate that the CNT distribution turns into more non-uniform distribution after field evaporation; even some CNTs are directly dragged away from the substrate by the strong field. The field evaporation of CNT thin-film also leads to field electron emission onset voltage increasing from 240 V to 300 V, field enhancement factor decreasing from 8300 to 4200, and threshold field of field evaporation rising from 10.0 V/nm to 12.6 V/nm. However, the repeatability of sample treated by the field evaporation brings about an improvement to a certain extent. It could be understood in this way: upon applying a positive voltage, the most protruding parts, which have the strongest emissive capability, are evaporated first, which leads to the declined field enhancement factor; the parts of CNTs which have relatively weak emissive capability are not evaporated. So the uniformity of electric field is improved through reducing the difference in field enhancement factor rather than surface morphology between carbon nanotubes. The field evaporation of CNT thin-film is also a process which improves the uniformity of electric field. Therefore, the stability and repeatability of the field electron emission for carbon nanotube thin-film are improved naturally.

Proposal for a room-temperature diamond maser.

The application of masers is limited by its demanding working conditions (high vacuum or low temperature). A room-temperature solid-state maser is highly desirable, but the lifetimes of emitters (electron spins) in solids at room temperature are usually too short (∼ns) for population inversion. Masing from pentacene spins in p-terphenyl crystals, which have a long spin lifetime (∼0.1 ms), has been demonstrated. This maser, however, operates only in the pulsed mode. Here we propose a room-temperature maser based on nitrogen-vacancy centres in diamond, which features the longest known solid-state spin lifetime (∼5 ms) at room temperature, high optical pumping efficiency (∼106 s−1) and material stability. Our numerical simulation demonstrates that a maser with a coherence time of approximately minutes is feasible under readily accessible conditions (cavity Q-factor ∼5 × 104, diamond size ∼3 × 3 × 0.5 mm3 and pump power <10 W). A room-temperature diamond maser may facilitate a broad range of microwave technologies.

Metallodielectric Hybrid Antennas for Ultrastrong Enhancement of Spontaneous Emission

We devise new optical antennas that reduce the excited-state radiative lifetimes of emitters to the order of 100fs while maintaining quantum efficiencies of about 80% at a broadband operation. Here, we combine metallic nanoparticles with planar dielectric structures and exploit design strategies from plasmonic nanoantennas and concepts from cavity quantum electrodynamics to maximize the local density of states and minimize the nonradiative losses incurred by the metallic constituents. The proposed metallodielectric hybrid antennas promise an important impact on various fundamental and applied research fields, including photophysics, ultrafast plasmonics, bright single-photon sources, and Raman spectroscopy.

Half-lives of proton emitters using relativistic mean field theory

The proton radioactivity lifetimes of proton emitters from the ground and the isomeric states are calculated using the microscopic M3Y $+$ Ex and R3Y $+$ Ex (proposed) nucleon-nucleus interaction potentials. These interaction potentials are obtained by single folding the densities of the daughter nuclei supplemented by a zero-range pseudopotential. The quantum-mechanical-tunneling probability is calculated within the WKB approximation. The calculated results are found to be in good agreement with the experimental data for both the M3Y and R3Y interactions.

Shaking optical nanocavities

Surface acoustic waves can actively modulate the optical mode of a photonic crystal defect cavity. Fast tuning rates, compared with the typical lifetimes of optical emitters and photons inside the cavity, pave the way for deeper insights into cavity quantum electrodynamics.

Lifetime distribution of spontaneous emission from emitter(s) in three-dimensional woodpile photonic crystals

Spontaneous emission lifetime distribution in the basic unit cell or on a plane of the excited emitters embedded in woodpile photonics crystals with low refractive index contrast are investigated. It is found that the spontaneous emission lifetime distribution strongly depends on the position and transition frequency of the emitters, and has the same symmetry as that of the unit cell. The lifetimes of emitters near the upper gap edge are longer than that in the center of the pseudo-gap, which is quite a contrast to the conventional concept. Furthermore, it is revealed that the polarization orientation of the emitters has significant influence on the lifetime distribution, and may result in a high anisotropy factor (defined as the difference between the maximum and minimum values of the lifetime) up to 4.2. These results may be supplied in probing the lifetime distribution or orientation-dependent local density of states in future experiments.

Two-proton radioactivity and three-body decay. II. Exploratory studies of lifetimes and correlations

Theoretical studies of prospective $2p$ emitters are performed in a three-body $\text{core}+p+p$ model. Lifetime dependencies on the decay energy are calculated for $^{45}\mathrm{Fe}$, $^{48}\mathrm{Ni}$, $^{54}\mathrm{Zn}$, $^{58}\mathrm{Ge}$, $^{62}\mathrm{Se}$, $^{66}\mathrm{Kr}$, and compared to the quasiclassical estimates. The observation of products from the in-flight decays is discussed as an important technique supplementing a standard implantation method for a broad range of lifetimes of prospective two-proton emitters. The sensitivity of the model to various aspects of nuclear dynamics is demonstrated on the $^{45}\mathrm{Fe}$ example. Possible momentum correlations for emitted protons are discussed with the emphasis on $^{19}\mathrm{Mg}$ and $^{45}\mathrm{Fe}$. We study convergence and stability of theoretical momentum distributions with respect to different physical and numerical aspects of the model. Opportunities to extract valuable information on $2p$ emission from incomplete kinematics decay data are discussed.

Extending lifetimes of lanthanide-based near-infrared emitters (Nd, Yb) in the millisecond range through Cr(III) sensitization in discrete bimetallic edifices.

A [Cr(alpha,alpha'-diimine)3]3+ chromophore is used as a donor for sensitizing NdIII and YbIII near-infrared (NIR) emitters in the heterobimetallic helicates [LnCrIIIL3]6+. The intramolecular CrIII --> LnIII energy transfer process controls the population of the lanthanide-centered emitting levels, thus leading to unprecedented extension of the NIR luminescence decay times in the millisecond range for Nd and Yb ions incorporated in coordination complexes.

Fluorescence lifetimes of molecular dye ensembles near interfaces

Fluorescence lifetimes of thin, rhodamine 6G-doped polymer layers in front of a mirror have been determined as a function of the emitter-mirror separation and the conditions of excitation and observation. Lifetime is well known to depend on the spatial emitter-mirror separation. The explanation of experimental data needs to consider direction, polarization, and numerical aperture of the experimental system. As predicted theoretically, experimental results depend on the conditions of illumination and observation, because of the different lifetimes of emitters aligned horizontally or vertically with respect to the plane of interfaces and their selection by the experimental system. This effect is not observable when ions are used as a source of fluorescence, because ensemble averaging depends on the properties of sources.

Spontaneous emission of europium ions embedded in dielectric nanospheres.

We measure fluorescence lifetimes of emitters embedded in isolated single dielectric nanospheres. By varying the diameters of the spheres from 100 nm to 2 microm and by modifying their dielectric surrounding, we demonstrate a systematic change of paradigm in the spontaneous emission rate, as we cross the border from the superwavelength regime of Mie resonances to the nanoscopic realm of Rayleigh scattering. Our data show inhibition of the spontaneous emission up to 3 times and are in excellent agreement with the results of analytical calculations.

Vacuum-UV fluorescence spectroscopy of BF3 and BCl3 in the range 9-22 eV: dispersed spectra and radiative lifetimes

The fluorescence processes following vacuum-UV (VUV) photoexcitation of BF3 and BCl3 in the energy range 9-22 eV have been studied using synchrotron radiation from the BESSY 1, Berlin source. The fluorescence is dispersed in a secondary monochromator, whereby information on the nature of the emitting species is obtained. For excitation energies in the range 13-17 eV, photodissociation of Rydberg states of BF3 produces a substantial branching ratio into two, possibly three, excited valence states of the BF2 free radical, which fluoresce to the ground state. The dispersed spectra are compared with predictions from ab initio calculations of the electronic spectroscopy of this radical. Fluorescence from BCl3 photoexcited in the range 9-22 eV is more complicated, with emissions having already been observed and mostly assigned in BCl2, BCl, BCl3+, BCl2+ and B. Using the single-bunch, pulsed mode of the BESSY 1 source, the radiative lifetimes of emitters from BCl3 lying in the range 3-100 ns have been measured. Our results for BCl3 are compared with data from other techniques. Where more than one emitter is excited at a particular VUV energy, the dispersion of the induced fluorescence through a monochromator means that the lifetimes of the different emitters can be differentiated.

Vacuum-UV fluorescence spectroscopy of PF3 in the range 9–20 eV

The vacuum-UV and visible spectroscopy of PF3 using fluorescence excitation and dispersed emission techniques is reported. The fluorescence excitation spectrum has been recorded following photoexcitation with monochromatized synchrotron radiation from the Daresbury, UK source in the energy range 9–20 eV with an average resolution of ∼0.015 eV. Transitions to the three lowest-energy bands in the Rydberg spectra show resolved vibrational structure, they are assigned to transitions to the (8a1)−1 4p, 5p, and 6p Rydberg states of PF3, and fluorescence is due to valence transitions in the PF2 radical. From a Franck–Condon analysis of the vibrational structure, it is shown that the FPF bond angle in PF3 increases by ∼14±1° upon photoexcitation. The use of optical filters shows that at least three excited electronic states of PF2 are responsible for the induced emission. Dispersed emission spectra in the UV/visible region have been recorded with an optical resolution of 8 nm at the BESSY 1, Germany synchrotron source at the energies of all the peaks in the excitation spectrum. Four different decay channels are observed: (a) PF2 à 2A1–X̃ 2B1 fluorescence in the wide range 320–550 nm for photon energies around 9.8 eV, (b) PF2 ÖX̃, and B̃ 2B2–X̃ 2B1 fluorescence at ∼300 nm for photon energies around 11.0 eV, (c) PF2 C̃ 2A1–X̃ 2B1 and Ẽ 2B1 (2Π)–à 2A1 fluorescence at ∼222 and 325 nm, respectively, for photon energies around 14.4 eV, and (d) PF A 3Π–X 3Σ− fluorescence between 300–380 nm for photon energies around 16.1 eV. These assignments are confirmed by action spectra in which the excitation energy of the vacuum-UV radiation is scanned with detection of the fluorescence at a fixed, dispersive wavelength. Using the single-bunch mode of the BESSY 1 source, we have attempted to measure the lifetimes of the emitting states, but the timing profile of the source imposes an upper limit on lifetimes that can be measured of ∼500 ns. We have therefore only been able to measure values for the bent C̃ 2A1 and linear Ẽ 2B1 (2Π) states of PF2 of 14.7 and 7.9 ns, respectively; the lifetimes of the other emitters are too long to measure by this method. Our assignments in PF2 are heavily dependent on recent ab initio calculations on the geometries and energies of the valence electronic states of this species. Our knowledge on the electronic spectroscopy of this free radical is reviewed.

Effect of guest-host interaction on spectra and relaxation dynamics of matrix-isolated Br 2 B 3Π 0 + u , A 3Π 1u, and A′ 3Π 2u

Time-resolved fluorescence spectra of matrix-isolated isotopically pure Br 2 in argon have been obtained in the range 600–1700 nm, using pulsed laser excitation at 500 nm. The vibrational assignment of the BX progression is in conflict with previous work, while published tentative assignments of the AX and A′X progression have been confirmed. The RKR potential of matrix-isolated Br 2 X 1Σ + g is found to be wider than in the gas phase. The Franck—Condon distributions of the observed progressions deviate significantly from the respective gas phase distributions. Theoretical Franck—Condon distributions could be fitted to the observed ones by increasing the equilibrium internuclear separations in the excited states, relative to the electronic ground state. The matrix effects could be qualitatively reproduced by adding a sum of Lennard-Jones pair potentials to the Morse potentials. The B X, A X, and A′ X progressions contribute 0.085%, 2.3% and 97.6% to the fluorescence intensity in argon, indicating effective vibronic relaxation of the absorbing states. The A-state fluorescence consists of two spectrally resolvable components with different lifetimes. The lifetimes of the matrix-isolated emitters are: B 3Π 0 + u , 6.57±0.05 μs; A 3Π 1u, 61±1 and 107±7 μs; and A′ 3Π 2u, 44.2±3 ms.

Lifetimes of metastable X-ray emitters in helium- and lithium-like chlorine

We have used coincidence techniques to identify the charge states of metastable K X-ray emitters produced in foil excitation of energetic chlorine beams. At 55 MeV the emitting states are found to belong primarily to helium- and lithium-like chlorine ions. Charge-state separated decay curves for these ionic species are characterized by lifetimes of 2.2±0.3 ns and 0.95±0.2 ns for two- and three-electron systems respectively. The corresponding emitting states are thought to be the (1s2p) 3P 2 0 and ( s2 s2 p) 4 P 5 2 0 levels in helium- and lithium-like chlorine respectively, both of which may radiatively decay by M2 photon emission.