Measurement of the radiative and nonradiative decay rates of single CdSe nanocrystals through a controlled modification of their spontaneous emission

We present a simple method to measure the radiative and nonradiative recombination rates of individual fluorescent emitters at room temperature. By placing a single molecule successively close and far from a dielectric interface and simultaneously measuring its photoluminescence decay and its orientation, both the radiative and nonradiative recombination rates can be determined. For CdSe nanocrystals, our results demonstrate that the fluorescence quantum efficiency, determined at the single-molecule level, is 98% in average, far above the value expected from conventional ensemble experiments. The bidimensional nature of the transition dipole is also directly evidenced from a single-particle measurement.     

Radiative and nonradiative decay rates in chromium-related centers in nanodiamonds

We address for the first time the measurement of nonradiative decay rates in Cr-related centers in nanodiamonds. Compared to our previous quantum efficiency measurement of Cr centers created in bulk diamond, separate measurements of radiative and nonradiative decay rates in grown nanodiamonds prove more challenging due to size dependence effects. We demonstrate in this Letter that, using defocused dipole imaging and collection efficiency calculation via finite-difference time-domain (FDTD), a quantum efficiency up to 0.9 can be inferred to Cr-related centers showing a 2-level system photon statistics.     

Fluorescence characteristics of a molecule in the vicinity of a plasmonic nanomatryoska: Nonlocal optical effects

The fluorescence characteristics of a dipole molecule in the vicinity of a spherical multilayered metallic nanoshell (a plasmonic nanomatryoska) of ultra-small dimensions is studied via electrodynamic modeling, where we have computed the fluorescence decay rates, the shifts in emission frequency, and the overall fluorescence yields for molecular dipoles of both tangential and radial orientations. Our focus is on structures of ultra small dimensions in order to elucidate the possibly novel nonlocal optical effects in such a phenomenon. The results show that at very close distances between the molecule and the nanoshell, the nonlocal effects in general lead to smaller structure-induced effects with broadened and blue-shifted plasmonic resonances. These effects include overall smaller induced decay rates, smaller red-shifts in emission frequency, and somewhat larger fluorescence yields at low emission frequencies. Physical interpretation of our simulation results is provided.     

Control of single emitter radiation by polarization- and position-dependent activation of dark antenna modes

We study the modification of the decay rates of a single dipolar emitter positioned in the vicinity of metallic linear nanoantennas when higher-order plasmonic excitations are induced. We show that it is possible to effectively tune the enhancement or suppression of both the radiative and nonradiative decay processes by controlling the position and orientation of the dipole with respect to the antenna. Transverse polarization of a single emitter, with respect to the antenna axis, located at the center of the antenna activates dark antenna modes that modify dramatically both the intensity and the spectral features of the decay rates.     

Radiative and nonradiative spontaneous decay rates for an electric quadrupole source in the vicinity of a spherical particle

Analytic expressions for the radiative and nonradiative decay rates for an electric quadrupole source (atom, molecule) in the vicinity of a spherical particle (dielectric, metal) have been derived and analyzed within the classical electrodynamics. It has been shown that the highest increase in the decay rates appears in the quasi-static case, when the wavelength of the transition in question is much larger than the characteristic size of the system formed by the particle and the quadrupole. Asymptotic expressions for the decay rates have been derived for this case.     

硼玻璃中Dy3+及Sm3+的辐射跃迁几率和无辐射跃迁几率

硼玻璃中掺杂Nd3+,Er3+,Tm3+等小能隙的稀土离子,由于硼玻璃声子能量大,多声子无辐射几率大,影响其发光效率。但由于硼玻璃熔点低,加工容易,对于民用上常用的Sm3+,Dy3+,Eu3+,Tb3+等大能隙物质,多声子无辐射跃迁不是主要因素的情况下,发光效率将如何是本文要研究的问题。另外,辐射跃迁性质的研究对于能量传递机理的研究也是很有意义的。     

Role of the Radiation‐Reaction Electric Field in the Optical Response of Two‐Dimensional Crystals

A classical theory of a radiating two‐dimensional crystal is proposed and an expression for the radiation‐reaction electric field is derived. This field plays an essential role in connecting the microscopic electromagnetic fields acting on each dipole of the crystal to the macroscopic one, via the boundary conditions for the system. The expression of the radiative‐reaction electric field coincides with the macroscopic electric field radiating from the crystal and, summed to the incident electric field, generates the total macroscopic electric field.     

Effect of coupled channel mixing on magnetic dipole transitions of charmonium

The effect of coupled channel mixing is included in the calculation of magnetic dipole(M1) one photon radiative decay rates of charmonium by using a nonsingular potential model. We find that the coupled channel mixing has a moderate effect on the M1 decay rates and the calculated decay rates are in better agreement with the experimental data than those predicted by neglecting the effect of coupled channel mixing     

Radiative and non-radiative decay of a single molecule close to a metallic nanoparticle

We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the aim to clarify the distance dependence of the radiative and non-radiative decay rates. We derive analytical formulas based on a dipole-dipole model, and show that the non-radiative decay rate follows a R⁻⁶ dependence at short distance, where R is the distance between the emitter and the center of the nanoparticle, as in Förster’s energy transfer. The distance dependence of the radiative decay rate is more subtle. It is chiefly dominated by a R⁻³ dependence, a R⁻⁶ dependence being visible at plasmon resonance. The latter is a consequence of radiative damping in the effective dipole polarizability of the nanoparticle. The different distance behavior of the radiative and non-radiative decay rates implies that the apparent quantum yield always vanishes at short distance. Moreover, non-radiative decay is strongly enhanced when the emitter radiates at the plasmon-resonance frequency of the nanoparticle.     

Fluorescence quenching of dye molecules near gold nanoparticles: radiative and nonradiative effects

The radiative and nonradiative decay rates of lissamine dye molecules, chemically attached to differently sized gold nanoparticles, are investigated by means of time-resolved fluorescence experiments. A pronounced fluorescence quenching is observed already for the smallest nanoparticles of 1 nm radius. The quenching is caused not only by an increased nonradiative rate but, equally important, by a drastic decrease in the dye's radiative rate. Assuming resonant energy transfer to be responsible for the nonradiative decay channel, we compare our experimental findings with theoretical results derived from the Gersten-Nitzan model.     

Acoustic signature of a submarine hull under harmonic excitation

The structural and acoustic responses of a submarine under harmonic force excitation are presented. The submarine hull is modelled as a cylindrical shell with internal bulkheads and ring stiffeners. The cylindrical shell is closed by truncated conical shells, which in turn are closed at each end using circular plates. The entire structure is submerged in a heavy fluid medium. The structural responses of the submerged vessel are calculated by solving the cylindrical shell equations of motion using a wave approach and the conical shell equations with a power series solution. The far-field radiated sound pressure is then calculated by means of the Helmholtz integral. The contribution of the conical end closures on the radiated sound pressure for the lowest circumferential mode numbers is clearly observed. Results from the analytical model are compared with computational results from a fully coupled finite element/boundary element model.     

Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap

We present time-resolved emission experiments of semiconductor quantum dots in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study is made of crystals with a range of pore radii to tune the band gap relative to the emission frequency. The decay rates averaged over all dipole orientations are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2× outside the gap, in agreement with theory. We discuss the effects of spatial inhomogeneity, nonradiative decay, and transition dipole orientations on the observed inhibition in the band gap.     

Probabilities for radiative vacancy transfer from Li (i=1, 2, 3) sub-shells to the M, N and higher shells for elements with 77≤Z≤92

The probabilities for transfer of the L_i (i=1, 2, 3) subshell vacancy to the M, N and higher shells through radiative decay, ηLiJ(R), have been deduced for the elements with 77≤Z≤92 using the measured L X-ray production cross-sections at (i) the 59.54 keV γ-rays such that BL₁<Einc<BK and (ii) the K X-rays of a suitable secondary target chosen such that BL₃<EKα<BL₂ and BL₁/L₂<EKβ<BK; where BK/Li is the K shell/L_i subshell ionisation threshold of the target element. The deduced probabilities are compared with those calculated using the radiative and nonradiative transition rates based on the Dirac-Fock (DF) and the relativistic Dirac-Hartree-Slater (RDHS) calculations, respectively.     

Sound radiation from point-driven shell structures

A numerical study is presented showing the structural response and sound radiation from a range of thin shell structures excited by a point force: a baffled flat plate, a sphere, a family of spheroids and a family of closed circular cylinders. All the structures have the same material properties, thickness and total surface area so the asymptotic modal density is the same. Dramatic differences are shown in the total radiated sound power for the different shells. It was already known that the flat plate and the sphere behave very differently. These results show that the cylinders and, particularly, the spheroids show patterns that are not intermediate between the two but instead display new features: in certain frequency ranges the radiated sound power can be at least an order of magnitude greater than either the plate or the sphere.     

Nonradiative and radiative Förster energy transfer between quantum dots

We theoretically study nonradiative and radiative energy transfer between two localized quantum emitters, a donor (initially excited) and an acceptor (receiving the excitation). The rates of nonradiative and radiative processes are calculated depending on the spatial and spectral separation between the donor and acceptor states and for different donor and acceptor lifetimes for typical parameters of semiconductor quantum dots. We find that the donor lifetime can be significantly modified only due to the nonradiative Förster energy transfer process at donor–acceptor separations of approximately 10 nm (depending on the acceptor radiative lifetime) and for the energy detuning not larger than 1–2 meV. The efficiency of the nonradiative Förster energy transfer process under these conditions is close to unity and decreases rapidly with an increase in the donor–acceptor distance or energy detuning. At large donor–acceptor separations greater than 40 nm, the radiative corrections to the donor lifetime are comparable with nonradiative ones but are relatively weak.     

Non-radiative decay of a dipole emitter close to a metallic nanoparticle: Importance of higher-order multipole contributions

The contribution of higher-order multipoles to radiative and non-radiative decay of a single dipole emitter close to a spherical metallic nanoparticle is re-examined. Taking a Ag spherical nanoparticle (AgNP) with the radius of 5 nm as an example, a significant contribution (between 50% and 101% of the total value) of higher-order multipoles to non-radiative rates is found even at the emitter distance of 5 nm from the AgNP surface. On the other hand, the higher-order multipole contribution to radiative rates is negligible. Consequently, a dipole-dipole approximation can yield only an upper bound on the apparent quantum yield. In contrast, the non-radiative rates calculated with the quasistatic Gersten and Nitzan method are found to be in much better agreement with exact electrodynamic results. Finally, the size corrected metal dielectric function is shown to decrease the non-radiative rates near the dipolar surface plasmon resonance.     

近似声斗篷的多层介质覆盖水中弹性球壳的声散射

对水中弹性球壳的低频覆盖层消声效果和消声机理进行研究。声斗篷(Acoustic cloak)是各向异性的超常材料,根据有效介质近似理论(Effective MediumApproximationTheory),采用各向同性多层介质近似各向异性材料的声斗篷,推导出覆盖多层介质水中弹性球壳散射声场的解析表达式,计算了弹性球壳覆盖多层介质前后的散射形态函数、谐振模态以及声场分布,分析了覆盖前后球壳的声散射特性和声传播机理。研究表明,覆盖层内的声波在多层介质之间的声传播方向发生改变,声场形成弯曲变形,声能流绕过目标,这不仅极大的降低了低频散射强度,而且使到达弹性体表面的声场强度非常小,散射频响中除了0阶子波产生的第一个谐振峰外,无法激发弹性球壳的其它谐振模态,有效的抑制弹性球壳的谐振散射。      

Relativistic radiative transition rates and energies for the Li-like isoelectronic sequence: Electric and magnetic dipole and quadropole radiation

For Li-like ions in the isoelectronic sequence between the nuclear charges Z = 26 and 94, energies, oscillator strengths and probabilities of electric and magnetic dipole and quadropole transitions between the first 22 atomic levels were calculated by means of the multiconfigurational Dirac-Fock model. The effects of nonlocal Breit interaction, electron self-energy and vacuum polarization were included in calculating energy levels and radiative rates. The trends of transition energies and rates along the isoelectronic sequence, in particular, the enhancement of the forbidden transitions with increasing atomic number Z, are discussed.     

The Λ particle as a probe of deeply bound single particle states in heavy nuclei

Decay rates of excited states in heavy hypernuclei have been calculated using shell model wave functions. The nuclear Auger effect determines the widths of the states in most cases. The exception is the radiative decay for theΛ particle in the 1p and in exceptional cases also 1d shell. In general, the natural widths of the highly excited states below the threshold for theΛ emission are smaller than the spacing between theΛ shells. Spectroscopy ofΛ bound states in heavy hypernuclei thus seems to be feasible.