Radiative Emission Rate Research Articles

Fermion analysis of IR modified Hořava–Lifshitz gravity: tunneling and perturbation perspectives

In this paper, we investigate the fermion Hawking radiation and quasinormal (QN) modes in infrared (IR) modified Hořava–Lifshitz (HL) gravity under tunneling and perturbation perspectives. Firstly, through the fermion tunneling in IR modified HL gravity, we obtain the Hawking radiation emission rate, tunneling temperature and entropy for the Kehagias–Sfetsos black hole. It is found that the results of fermion tunneling are consistent with the thermodynamics results obtained by calculating surface gravity. Secondly, we numerically calculate the low-lying QN mode frequencies of fermion perturbations by using WKB formulas including the third-order and sixth-order approximations simultaneously. It turns out that the actual frequency of fermion perturbation is larger than that in the Schwarzschild case, and the damping rate is smaller than that for the pure Schwarzschild. The results of fermion perturbation suggest the QN modes could live longer in HL gravity.

Lα,Lβ, andLγx-ray production cross sections of Hf, Ta, W, Re, Os, Au, Pb, and Bi by electron impact: Comparison of distorted-wave calculations with experiment

We study the emission of $L\ensuremath{\alpha}$, $L\ensuremath{\beta}$, and $L\ensuremath{\gamma}$ characteristic x rays by the impact of electrons on Hf, Ta, W, Re, Os, Au, Pb, and Bi atoms. To this end, ionization cross sections of the ${L}_{1}$, ${L}_{2}$, and ${L}_{3}$ subshells of these atoms are calculated within the distorted-wave Born approximation. The considered energy interval spans from the ionization threshold up to 50 keV. Atomic relaxation parameters (i.e., Coster-Kronig and radiative transition probabilities, fluorescence yields, and emission rates) taken from the literature are then used to evaluate x-ray production cross sections. The theoretical predictions are compared with published experimental information. Good agreement is found for Ta, W, Os, Au, Pb, and Bi. In the case of Hf and Re, the measured cross sections are lower than the theoretical estimates by around 30%. The observed discrepancies might be attributed to the methods employed to correct the raw experimental data for the excess of detected characteristic x rays caused by the finite thickness of the sample's active layer and the presence of the thick substrate.

Infrared luminescence of Tm3+/Yb3+ codoped lanthanum aluminum germanate glasses

Tm 3 + doped and Tm3+/Yb3+ codoped lanthanum aluminum germanate (LAG) glasses are prepared by melt-quenching method and characterized optically. Based on the measurement of absorption spectrum, Judd–Ofelt intensity parameters (Ω2,Ω4,Ω6) are calculated. The radiation emission rates, branching ratios, and lifetimes of Tm3+ are calculated to evaluate the spectroscopic properties of Tm3+ in LAG glass. The infrared emission properties of the samples are investigated and the results show that the 1.8 μm emission can be greatly enhanced by adding proper amount of Yb3+ under the excitation of 980 nm. The energy transfer processes of Yb3+–Yb3+ and Yb3+–Tm3+ are analyzed, and the results show that Yb3+ ions can transfer their energy to Tm3+ ions with high efficiency and large energy transfer coefficient.

Boron spectral line ratios helpful to characterize wall conditioned tokamak plasmas

The intensity ratios of spectral lines of a single species are often used as diagnostics for inferring the electron temperature or density in plasmas. Helium is a well-known example. In this paper, the atomic data and analysis structure (ADAS) database has been used to identify line ratios in boron that might prove useful for plasmas created in tokamaks for the wall conditioning of plasma-facing-surfaces. Using the collisional radiative (CR) model-based photon emission rate coefficients, a few line intensity ratios selectively sensitive only to temperature and those that are sensitive to density are presented.

Large single-molecule fluorescence enhancements produced by a bowtie nanoantenna

A 1,340-fold increase in single-molecule fluorescence has been observed from a lithographically fabricated gold bowtie nanoantenna — approximately an order of magnitude greater than that achieved in previous reports on such structures. The improvement results from an estimated ninefold increase in quantum efficiency, caused by enhanced absorption and an increased radiative emission rate.

Enhancement of Excimer Fluorescence from Thin Dye Film by Single Gold Nanoparticles

Abstract We studied the enhancement of excimer emission from a thin perylene dye film (10-nm thickness) by localized surface plasmon resonance (LSPR) of single gold nanoparticles (GNPs), and observed a large fluorescence enhancement factor of about 25. The absence of excitation wavelength dependence of the enhancement factor indicates that the fluorescence intensity enhancement is mainly due to an increase of the radiative emission rate by LSPR.

Laboratory modeling of supersonic radiative jets propagation in plasmas and their scaling to astrophysical conditions

Supersonic jets propagation over considerable distances and their interactions with surrounding media is one of the important subjects in astrophysics. Laboratory-created jets have completely different scales, however, typical velocities are the same, and the similarity criteria can be applied to scale them to astrophysical conditions. Moreover, by choosing appropriate pairs of colliding plasmas, one can fulfil the scaling conditions for the radiation emission rates. In this paper we present the results of studies of interaction of laser-created jets with gas-puff plasmas at the PALS laser facility. By varying the gas pressure and composition, the nature of the interaction zone changes from a quasi-adiabatic outflow to a strongly radiation cooling jet. The fine scale structures of the interaction zone are studied by means of optical and x-ray diagnostics, and they are interpreted with a semi-analytical model and 2D radiation hydrodynamic simulations. The conclusions from the laboratory experiment are scaled to the astrophysical conditions.

A method to assess modifications of fluorophore radiative rate by plasmonic structures

We present a method for assessing radiative emission rates of the fluorophores by plasmonic metal structures by using fluorescence lifetime and cathodoluminescence measurements. By using this approach we identified and quantified the increased radiative rate of a Deep Purple fluorophore in inverted pyramidal pits of gold nanostructured arrays (Klarite) compared with the radiative rate of the same fluorophore on planar gold. This increased rate is attributed to the effect of localized surface plasmons preferentially concentrated in the pits of these arrays.

Tunable surface plasmons for emission enhancement of silicon nanocrystals using Ag-poor cermet layer

To improve the quantum efficiency from silicon nanocrystals, a structure with Ag∕Ag-poor cermet layers is proposed. Due to large permittivity of Ag-poor cermet and its dispersion characteristic, density of states can be enhanced at the energy much lower than the plasmon energy of Ag. By properly choosing the component of the Ag-poor cermet, the dispersion of surface plasmons can be engineered to increase radiative emission rate significantly at the emission energy of silicon nanocrystals. Effective enhancement is theoretically demonstrated using Ag, which was generally recognized as nonideal material for emission enhancement in silicon nanocrystals due to its high plasmon energy.

Cavity-enhanced radiative emission rate in a single-photon-emitting diode operating at 0.5 GHz

We report the observation of a Purcell enhancement in the radiative decay rate of a single quantum dot, embedded in a microcavity light-emitting-diode structure. Lateral confinement of the optical mode was achieved using an annulus of low-refractive-index aluminium oxide, formed by wet oxidation. The same layer acts as a current aperture, reducing the active area of the device without impeding the electrical properties of the p-i-n diode. This allowed single photon electroluminescence to be demonstrated at repetition rates up to 0.5 GHz.

Enhanced radiative emission rate of CdSe/ZnS quantum dots on semi-continuous gold films

We have studied the enhancement of radiative emission rate of CdSe/ZnS core-shell quantum dots on semi-continuous gold films which have been prepared by using sputtering technique. The photoluminescence intensity and the decay rate of CdSe/ZnS quantum dots are affected by the semi-continuous gold films. Both the photoluminescence intensity and the decay rate of the quantum dots are greatly enhanced by the semi-continuous gold films near the conductive percolation threshold and that are caused by the enhanced local electric field due to the surface plasmon resonance on the semi-continuous gold films.

Study on a set of bis-cyclometalated Ir(iii) complexes with a common ancillary ligand

Bis-cyclometalated iridium(III) complexes [Ir(F2ppy)2ZN] (FZN), [Ir(F2CNppy)2ZN] (FCZN), [Ir(DMAF2ppy)2ZN] (FDZN) and [Ir(MeOF2ppy)2ZN] (MeOFZN) (F2ppy = 4',6'-difluoro-2-phenylpyridinate, F2CNppy = 5-cyano-4',6'-difluoro-2-phenylpyridinate, DMAF2ppy = 4',6'-difluoro-4-dimethylamino-2-phenylpyridinate, MeOF2ppy = 4',6'-difluoro-4-methyl-2-phenylpyridinate and ZN = 3,5-dimethylpyrazole-N-carboxamide) emitting in the sky blue region were synthesized. We studied the effect of the ancillary ligand ZN and the substituents on the cyclometalating ligands on the crystal structures, photophysical and electrochemical properties and the frontier orbitals. Density functional theory (DFT) calculation results indicate that in FCZN and FDZN the cyclometalating ligands show negligible participation in the HOMO, the ancillary ligand ZN being the main participant along with the Ir(III) d-orbitals. MeOFZN exhibits the maximum photoluminescence quantum efficiency and radiative emission rates along with the dominant low frequency metal-ligand vibrations and maximum reorganization energy in the excited state. All the substituted complexes show more polar characteristics than FZN, FCZN possessing the highest dipole moment among the complexes. The performances of the solution-synthesised organic light emitting devices (OLEDs) of FZN, FCZN and FDZN doped in a blend of mCP (m-bis(N-carbazolylbenzene)) and polystyrene are studied.

Greybody factors in a rotating black-hole background: Fermions and gauge bosons

We study the emission of fermion and gauge boson degrees of freedom on the brane by a rotating higher-dimensional black hole. Using matching techniques, for the near-horizon and far-field regime solutions, we solve analytically the corresponding field equations of motion. From this, we derive analytical results for the absorption probabilities and Hawking radiation emission rates, in the low-energy and low-rotation case, for both species of fields. We produce plots of these, comparing them to existing exact numerical results with very good agreement. We also study the total absorption cross-section and demonstrate that, as in the non-rotating case, it has a different behaviour for fermions and gauge bosons in the low-energy limit, while it follows a universal behaviour – reaching a constant, spin-independent, asymptotic value – in the high-energy regime.

Measurements of L X-ray production cross sections, L subshell fluorescence yields and K to L shell vacancy transfer probabilities

L i X-ray production cross sections have been measured for Sm, Eu, Gd, Dy, Ho, Er, Pt, Au, Tl, Pb and Bi at 59.54 keV incident photon energy. The values of L i subshell fluorescence yields ( ω 1, ω 2 and ω 3) have been determined using the presently measured X-ray production cross sections and the theoretical L i subshell photoionization cross sections values, Coster–Kronig transition probabilities and radiative emission rates. Furthermore, K to L shell vacancy transfer probabilities η KL i ( i=1, 2, 3) for Sm, Eu, Gd, Dy, Ho, Er were determined by measuring the L X-ray production cross section and L subshell fluorescence yields. The measurements were performed using an Am-241 radioisotope as the photon source and a Si(Li) detector. The measured X-ray production cross sections, fluorescence yields and vacancy transfer probabilities were compared with the theoretical values. The results in the present paper are found to be in good agreement with the calculated values.

Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals

We observe experimentally that ensembles of quantum dots in three-dimensional (3D) photonic crystals reveal strongly nonexponential time-resolved emission. These complex emission decay curves are analyzed with a continuous distribution of decay rates. The log-normal distribution describes the decays well for all studied lattice parameters. The distribution width is identified with variations of the radiative emission rates of quantum dots with various positions and dipole orientations in the unit cell. We find a striking sixfold change of the width of the distribution by varying the lattice parameter. This interpretation qualitatively agrees with the calculations of the 3D projected local density of states. We therefore conclude that fluorescence decay of ensembles of quantum dots is highly nonexponential to an extent that is controlled by photonic crystals.

Photoluminescent behavior of SrB 4O 7: RE2+ ( RE=Sm and Eu) prepared by Pechini, combustion and ceramic methods

This work reports the preparation of system containing RE 2+ ions ( RE=Sm and Eu)-doped in SrB 4O 7 matrix by ceramic, Pechini and combustion methods. These compounds were prepared by reduction of RE 3+ to RE 2+ in air, which exhibit some different features according to the preparation method. Photoluminescent properties of these systems were investigated based on the emission and excitation spectral data. The emission spectra of SrB 4O 7:Eu 2+ system prepared by combustion and Pechini methods are characterized by a broad band assigned to interconfigurational 4 f 65 d→4 f 7 transition, while SrB 4O 7:Sm 2+ compound exhibit narrow emission bands arising from intraconfigurational-4 f 6 also shows 4 G 5/2→ 6 H J′ transitions ( J ′ = 5 2 , 7 2 , 9 2 and 11 2 ) arising from Sm 3+ ion, transitions. SrB 4O 7: RE system prepared by combustion method presents emission bands from RE 3+ ions as intense as that arising from RE 2+, suggesting that the preparation route is not efficient for the reduction RE 3+→ RE 2+ process. Emission quantum efficiency and radiative emission rates of Sm 2+ ion are determined and discussed.

Measurement of the radiative vacancy transfer probabilities from the L 3 to M and to N shells for W, Re and Pb using synchrotron radiation

The radiative vacancy transfer probabilities from L 3 to M shell, η L 3 M ( R ) and L 3 to N shell, η L 3 N ( R ) , have been determined for W, Re and Pb. The pure elements samples were excited by monochromatic synchrotron radiation. The X-rays were generated by excitation of L 3 edge and measured using a high resolution Si(Li) detector. The experimentally determined radiative vacancy transfer probabilities were compared with the theoretical values deduced using radiative X-ray emission rates based on the relativistic Dirac–Hartree–Slater (RDHS) model. In the case of Pb, the experimental data were compared as well with experimental values of Simsek. In both cases, a good agreement was found between the datasets.

Silicon Nanocrystal Field-Effect Light-Emitting Devices

We describe the operation of a light-emitting device in which silicon nanocrystals are electrically pumped via the field-effect electroluminescence (EL) mechanism. In contrast to the simultaneous bipolar carrier injection used in conventional p-n junction light-emitting diodes, this device employs sequential unipolar programming of both electrons and holes across a tunneling barrier from the same semiconductor channel. Light emission is strongly correlated with the injection of second carriers into nanocrystals that have been previously programmed with charges of the opposite sign. The properties of this device are well described by the model of a charge injection through Coulomb field modified tunneling processes. We additionally consider limiting performance bounds for potential future devices fabricated from nanocrystals with different radiative emission rates

Hawking radiation from a [formula omitted]-dimensional rotating black hole on the brane

We study the emission of Hawking radiation in the form of scalar fields from a (4+n)-dimensional, rotating black hole on the brane. We perform a numerical analysis to solve both the radial and angular parts of the scalar field equation, and derive exact results for the Hawking radiation energy emission rate. We find that, in 5 dimensions, as the angular momentum increases, the emission rate is suppressed in the low-energy regime but significantly enhanced in the intermediate and high-energy regimes. For higher values of n, the Hawking radiation emission rate on the brane is significantly enhanced, with the angular momentum, over the whole energy regime. We also investigate the energy amplification due to the effect of super-radiance and demonstrate that, in the presence of extra dimensions, this effect is again significantly enhanced.

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters