Magnetic Dipole Emission Research Articles

The temperature dependence studies of rare-earth (Dy3+, Sm3+, Eu3+ and Tb3+) activated Gd3Ga3Al2O12 garnet single crystals

The luminescence properties of the Dy3+, Sm3+, Eu3+ and Tb3+ activated Gd3Ga3Al2O12 (GGAG) single crystals were investigated as a function of temperature. The photoluminescence excitation, emission and decay kinetic analysis revealed an efficient energy transfer from Gd3+ ions towards all the Dy3+, Sm3+, Eu3+ and Tb3+ activators. The intensity ratio between electric dipole and magnetic dipole emission transitions in activator׳s ions suggested a high homogeneity of the host lattice grown by Czochralski technique. Only the Gd3Ga3Al2O12 single crystal activated with Dy3+ ions exhibited a stable luminescence up to 800K. The Sm3+, Eu3+ and Tb3+ doped Gd3Ga3Al2O12 single crystals showed the onset of the thermal quenching of luminescence at lower temperatures. We proposed three different models, very well-known from the literature, to explain the mechanisms responsible for thermal quenching of activator׳s luminescence in Gd3Ga3Al2O12 single crystal.

High braking index pulsar PSR J1640-4631: low-mass neutron star with a large inclination angle?

Recent timing observation constrained the braking index of the X-ray pulsar PSR J1640-4631 to be $n=3.15\pm0.03$, which is the highest value of all pulsars with measured braking indices so far. In this Letter, we investigate whether pulsar braking by combined between the magnetic dipole emission and the gravitational radiation might have a braking index greater than three. For conventional neutron star and low mass quark star candidates, the inferred ellipticities derived by the observed braking index are obviously much larger than the theoretical estimated maximum value. If PSR J1640-4631 is a low-mass neutron star with a mass of $0.1~ \rm M_{\odot}$, the inferred ellipticity can be approximately equal to the theoretical estimated maximum value. Because of the radio-quiet nature of this source, we employ the vacuum gap model developed by Ruderman and Sutherland to constrain the inclination angle to be $87.2-90^{\circ}$. Based on this, we propose that a low-mass neutron star with a large inclination angle can interpret the high braking index and the radio-quiet nature of this source. Future observations such as gravitational wave detection and long-term timing for this source are required to confirm or confute our scenario.

Eu3+-Doped Wide Band Gap Zn2SnO4 Semiconductor Nanoparticles: Structure and Luminescence

Nanocrystalline Zn2SnO4 powders doped with Eu3+ ions were synthesized via a mechanochemical solid-state reaction method followed by postannealing in air at 1200 °C. X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and Raman and photoluminescence (PL) spectroscopies provide convincing evidence for the incorporation of Eu3+ ions into the host matrix on noncentrosymmetric sites of the cubic inverse spinel lattice. Microstructural analysis shows that the crystalline grain size decreases with the addition of Eu3+. Formation of a nanocrystalline Eu2Sn2O7 secondary phase is also observed. Luminescence spectra of Eu3+-doped samples show several emissions, including narrow-band magnetic dipole emission at 595 nm and electric dipole emission at 615 nm of the Eu3+ ions. Excitation spectra and lifetime measurements suggest that Eu3+ ions are incorporated at only one symmetry site. According to the crystal field theory, it is assumed that Eu3+ ions participate at octahedral sites of Zn2+ or Sn4+ under a weak cr...

A CASE AGAINST SPINNING PAHS AS THE SOURCE OF THE ANOMALOUS MICROWAVE EMISSION

ABSTRACT We employ an all-sky map of the anomalous microwave emission (AME) produced by component separation of the microwave sky to study correlations between the AME and Galactic dust properties. We find that while the AME is highly correlated with all tracers of dust emission, the best predictor of the AME strength is the dust radiance. Fluctuations in the AME intensity per dust radiance are uncorrelated with fluctuations in the emission from polycyclic aromatic hydrocarbons (PAHs), casting doubt on the association between AME and PAHs. The PAH abundance is strongly correlated with the dust optical depth and dust radiance, consistent with PAH destruction in low density regions. We find that the AME intensity increases with increasing radiation field strength, at variance with predictions from the spinning dust hypothesis. Finally, the temperature dependence of the AME per dust radiance disfavors the interpretation of the AME as thermal emission. A reconsideration of other AME carriers, such as ultrasmall silicates, and other emission mechanisms, such as magnetic dipole emission, is warranted.

Strongly Enhanced Raman Optical Activity in Molecules by Magnetic Response of Nanoparticles

An analytical theory for the surface-enhanced Raman optical activity (SEROA) with the magnetic response of the substrate particle has been presented. We have demonstrated that the SEROA signal is proportional to the magnetic polarizability of the substrate particle, which can be significantly enhanced due to the existence of the magnetic response. At the same time, a large circular intensity difference (CID) for the SEROA can also be achieved in the presence of the magnetic response. Taking Si nanoparticles as examples, we have found that the CID enhanced by a Si nanoparticle is 10 times larger than that of Au. Furthermore, when the molecule is located in the hotspot of a Si dimer, CID can be 60 times larger. The phenomena originate from large magnetic fields concentrated near the nanoparticle and boosted magnetic dipole emission of the molecule. The symmetric breaking of the electric fields caused by the magnetic dipole response of the nanoparticle also plays an important role. Our findings provide a new way to tailor theRaman optical activity by designing metamaterials with the strong magnetic response.

Enhancement of magnetic dipole emission at yellow light with polarization-independent hexagonally arrayed nanorods optical metamaterials

Here we demonstrate the control of magnetic dipole spontaneous emission at yellow light by polarization-independent hexagonally arrayed nanorods magnetic metamaterials. By embedding a magnetic dipole into a polarization-independent magnetic metamaterial consisting of hexagonal arrays of paired silver nanorods, the radiative emission enhancement and the Purcell factor around 590 nm have been dramatically increased 44 times for a significant general far-field emission enhancement and 57 times for a maximum general magnetic dipole near-field emission enhancement, respectively. Moreover, the polarization-independent enhancements are found to be a robust variation of the dipole’s positions and structure geometries, showing nice fabrication tolerance for practical applications.

Strong Modification of Magnetic Dipole Emission through Diabolo Nanoantennas

Magnetic dipole transitions in matter are known to be orders of magnitude weaker than their electric dipole counterparts. Nanophotonic and plasmonic structures have the potential of strongly enhancing the optical magnetic fields in the near field, making these nanostructures ideal candidates to control and enhance the emission of magnetic dipole transitions. Here we theoretically investigate the potential of resonant optical nanoantennas based on diabolo and on metal–insulator–metal diabolo configurations to strongly modify the magnetic dipole of emitters. We find that both configurations provide unprecedented 102- to 103-fold enhancement of the total and the radiative decay rates of a magnetic dipole moment. We show that these two nanoantennas have opposed effects on the quantum yield of the magnetic dipole, translating into different antenna efficiencies. Furthermore, by using a magnetic dipole moment as a theoretical optical nanosensor, we numerically mapped the behavior of the magnetic local density o...

Antiquenching effect of modifying cations on samarium clustering: Physical, structural and luminescent behavior of heavy metal borate glass systems

In this paper an attempt has been made to correlate the structural modifications and luminescence efficiencies by changing the environment of the glass network by modifying oxides. Sm3+ doped lead borate (SPB) and lead cadmium alumino borate (SCPB) glasses have been fabricated by melt quench technique at high temperature. The glass samples are characterized by XRD, FTIR, optical absorptions, fluorescence and density measurements. The effect of Sm3+ ion and glass host interaction on the emission spectra has been discussed in the view of the ionicity and covalency of hosts. The ratio of the intensities of electric to magnetic dipole emissions are calculated by varying both the concentration of the Sm3+ ion and the composition of the glass matrix. The XRD profile of all the glasses confirms their amorphous nature and FTIR spectrum shows the presence of BO3 and BO4 groups. These glasses have shown strong absorption bands in the visible (VIS and NIR) region and emit strong orange red wavelengths when excited by ultraviolet light. The concentration quenching has been noticed and ascribed to energy transfer through cross-relaxation between Sm3+ ions. Shifting of UV absorption edge towards longer wavelength with addition of Sm2O3 concentration has been observed. Incorporation of Al2O3 and CdO in 2nd glass system is responsible for strong effect on luminescence of the present glass system. Based on these results, an attempt has been made to throw some light on the relationship between the structural modifications and luminescence efficiencies in two different glass hosts as a laser active medium in the visible region. Moreover the optical basicity values were theoretically determined along with covalent behavior of two glass systems.

Some comments on the electrodynamics of binary pulsars

We consider the electrodynamics of in-spiraling binary pulsars, showing that there are two distinct ways in which they may emit radiation. On the one hand, even if the pulsars do not rotate, we show that in vacuo orbital rotation generates magnetic quadrupole emission, which, in the late stages of the binary evolution becomes nearly as effective as magnetic dipole emission by a millisecond pulsar. On the other hand, we show that interactions of the two magnetic fields generate powerful induction electric fields, which cannot be screened by a suitable distribution of charges and currents like they are in isolated pulsars. We compute approximate electromotive forces for this case.

Sensitization of Rare Earth Ions with Carbon Nanotube Plasmonic Antennas

Complexes containing rare earth ions (REI) and single-walled carbon nanotubes (SWNT) functionalized with single stranded DNA show promise to be utilized for the optical sensing of bio-molecules [1]. However, the electromagnetic interactions between the SWNT and the REI have not been sufficiently studied. In this work, we focus on the plasmonic interaction between the SWNT and a REI such as Terbium or Europium for their use as a biosensing complex. The SWNT may act as a plasmonic antenna and generate a local field in the vicinity of the REI. We use the transmission line model [2] to model the plasmonic properties of the SWNT antenna. The incoming light induces a surface current distribution: I(z)=(V0/Zc)sinh[γp(l/2-|z|)] where V0 is the input voltage into the transmission line model determined by the applied electric field, Zc is the characteristic impedance of the SWNT which is approximately 12 kΩ, γp is the plasmon propogation constant, and l is the length of the tube which we take to be 1 μm. We estimate a field enhancement factor of approximately 106in the near field given by: F=ωl(LC/2)1/2/(k2r2) where L is the kinetic inductance of the SWNT, C is the total capacitance including both electrostatic and quantum capacitances, r is the radial distance between the SWNT axis and the REI, and k and ω are the wavevector and frequency of the incoming light, respectively. The electromagnetic fields will be calculated using the electric Hertz potential satisfying the Helmholtz equation with proper boundary conditions. The conductivity of the SWNT antenna in the transmission line model is given by: σ=iωL-1/(ω2+iωL-1R-C-1L-1 γp 2) where R is the resistance of the SWNT. The interaction of these calculated plasmonic fields with the REI will modulate the lifetimes of the REI. The modulated lifetimes of an electric dipole emitter will be calculated to model the allowed optical transitions of the particular REI. To include the modulations of the optically dark REI transitions, a magnetic dipole emitter will be used. To conclude, these results will give a better understanding of the near field electromagnetic interactions that take place in complexes containing SWNTs and REIs and allow for more efficient sensors. Acknowledgement: This work was supported by: NSF ECCS-1202398

Enhancing Eu(3+) magnetic dipole emission by resonant plasmonic nanostructures.

We demonstrate the enhancement of magnetic dipole spontaneous emission from Eu3+ ions by an engineered plasmonic nanostructure that controls the electromagnetic environment of the emitter. Using an optical microscope setup, an enhancement in the intensity of the Eu3+ magnetic dipole emission was observed for emitters located in close vicinity to a gold nanohole array designed to support plasmonic resonances overlapping with the emission spectrum of the ions.

Enhancement of magnetic dipole emission at yellow light in optical metamaterials

Here we demonstrate the control of magnetic dipole spontaneous emission at yellow light by magnetic metamaterials. By embedding magnetic dipole into a magnetic metamaterial consisting of arrays of paired silver strips, the radiative emission enhancement and the Purcell factor around 590nm has been dramatically increased to 110 and 180 respectively. Moreover, the enhancements are found to be robust to variation of dipole's positions and structure geometries, showing nice fabrication tolerance for practical applications.

Magnetic dipole emission of Dy^3+:Y_2O_3 and Tm^3+:Y_2O_3 at near-infrared wavelengths

Naturally occurring magnetic dipole resonances can be used as optical sources in metamaterials and optical nanostructures to engineer light emission with applications in energy harvesting, biological imaging, and other photonic devices. Here, we use energy-momentum spectroscopy to quantify the electric and magnetic dipole emission rates of near-infrared transitions in Dy3+ and Tm3+ doped Y2O3. Of these emission lines, we find that the overlapping 4F9/2 → 6F11/2 and 4F9/2 → 6H9/2 transitions in Dy3+ and the overlapping 1G4 → 3H5 and 3H4 → 3H6 transitions in Tm3+ exhibit the greatest MD emission and thus offer the most direct pathway for integration with magnetic modes in resonant nanostructures.

Terahertz spectroscopic observation of spin reorientation induced antiferromagnetic mode softening in DyFeO3 ceramics

Dysprosium orthoferrite has been found to undergo the Γ4(Gx,Fz)→Γ1(Gy) spin reorientation transition (Morin transition) at about 37K. In this study, the Morin transition in DyFeO3 ceramic is investigated using a temperature-tunable terahertz spectroscopy system. It is experimentally demonstrated that the DyFeO3 ceramics exhibit obvious terahertz absorption and emission at the antiferromagnetic resonant frequency. It is also shown that the lifetime of magnetic dipole emission remarkably shortens and the quasi-antiferromagnetic mode softens below 198K, which can be ascribed to the decreased terahertz absorption and reduced internal magnetic field induced by the spin reorientation, respectively. This contributes to the research of rare earth orthoferrites׳ terahertz electromagnetic properties.

Planck intermediate results

The dust-HI correlation is used to characterize the emission properties of dust in the diffuse interstellar medium. We cross-correlate sky maps from Planck, WMAP, and DIRBE, at 17 frequencies from 23 to 3000 GHz, with the Parkes survey of the 21-cm line emission of neutral atomic hydrogen, over a contiguous area of 7500 deg$^2$ centred on the southern Galactic pole. Our analysis yields four specific results. (1) The dust temperature is observed to be anti-correlated with the dust emissivity and opacity. We interpret this result as evidence for dust evolution within the diffuse ISM. The mean dust opacity is measured to be $(7.1 \pm 0.6) 10^{-27} cm^2/H \times (\nu/353\, GHz)^{1.53\pm0.03}$ for $100 < \nu <353$GHz. (2) We map the spectral index of dust emission at millimetre wavelengths, which is remarkably constant at $\beta_{mm} = 1.51\pm 0.13$. We compare it with the far infrared spectral index beta_FIR derived from greybody fits at higher frequencies, and find a systematic difference, $\beta_{mm}-\beta_{FIR} = -0.15$, which suggests that the dust SED flattens at $\nu < 353\,$GHz. (3) We present spectral fits of the microwave emission correlated with HI from 23 to 353 GHz, which separate dust and anomalous microwave emission. The flattening of the dust SED can be accounted for with an additional component with a blackbody spectrum, which accounts for $(26 \pm 6)$% of the dust emission at 100 GHz and could represent magnetic dipole emission. Alternatively, it could account for an increasing contribution of carbon dust, or a flattening of the emissivity of amorphous silicates, at millimetre wavelengths. These interpretations make different predictions for the dust polarization SED. (4) We identify a Galactic contribution to the residuals of the dust-HI correlation, which we model with variations of the dust emissivity on angular scales smaller than that of our correlation analysis.

Spontaneous emission of electric and magnetic dipoles in the vicinity of thin and thick metal

Strong modification of spontaneous emission of Eu(3+) ions placed in close vicinity to thin and thick gold and silver films was clearly demonstrated in a microscope setup separately for electric and magnetic dipole transitions. We have shown that the magnetic transition was very sensitive to the thickness of the gold substrate and behaved distinctly different from the electric transition. The observations were described theoretically based on the dyadic Green's function approach for layered media and explained through modified image models for the near and far-field emissions. We established that there exists a "near-field event horizon", which demarcates the distance from the metal at which the dipole emission is taken up exclusively in the near field.

Numerical investigation of coupling efficiency between a magnetic line dipole emitter and surface plasmon polariton modes of a nanometer thin metallic film

In this paper we considered a line magnetic dipole emitter near a 25nm thick silver film embedded in a homogeneous dielectric environment. By using a two dimensional magnetic Green's function, the Purcell factor and coupling efficiency factor (β factor) for symmetric and antisymmetric surface plasmon polaritons (SPP) and out of plane (OUP) propagating decay channels were calculated. For a fixed wavelength emission, the effects of source position and refractive index of the dielectric medium on the Purcell factor and β factors are investigated.The numerical results show that, where the Purcell factor is maximum (minimum) the antisymmetric (symmetric) SPP is dominant decay channel and the selective excitation of symmetric SPP is better achievable in the case in which the dielectric medium has the higher refractive index. The wavelength dependency of β factors is also investigated for different source locations. This investigation shows that how the wavelength position for the peak of β factors depends on source location. The results of this paper could have implications for metamaterials research and many lanthanides based photonic devices.

Modification of electric and magnetic dipole emission in anisotropic plasmonic systems

In order to investigate the effects of plasmonic environments on spontaneous emission of magnetic and electric dipoles, we have studied luminescence of Eu³⁺ ions in close vicinity to gold nanostrip arrays. Significant changes in the emission kinetics, emission polarization, and radiation patterns have been observed in the wavelength range corresponding to the plasmonic resonance. The effect of the plasmonic resonance on the magnetic dipole transition ⁵D₀-->⁷F₁ is found to be very different from its effect on the electric dipole transitions. This makes Eu³⁺₋ containing complexes promising for mapping local distributions of magnetic and electric fields in metamaterials and plasmonic systems.

Tailoring Magnetic Dipole Emission with Plasmonic Split-Ring Resonators

We numerically explore the emission behavior of magnetic dipole emitters located next to resonant plasmonic split-ring resonators (SRRs), which are well known for their large magnetic moment at their fundamental resonance in the near infrared. Our results are compared to the situation for electric dipole emitters, where the SRR can be described by solely its electric dipole moment. We show that a similar approach in the case of magnetic dipole emitters is not sufficient, as the symmetry breaking due to the gap has to be taken into account. We demonstrate how retardation between the emitter and the SRR can be used as an additional degree of freedom to manipulate the emission spectrum. Our concept will pave the road towards efficient plasmonic antennas for magnetic dipole emitters.

MAGNETIC NANOPARTICLES IN THE INTERSTELLAR MEDIUM: EMISSION SPECTRUM AND POLARIZATION

The presence of ferromagnetic or ferrimagnetic nanoparticles in the interstellar medium would give rise to magnetic dipole radiation at microwave and submm frequencies. Such grains may account for the strong mm-wavelength emission observed from a number of low-metallicity galaxies, including the Small Magellanic Cloud. We show how to calculate the absorption and scattering cross sections for such grains, with particular attention to metallic Fe, magnetite Fe3O4, and maghemite gamma-Fe2O3, all potentially present in the interstellar medium. The rate of Davis-Greenstein alignment by magnetic dissipation is also estimated. We determine the temperature of free-flying magnetic grains heated by starlight and we calculate the polarization of the magnetic dipole emission from both free-fliers and inclusions. For inclusions, the magnetic dipole emission is expected to be polarized orthogonally relative to the normal electric dipole radiation. Finally, we present self-consistent dielectric functions for metallic Fe, magnetite Fe3O4, and maghemite gamma-Fe2O3, enabling calculation of absorption and scattering cross sections from microwave to X-ray wavelengths.