Highly Efficient and Thermally Stable Eu2+-Doped Ca9Nd(PO4)7 Phosphor for Near-Ultraviolet White-Emission LED Applications

Various Eu2+-based Ca9Nd(PO4)7 (CNP:xEu2+, with different x values) materials are prepared via facile solid-state reaction. Their crystal structures are investigated in detail by means of the Rietveld refinement. The structure of CNP:Eu2+ with a trigonal lattice is analogous to that of β-Ca3(PO4)2. Therefore, Eu2+ ions tend to incorporate calcium sites in the host. All the obtained samples can be excited using near ultraviolet (nUV) light to present blue-green emission. An optimal dopant concentration is verified at x = 0.8 with a large critical interaction radius (11.21 Å). The mechanism of the concentration quenching effect is assigned to the multipole-multipole interaction. CNP:xEu2+ possesses a short decay lifetime of ∼60 μs and can endure severe working conditions thanks to its great thermal stability. The relative photoluminescence (PL) intensity of CNP:0.8Eu2+ can retain 84.75% of the pristine intensity measured at room temperature, and the relative intensity remains as high as 69.97% at 423 K. The CNP:Eu2+ phosphors also show great performance in the WLED demonstration. The correlated color temperature (CCT) of the prototype device is 3404 K, with an extremely high Ra (97.6). Therefore, CNP:xEu2+ could be regarded as a promising alternative to blue green phosphors in nUV chip-based WLED applications.

Preparation and luminescence properties of Tm3+-doped SrBi2Ta2O9 blue-emitting phosphor

Various novel SrBi2Ta2O9:Tm3+ blue-emitting materials were achieved via solid-state synthesis. The structure and phase purity of prepared SrBi2Ta2O9:xTm3+ (x = 0.005-0.30 mol) were examined by X-ray powder diffraction. The surface morphology of SrBi2Ta2O9:0.01Tm3+ were studied by scanning electron microscopy. Photoluminescence properties were systematically explored under the monitoring emission (λem = 468 nm) and excitation (λex = 303 nm) spectra. The optimum mole ratio of as-synthesized phosphors was 0.01 mol. The concentration quenching mechanism in the SrBi2Ta2O9 host was due to electric multipole interaction. Particularly, the chromaticity coordinates (0.1334, 0.0474) of SrBi2Ta2O9:0.01Tm3+ are near to those of the commercial BaMgAl10O17:Eu2+. These results validated the SrBi2Ta2O9:Tm3+ phosphor can be utilized good blue-emitting candidate for W-LEDs.

Synthesis, characterization and photoluminescence properties of Tm3+-doped Ca2YTaO6 blue-emitting phosphors

A series of Ca2YTaO6: Tm3+ blue-emitting phosphors were firstly prepared by the solid-state method. The phase formations and purity of Ca2YTaO6: xTm3+ (x = 0.3%-5% mol) were verified by X-ray powder diffraction. The morphological characteristics of Ca2YTaO6: 0.005Tm3+ were detected by scanning electron microscopy (SEM). Photoluminescence properties were discussed by emission (λem = 460 nm) and excitation (λex = 359 nm) spectra. The critical doping concentration of the products was 0.005 mol. The proposed concentration quenching mechanism in Ca2YTaO6 materials was the electric multipole interaction. Besides, the color coordinates (0.1408, 0.0891) of Ca2YTaO6: 0.005Tm3+ were located in blue region. The results suggested the Ca2YTaO6: Tm3+ phosphors can be promising blue-emitting components for the WLED applications.

New LHCb pentaquarks as hadrocharmonium states

New LHCb Collaboration results on pentaquarks with hidden charm1 are discussed. These results fit nicely in the hadrocharmonium pentaquark scenario.[Formula: see text] In the new data the old LHCb pentaquark [Formula: see text] splits into two states [Formula: see text] and [Formula: see text]. We interpret these two almost degenerated hadrocharmonium states with [Formula: see text] and [Formula: see text], as a result of hyperfine splitting between hadrocharmonium states predicted in Ref. 2. It arises due to QCD multipole interaction between color-singlet hadrocharmonium constituents. We improve the theoretical estimate of hyperfine splitting[Formula: see text] that is compatible with the experimental data. The new [Formula: see text] state finds a natural explanation as a bound state of [Formula: see text] and a nucleon, with [Formula: see text], [Formula: see text] and binding energy 42 MeV. As a bound state of a spin-[Formula: see text] meson and a nucleon, hadrocharmonium pentaquark [Formula: see text] does not experience hyperfine splitting. We find a series of hadrocharmonium states in the vicinity of the wide [Formula: see text] pentaquark that can explain its apparently large decay width. We compare the hadrocharmonium and molecular pentaquark scenarios and discuss their relative advantages and drawbacks.

Interaction and Entanglement of a Pair of Quantum Emitters near a Nanoparticle: Analysis beyond Electric-Dipole Approximation

In this paper, we study the collective effects which appear as a pair of quantum emitters is positioned in close vicinity to a plasmonic nanoparticle. These effects include multipole–multipole interaction and collective decay, the strengths and rates of which are modified by the presence of the nanoparticle. As a result, entanglement is generated between the quantum emitters, which survives in the stationary state. To evaluate these effects, we exploit the Green’s tensor-based quantization scheme in the Markovian limit, taking into account the corrections from light–matter coupling channels higher than the electric dipole. We find these higher-order channels to significantly influence the collective rates and degree of entanglement, and in particular, to qualitatively influence their spatial profiles. Our findings indicate that, apart from quantitatively modifying the results, the higher-order interaction channels may introduce asymmetry into the spatial distribution of the collective response.

Synthesis and photoluminescence properties of Ba2Y3(SiO4)3F:Tm3+ blue-emitting fluorosilicate phosphors

Various novel Ba2Y3(SiO4)3F:Tm3+ blue-emitting fluorosilicate materials were achieved via solid-state synthesis. The structure and phase purity of prepared Ba2Y3(SiO4)3F:xTm3+ (x = 0.001-0.10 mol) were examined by X-ray powder diffraction. The surface morphology of Ba2Y3(SiO4)3F:0.01Tm3+ was studied by scanning electron microscopy. Photoluminescence properties were systematically explored under the monitoring emission (λem = 468 nm) and excitation (λex = 302 nm) spectra. The optimum mole ratio of as-synthesized phosphors was 0.01 mol. The concentration quenching mechanism in the Ba2Y3(SiO4)3F host was due to electric multipole interaction. Particularly, the chromaticity coordinates (0.1334, 0.0474) of Ba2Y3(SiO4)3F:0.01Tm3+ are near to those of the commercial BaMgAl10O17:Eu2+. These results validated the Ba2Y3(SiO4)3F:Tm3+ fluorosilicate phosphor can be used as a good blue-emitting candidate for W-LEDs.

A New Relatively Simple Approach to Multipole Interactions in Either Spherical Harmonics or Cartesians, Suitable for Implementation into Ewald Sums

We present a novel derivation of the multipole interaction (energies, forces and fields) in spherical harmonics, which results in an expression that is able to exactly reproduce the results of earlier Cartesian formulations. Our method follows the derivations of Smith (W. Smith, CCP5 Newsletter 1998, 46, 18.) and Lin (D. Lin, J. Chem. Phys. 2015, 143, 114115), who evaluate the Ewald sum for multipoles in Cartesian form, and then shows how the resulting expressions can be converted into spherical harmonics, where the conversion is performed by establishing a relation between an inner product on the space of symmetric traceless Cartesian tensors, and an inner product on the space of harmonic polynomials on the unit sphere. We also introduce a diagrammatic method for keeping track of the terms in the multipole interaction expression, such that the total electrostatic energy can be viewed as a ‘sum over diagrams’, and where the conversion to spherical harmonics is represented by ‘braiding’ subsets of Cartesian components together. For multipoles of maximum rank n, our algorithm is found to have scaling of n 3.7 vs. n 4.5 for our most optimised Cartesian implementation.

Dual Toroidal Dipole Resonance Metamaterials under a Terahertz Domain

We proposed and fabricated a flexible, planar, U-shape-modified structure metamaterial (MM) that was composed of two metallic pattern layers separated by a polyimide layer, where each metallic pattern layer consists of two U-shaped split ring resonators (USRRs). The coupling effect between the two USRRs in the same metallic layer was vital to the formation of dual toroidal dipole (TD) resonances. The measured and simulated results showed that both low quality factor (Q) (~1.82) and high Q (~10.31) TD resonances were acquired synchronously at two different frequencies in the MMs by adjusting the distance between the two coplanar USRRs. With the interaction of the USRRs, the energy levels of the USRRs were split into inductance-capacitance (LC)-induced TD resonance at low frequency and dipole-induced TD resonance at high frequency. Thus, the electric multipole interaction played an important role in determining the energy level of the TD resonance. The better strength of the high frequency TD resonance can be confined to an electromagnetic field inside a smaller circular region, and thus, a higher Q was obtained. In order to investigate the TD mechanism more in depth, the power of the electric dipole, magnetic dipole, electric circular dipole, and TD were quantitatively calculated. Dual TD MMs on a freestanding substrate will have potential applications in functional terahertz devices for practical applications.