[en] We theoretically investigate the high-order harmonic generation and attosecond pulse generation for a 5 fs, 800 nm left- and right-circularly polarized laser field, which is called polarization gating, combined with a static electric field. We find that quantum trajectory is controlled and the quantum interference is suppressed by the static electric field. For the case of α=0.1, the harmonic spectrum presents a two-plateau structure and the time-frequency analysis shows that only a quantum trajectory is contributed to the second plateau. The single attosecond pulse with a duration of 80 as is obtained by super-posing the super-continuum area of the second plateau 50 eV (160 eV∼210 eV). (authors)

[en] We have developed an analytical dual-frequency model, which results in accurate dual-peaks of the ion energy distributions (IEDs) for the given control parameters. The model can analytically calculate and predict the IEDs dual peaks and energy width with necessary plasma parameters. This model can also predict the IEDs from dual frequencies’ drives at any voltage, the associated results are compared with particle-in-cell (PIC) simulations. The IED at a surface is an important parameter for processing in dual radio frequencies driven capacitive couple discharges. The computing model is developed for the IED in a low pressure discharge based on a linear transfer function that relates the time-varying sheath voltage to the time- varying ion energy response at the surface. This model is in good agreement with PIC simulations over a wide range of dual frequencies driven capacitive couple discharge excitations. (paper)

[en] Graphical abstract: We reported a novel hetero-valence cation exchange route to synthesize Ln: NaGdF4 upconversion nanocrystals for the first time. -- Highlights: • The Ln3+: NaGdF4 nanocrystals were synthesized based on the Ln3+: CaF2 precursors. • The microstructures of nanocrystals were characterized. • The multi-color upconversion emissions were easily realized. -- Abstract: Lanthanide-doped upconversion nanomaterials have attracted great attention recently for their potential applications in the fields of bio-label, three-dimensional display, solar cell and so on. In this article, we report a new strategy to prepare hexagonal Ln³⁺:NaGdF₄ upconversion nanocrystals. Unlike the routine way of synthesizing NaGdF₄ nanocrystals through nucleation and growth, the formation of hexagonal NaGdF₄ nanocrystals herein is realized based on the Ln³⁺-doped cubic CaF₂ precursors, following a hetero-valence cation exchange process between Gd³⁺/Na⁺ and Ca²⁺. Evidently, Ln³⁺ dopants in the CaF₂ precursors are retained in the finally formed hexagonal NaGdF₄ nanocrystals and, subsequently, multi-color upconversion emissions are easily realized by simply adjusting the Ln³⁺ dopant species and contents in the CaF₂ precursors. This novel hetero-valence cation exchange route may open up a new pathway to synthesize nanomaterials that cannot be fabricated directly

[en] The probability of Schwinger pair production is calculated, which is induced by an ultraintense and ultrashort laser pulse propagating in a plasma. The dependence of the probability on the amplitude of the laser pulse and the frequency of plasmas is analyzed. Particularly, the effect of the pulse duration on the probability is discussed, by introducing a pulse-shape function to describe the temporal shape of the laser pulse. The results show that a laser with shorter pulse is more efficient in pair production. The probability of pair production increases when the order of the duration is comparable to the period of a laser. (author)

[en] Electrically conducting polyaniline (PANI)-magnetic oxide (Fe₃ O₄) composites were synthesized by emulsion polymerization in the presence of dodecyl benzene sulfonic acid (DBSA) as the surfactant and dopant and ammonium persulfate (APS) as the oxidant. Transmission electron microscopy (TEM) indicates that the composite has a magnetic core and an electric shell and the modification has prevented the aggregation of Fe₃ O₄ nanoparticles effectively. The electromagnetic parameter measurements (ε-prime, ε', μ-prime and μ') in the range of 2-18 GHz prove that Fe₃ O₄ in the Fe₃ O₄/PANI/DBSA is responsible for the electric and ferromagnetic behavior of the composites. As a result, the electromagnetic parameters can be designed by adjusting the content of the Fe₃ O₄. The microwave absorption of functionally graded material (FGM) was simulated by the computer according to the principle of impedance match and the calculated results agreed quite well with the experimentally measured data (R<-20 dB, Δf>4 GHz)

[en] We investigate the properties of a three-dimensional (3D) dipolar Bose-Einstein condensate (BEC) in a double-well potential (DWP). Symmetry breaking and tunneling dynamics phenomena are demonstrated for ¹⁶⁴Dy atoms in the 3D DWP using an effective two-mode model. The results show that the symmetry properties of the dynamics are affected markedly by the long-range nature and anisotropy of the dipolar interaction and the isotropic contact interaction. (author)

[en] The time-resolved luminescence spectra of the Eu³⁺ doped SiO₂-Al₂O₃-NaF-YF₃-EuF₃ precursor glass reveal that Eu³⁺ ions locate in both the oxygen-coordination environment and the fluorine-coordination one. After crystallization induced by heat treatment, the orthorhombic YF₃ nanocrystals with mean size of 22 nm embedded homogeneously in the glassy matrix. The Stark splitting emission, the low electric dipole ⁵D₀→⁷F₂ transition, the disappearance of the O^2--Eu³⁺ charge transfer band and the reduction in Ω₂ value indicate the partition of Eu³⁺ into the YF₃ lattice. Moreover, the nearly single-exponential luminescence decay curves of the Eu³⁺:⁵D₀ and ⁵D₁ levels for the 0.1%Eu³⁺ doped glass ceramic evidence that Eu³⁺ ions mainly occupy the Y³⁺ sites.

[en] Molecular-like Ag clusters sized at 1–4 nm have been stabilized in Pb/Cd-free oxyfluoride glasses, showing broadband excitation/emission characteristics and unique wavelength-dependent luminescent performance with a maximal quantum yield of 26.9%. It was experimentally demonstrated that an energy transfer route of Ag clusters → Tb³⁺ → Yb³⁺ occurs in Ag⁺/Tb³⁺/Yb³⁺ tri-doped sample, wherein Ag clusters act as sensitizers for near-infrared down-conversion spectral modification. Hopefully, the proposed strategy that noble metal clusters being applied for harvesting solar radiation may potentially solve the sticky problems of the narrow excitation bandwidth and the low excitation efficiency in rare earth ions doped down-conversion materials

[en] In order to develop promising materials for the Er³⁺-doped fiber amplifier, transparent glass ceramics containing hexagonal CeF₃ nanocrystals were prepared by melt-quenching and subsequent heating. The obvious Stark splitting in the absorption and emission spectra, the intensification of the 1.53 μm emission, and the prolongation of the Er³⁺:⁴I_13/2 decay lifetime demonstrated the partition of Er³⁺ ions into the CeF₃ nanocrystals. Evidently, the efficient cross-relaxation between Ce³⁺ and Er³⁺, i.e., Er³⁺:⁴I_11/2+Ce³⁺:²F_5/2→Er³⁺:⁴I_13/2Ce³⁺:²F_7/2 led to the quenching of the upconversion and the enhancing of the desired Er³⁺ 1.53 μm emission. Based on the emission and absorption spectra, it was further calculated that the glass ceramic possesses broad bandwidth as that of the ZBLAN glass, and large emission cross-section close to the silicate glass, for the 1.53 μm emission.

[en] In this communication, a thermolysis route is developed to synthesize novel Cu_1.94S–ZnS–Cu_1.94S nanoheterostructures with interesting sandwich-like architectures, taking Cu_1.94S nanoplates as precursors. Evidently, the trimeric nanostructure is formed by a three-stage process, which includes the Zn-oleate induced assembling of Cu_1.94S nanoplate couples, the heteronucleation and growth of a ZnS layer between two Cu_1.94S plates dominated by interfacial diffusion, and the catalyst assisted axial growth of ZnS nanorod following the solution–liquid–solid mechanism. With epitaxial growth of ZnS nanocrystal between two Cu_1.94S nanoplates, the localized surface plasmon resonance frequency of Cu_1.94S shifts from 1875 to 1323 nm, indicating that this new material is potentially applicable as a light absorbing agent in laser photothermal therapy. The reported growth mechanism may provide new strategies for designing and fabricating various technologically important polymeric nanoheterostructures. (paper)