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Wang F.,Chongqing University of Technology | Wang F.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Xu E.-M.,Nanjing University of Posts and Telecommunications
Optics Communications | Year: 2013

We demonstrated a simple scheme to generate ultra wideband (UWB) doublet pulses by inputting a dark return-to-zero (RZ) signal into a fiber delay interferometer (FDI). An 0.625-Gbit/s dark-RZ pulse train where the pulse width is 120 ps was inputted into a FDI where the free spectral range (FSR) is 0.16 nm (∼20 GHz, according time delay is ∼50 ps) and the extinction ratio (ER) is 9 dB, and the phase difference of the two fiber arms was changed and controlled by adjusting the operation temperature of the FDI, by do so, UWB doublet pulses were directly generated at an output port of the FDI. The system parameter effects on the output UWB pulses were discussed. Moreover, we also numerically demonstrated that the UWB quadruplet pulses can be generated in the same set by optimizing system parameters. This scheme has some distinct advantages including easy integration, convenient tuning, good stability, and so on. Presented method also accords with the general features in future applied UWB-Over-Fiber communication system, such as, single optical source input, simple configuration and passive device. © 2013 Elsevier B.V.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Feng W.-L.,CAS International Center for Materials Physics | Jin Y.,Chongqing University of Technology | And 3 more authors.
Journal of Luminescence | Year: 2013

Ba1-xMoO4:xEu3+ red phosphors were synthesized by the co-precipitation method with NH4HCO 3-NH3·H2O system as the precipitating agent. X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectra were used to characterize the structures and luminescent properties of the phosphors. The results showed that introduction of Eu did not change the crystal structure and morphology of BaMoO 4:Eu3+ phosphors. In addition, the influence of different contents of dopant Eu3+ for the luminescent properties of red phosphors Ba1-xMoO4:xEu3+ was analyzed. Photoluminescence spectra showed a red emission around 612 nm with 395 and 465 nm excitations, which matches the output wavelength of ultraviolet and blue LED chips. The optimal doping concentration of the red phosphors Ba 1-xMoO4:xEu3+ was 30 mol%. © 2012 Elsevier B.V. All rights reserved.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Feng W.-L.,CAS International Center for Materials Physics | Zheng W.-C.,Sichuan University | Zheng W.-C.,CAS International Center for Materials Physics
Molecular Physics | Year: 2014

The spin-Hamiltonian parameters (g factors gi and hyperfine structure constants Aii, where i = x, y, z) of the rhombic Cu 2+ centres in the CuGaSe2 crystal are determined from the high-order perturbation formulae based on the cluster approach (sometimes also called two-spin-orbit parameter model). In the studies, some parameters in the analysis of g factors for the same centre within the tetragonal symmetry approximation in the previous paper are used, and the parameter due to the perturbation of rhombic crystal field caused by a charge compensator at, e.g., [110] direction are considered. As the result of a fitting process, the determined spin-Hamiltonian parameters are in reasonable agreement with the experimental values. The results are discussed. © 2014 © 2013 Taylor & Francis.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,CAS International Center for Materials Physics | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Wang K.,Chongqing University of Technology | And 3 more authors.
Journal of Physics and Chemistry of Solids | Year: 2014

The spin-Hamiltonian (or EPR) parameters of tetragonal Cu2+ octahedral centers in ZnCdO nanopowders are calculated from the high-order perturbation formulas based on the cluster approach. In these formulas, the contributions to spin-Hamiltonian parameters due to the admixture between the d orbitals of dn ion and the p orbitals of ligand ions via covalence effect are considered. The crystal field parameters are calculated from the superposition model and so the optical absorption bands (related to the crystal field energy levels) and local structure of Cu2+ octahedral centers in ZnCdO nanopowder are also studied. The calculated spin-Hamiltonian parameters and optical absorption bands are in reasonable agreement with the experimental values. The tetragonal elongation ΔR (=R//-R ⊥) of Cu2+ octahedron in ZnCdO nanopowder due to Jahn-Teller effect is acquired from the calculations. The results are discussed. © 2014 Elsevier Ltd.


Feng W.L.,Chongqing University of Technology | Feng W.L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Zhao M.F.,CAS International Center for Materials Physics | Li T.,Chongqing University of Technology | And 2 more authors.
Acta Physica Polonica A | Year: 2012

Electron spin resonance spectral parameters of V4+ ions in vanadate-lithium-borate glasses have been calculated by the crystal-field theory. The theoretical results are g∥ = 1.940, g⊥ = 1.983 and A∥ = -175 × 10-4 cm-1, A⊥ = -65 × 10 -4 cm-1 which are good agreement with the experimental values (g∥ = 1.939(3), g⊥ = 1.998(3) and A∥ = (170.6-176:4) × 10-4 cm-1, A⊥ = (61.3-71.4) × 10-4 cm-1). In addition, the bond lengths of the local lattice structure are, respectively, R∥ = 1.5 Å and R⊥ = 1.95 Å which have been shown to have a compressed tetrahedral geometry along the C4 axis.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Feng W.-L.,CAS International Center for Materials Physics
Philosophical Magazine Letters | Year: 2012

The Raman spectra and electronic spin resonance (ESR) parameters (spin-Hamiltonian parameter g factors, zero-field splitting parameter D, and hyperfine structure constant A) for the trigonal V 3+ centers in salt guanidinium vanadium sulfate hexahydrate (GVSH) are calculated from the complete diagonalization (of energy matrix) method. The theoretical results are in agreement with the experimental findings and the trigonal crystal-field parameters are determined. The difficulty in explaining ESR parameters of V 3+ in GVSH is removed. © 2012 Taylor & Francis.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,CAS International Center for Materials Physics | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology
Physica B: Condensed Matter | Year: 2012

The optical absorption spectra and electronic spin resonance parameters (ESR g factors g||, g⊥ and hyperfine structure constants A||, A⊥) for Cu2+ in shattuckite crystal are calculated from the two spin-orbital coupling parameters model, high-order perturbation formulas and complete diagonalization (of energy matrix) method (CDM) of 3d9 ion in tetragonal symmetry. The calculated results are in good agreement with the observed values. Since the ESR parameters are sensitive to the local structure of a paramagnetic impurity center, the defect structure of Cu2+ center in shattuckite crystal is estimated. The results are discussed. © 2012 Elsevier B.V. All rights reserved.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Feng W.-L.,CAS International Center for Materials Physics
Journal of Magnetism and Magnetic Materials | Year: 2012

The electron paramagnetic resonance (EPR) spectral data (the g factors and hyperfine structure constants) and d-d transition spectra for the tetragonal Mo 5 centre in [Mo 6O 19][N(C 4H 9) 4] 3 salt are theoretically investigated from the complete diagonalization method (CDM) for a 4d 1 ion in tetragonally compressed octahedron. The theoretical results are in good agreement with the experimental data. The dependency of the g factors of the ground state on the R ∥(MoO bond length) has been studied. It is shown that the g factors varied with the R ∥ approximately in a linear way. © 2012 Elsevier B.V. All rights reserved.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,CAS International Center for Materials Physics | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Xue J.-Y.,Chongqing University of Technology
Physica B: Condensed Matter | Year: 2012

In this work, the complete matrix of optical spectral levels in trigonal symmetry of 3d 2 (3d 8) ions are established on basis of strong field coupling mechanism by using two spin-orbit coupling parameters model. The contribution of the spin-orbit coupling of ligand to the optical spectra has been included in these formulas. As an application, the optical spectra of Cr 4 in Y 2Ti 2O 7 and Y 2Sn 2O 7 have been studied by the complete diagonalization (energy matrix) method. The covalent effect has been studied and the difficulty about Dq parameter in explanation of optical spectra of Cr-doped Y 2Ti 2O 7 and Y 2Sn 2O 7 is removed. The theoretical results are in good agreement with observed data. © 2012 Elsevier B.V. All rights reserved.


Feng W.-L.,Chongqing University of Technology | Feng W.-L.,CAS International Center for Materials Physics | Feng W.-L.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology | Xue J.-Y.,Chongqing University of Technology | Xue J.-Y.,Chongqing Key Laboratory of Time Grating Sensing and Advanced Testing Technology
Journal of Non-Crystalline Solids | Year: 2014

The high-order perturbation formulas based on the two-mechanism model are used to calculate the spin-Hamiltonian parameters (g factors g//, g∥ and hyperfine structure constants A//, A ∥) of the tetragonal Mo5 + centers in phosphate glasses xMoO2·(100 - x)[2P2O5· Na2O]. In the calculations, not only the crystal-field (CF) mechanism concerning CF excited states in the widely-applied CF theory, but also the charge-transfer (CT) mechanism concerning CT excited states (which is often omitted) is taken into account. The calculated results are close to the experimental values. The calculations show that the contributions Δg i CT (= gi - ge, where ge ≈ 2.0023) and Ai (2)CT due to CT mechanism in sign are contrary to the corresponding Δgi CF and A i (2)CF due to CF mechanism, and the values of relative importance |QCT/QCF| of CT mechanism are about 19%, 17%, 8% and 13% for Q = Δg//, Δg∥, A // (2) and A∥ (2). It appears that in the complete and exact calculations of spin-Hamiltonian parameters for the high valence state dn ions (e.g., Mo5 + considered here) in crystals, one should take into account the two (CF and CT)-mechanism model. © 2013 Elsevier B.V.

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