Spin-dependent Andreev reflection tunneling through a quantum dot with intradot spin-flip scattering

We study Andreev reflection (AR) tunneling through a quantum dot (QD) connected to a ferromagnet and a superconductor, in which the intradot spin-flip interaction is included. By using the nonequibrium-Green-function method, the formula of the linear AR conductance is derived at zero temperature. It is found that competition between the intradot spin-flip scattering and the tunneling coupling to the leads dominantes resonant behaviours of the AR conductance versus the gate voltage.A weak spin-flip scattering leads to a single peak resonance.However, with the spin-flip scattering strength increasing, the AR conductance will develop into a double peak resonannce implying a novel structure in the tunneling spectrum of the AR conductance. Besides, the effect of the spin-dependent tunneling couplings, the matching of Fermi velocity, and the spin polarization of the ferromagnet on the AR conductance is eximined in detail.Comment: 14 pages, 4 figure

Novel blue-emitting KBaGdSi2O7:Eu2+ phosphor used for near-UV white-light LED

Novel blue-emitting KBaGdSi2O7:Eu2+ phosphors were designed and synthesized through solid-state reaction method. The structural properties, concentration, and temperature-dependent luminescence behaviors of these phosphors were investigated in detail in this paper. Studies revealed that KBaGdSi2O7:Eu2+ phosphors have an intense absorption in the broad wavelength ranging from 250 to 400 nm that is suitable for the commercial near-UV LED, and give out intense blue light peaked at 475 nm with a full-width half-maximum of 75 nm. The crystallographic information of KBaGdSi2O7 phase is revealed from XRD pattern by Rietveld refinement. Band gap is derived to be 3.93 eV through diffuse reflection spectra through Kubelka Munk function. The concentration quenching mechanism is identified as the dipole–dipole interaction. Moreover, the thermal quenching experiment was also conducted and the activation energy is calculated as 0.3069 eV, which indicates this novel KBaGdSi2O7:Eu2+ phosphor has good thermal stability. These properties exhibit its potential commercial application for near-UV white-light LEDs (w-LEDs)