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The MnO 2 nanoflowers/reduced graphene oxide composite is coated on a nickel foam substrate (denoted as MnO 2 NF/RGO @ Ni foam) via the layer by layer (LBL) self-assembly technology without any polymer additive, following the soft chemical reduction. The layered MnO 2 NF/RGO composite is uniformly anchored on the Ni foam skeleton to form the 3D porous framework, and the interlayers have access to lots of ions channels to improve the electron transfer and diffusion. This special construction of 3D porous structure is beneficial to the enhancement of electrochemical property. The specific capacitance is up to 246 F g −1 under the current density of 0.5 A g −1 . After 1000 cycles, it can retain about 93%, exhibiting excellent cycle stability. The electrochemical impedance spectroscopy measurements confirm that MnO 2 NF/RGO @ Ni foam electrode has lower R ESR and R CT values when compared to MnO 2 @ Ni foam and RGO @ Ni foam. This study opens a new door to the preparation of composite electrodes for high performance supercapacitor. [ABSTRACT FROM AUTHOR]

P2-type layered Na 2/3 Ni 1/4 Mn 3/4 O 2 has been synthesized by a solid-state method and its electrochemical behavior has been investigated as a potential cathode material in aqueous hybrid sodium/lithium ion electrolyte by adopting activated carbon as the counter electrode. The results indicate that the Na + /Li + ratio in aqueous electrolyte has a strong influence on the capacity and cyclic stability of the Na 2/3 Ni 1/4 Mn 3/4 O 2 electrode. Increase on the Li + content leads to a shift of the redox potential towards a high value, which is favorable for the improvement of the working voltage of the layered material as cathode. It is found that the coexistence of Na + and Li + in aqueous electrolyte can improve the cyclic stability for the Na 2/3 Ni 1/4 Mn 3/4 O 2 electrode. A reversible capacity of 54 mAh g −1 was obtained with a high cyclability as the Na + /Li + ratio was 2:2. Furthermore, an aqueous hybrid ion cell was assembled with the as-proposed Na 2/3 Ni 1/4 Mn 3/4 O 2 as cathode and NaTi 2 (PO 4 ) 3 /graphite synthesized in this work as anode in 1 M Na 2 SO 4 /Li 2 SO 4 (mole ratio as 2:2) mixed electrolyte. The cell shows an average discharge voltage at 1.2 V, delivering an energy density of 36 Wh kg −1 at a power density of 16 W kg −1 based on the total mass of the active materials. [ABSTRACT FROM AUTHOR]

Abstract: The reduced graphene oxide (RGO)/NiFe2O4 composite was synthesized by a facile one-pot hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of graphene oxide (GO) and the crystallization of NiFe2O4 crystals happened in a one-step hydrothermal process. The morphology, microstructure and magnetic properties of the composite were detected by means of XRD, XPS, TEM, EDX, TG-DSC and VSM. The maximum R L of the RGO/NiFe2O4 composite is −39.7dB at 9.2GHz with the thickness of 3.0mm, and the absorption bandwidth with the R L below −10dB is up to 5.0GHz (from 12.7 to 17.7GHz) with a thickness of 1.9mm. The introduction of RGO signally enhanced microwave absorption performance of the NiFe2O4 NPs. It is believed that such composite will be applied widely in microwave absorbing area. [Copyright &y& Elsevier]

Abstract: This study presents the luminescent properties of Yb3+/Tm3+ co-dopant ions inside a new host glass based on bismuth germanates. Judd–Ofelt intense parameters, radiative transition rate, radiative lifetime, and branching ratios of Tm3+ in the present glass are calculated based on the absorption spectrum. A strong 1.8μm emission was observed in the Yb3+/Tm3+ co-doped bismuth germanate glass upon the excitation of a conventional 980nm laser diode. Using a spectral overlap model, the micro parameter for direct energy transfer from Yb3+ ions to Tm3+ ions (C DA ) was found to be almost 30 times larger than the back energy transfer from Tm3+ ions to Yb3+ ions (C AD ). The linear dependence of energy transfer probability on the co-dopant concentration exhibits that the energy transfer is assisted by energy migration among donor ions. The large energy transfer efficiency (89%) indicates that the Yb3+/Tm3+ co-doped bismuth germanate glass is a good candidate for the 1.8μm laser. [Copyright &y& Elsevier]

Abstract: A series of novel red emitting phosphors Li6M(La1−x Eu x )2Nb2O12 (M=Ca, Sr, Ba; 0≤x≤0.3) were synthesized by solid state reaction, and their structures and photoluminescence properties were investigated in detail. The excitation spectrum of Li6M(La1−x Eu x )2Nb2O12 revealed two mainly excitation bands at 393nm and 464nm, which match well with the two popular emissions from near-UV and blue LED chips. Upon the 464nm light excitation, Li6MLa2Nb2O12:Eu3+ phosphors exhibit a red emission centered at 608nm, originated from the 5D0–7F2 transition of Eu3+ ions. The Eu3+ surrounding crystal lattice environment in the garnet-based host was changed by altering the c sites element with different radii alkaline earth Ba, Sr, and Ca. The evident photoluminescence enhancement was observed in Li6M(La1−x Eu x )2Nb2O12 phosphors with the decreasing of the c sites ionic radius. The emission intensity of the optimized Li6Ca(La0.8Eu0.2)2Nb2O12 (λ exc=464nm) phosphor is about two times higher than that of Y2O3:Eu3+ (λ exc=467nm) under blue light excitation. In addition, the quenching mechanism and the relationship between the structure and photoluminescence property were also discussed. [Copyright &y& Elsevier]