A lightweight, flexible, and highly efficient energy management strategy is needed for flexible energy-storage devices to meet a rapidly growing demand. Graphene-based flexible supercapacitors are one of the most promising candidates because of their intriguing features. In this report, we describe the use of freestanding, lightweight (0.75 mg/cm(2)), ultrathin (<200 μm), highly conductive (55 S/cm), and flexible three-dimensional (3D) graphene networks, loaded with MnO(2) by electrodeposition, as the electrodes of a flexible supercapacitor. It was found that the 3D graphene networks showed an ideal supporter for active materials and permitted a large MnO(2) mass loading of 9.8 mg/cm(2) (~92.9% of the mass of the entire electrode), leading to a high area capacitance of 1.42 F/cm(2) at a scan rate of 2 mV/s. With a view to practical applications, we have further optimized the MnO(2) content with respect to the entire electrode and achieved a maximum specific capacitance of 130 F/g. In addition, we have also explored the excellent electrochemical performance of a symmetrical supercapacitor (of weight less than 10 mg and thickness ~0.8 mm) consisting of a sandwich structure of two pieces of 3D graphene/MnO(2) composite network separated by a membrane and encapsulated in polyethylene terephthalate (PET) membranes. This research might provide a method for flexible, lightweight, high-performance, low-cost, and environmentally friendly materials used in energy conversion and storage systems for the effective use of renewable energy.

Uniform red-phosphor spheres (∼60-300 nm in diameter) of Y 2 O 3 :Eu 3+ binary and (Y,Gd) 2 O 3 :Eu 3+ ternary systems exhibiting excellent emission at 610 nm have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The precursor spheres (approximate composition: [(Y 1-x Gd x ) 1-y -Eu y ](OH)CO 3 • 1.3H 2 O, x ) 0-0.5 and y ) 0-0.11) are directly solid solutions, but arising from sequential nucleation each of the spheres has more Gd and especially Eu while having less Y going from the particle surface to the core. Eu 3+ is more effective than Gd 3+ in raising nucleation density, leading to rapidly decreased average size of the precursor particles at a higher Eu 3+ addition. Diminishing the concentration gradients through adequate annealing is identified to be crucial to high luminous intensity of the oxide particles. At the optimal annealing temperature of 1000 °C, cation homogenization is achieved and the oxide particles largely retain their precursor morphologies, yielding dispersed uniform spheres of excellent luminescence. The (Y 1-x -Eu x )O 1.5 phosphor particles exhibit typical red emissions at 610 nm upon UV excitation into the charge transfer band at ∼255 nm, and the quenching concentration of Eu 3+ is found to be ∼5 at. %. Partially replacing Y 3+ with Gd 3+ (up to 50 at. %) while keeping Eu 3+ at the optimal content of 5 at. % linearly improves the 610 nm emission, and the phosphor particles of [(Y 0.5 Gd 0.5 ) 0.95 Eu 0.05 ]O 1.5 exhibit an luminous intensity ∼103% of that of a commercially available Y 2 O 3 :Eu red phosphor. The uniform phosphor spheres obtained in this work are expected to have wide applications in high-resolution display technologies of contemporary interest.

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