4 research outputs found
Giant Enhancement of Upconversion Fluorescence of NaYF<sub>4</sub>:Yb<sup>3+</sup>,Tm<sup>3+</sup> Nanocrystals with Resonant Waveguide Grating Substrate
By
embedding NaYF<sub>4</sub>:Yb<sup>3+</sup>,Tm<sup>3+</sup> nanocrystals
into the top cladding layer of a resonant waveguide grating structure,
we demonstrate that the upconversion fluorescence of Tm<sup>3+</sup> ions can be greatly enhanced, by a factor of up to 10<sup>4</sup>. The resonant waveguide grating structure consists of an SU8 bottom
layer with sinusoidal grating morphology coated with a thin TiO<sub>2</sub> waveguide layer and then covered with a polyÂ(methyl methacrylate)
cladding layer doped with NaYF<sub>4</sub>:Yb<sup>3+</sup>,Tm<sup>3+</sup> nanocrystals. The giant enhancement of the upconversion
fluorescence is achieved first by coupling the excitation light with
a guided mode of the resonant waveguide grating structure and then
the fluorescent light with a second guided mode. Our numerical simulation
results obtained by rigorous coupled-wave analysis indicate that the
electric field of the incident light is strongly enhanced near the
interface of the TiO<sub>2</sub> layer and the polyÂ(methyl methacrylate)
layer at guided mode resonance, and this is the major effect of the
observed enhancement of the upconversion fluorescence of the nanocrystals.
The resonance between the fluorescent emission and the waveguide structure
further enhances the intensities of the fluorescent signal. We also
find that the lifetime of upconversion fluorescence at 480 nm wavelength
from the rare-earth nanocrystals is reduced about 1.34-fold when both
excitation and extraction resonance occurs in the waveguide structure
Macroscopic, Freestanding, and Tubular Graphene Architectures Fabricated <i>via</i> Thermal Annealing
Manipulation of individual graphene sheets/films into specific architectures at macroscopic scales is crucially important for practical uses of graphene. We present herein a versatile and robust method based on annealing of solid carbon precursors on nickel templates and thermo-assisted removal of poly(methyl methacrylate) under low vacuum of ∼0.6 Pa for fabrication of macroscopic, freestanding, and tubular graphene (TG) architectures. Specifically, the TG architectures can be obtained as individual and woven tubes with a diameter of ∼50 μm, a wall thickness in the range of 2.1–2.9 nm, a density of ∼1.53 mg·cm<sup>–3</sup>, a thermal stability up to 600 °C in air, an electrical conductivity of ∼1.48 × 10<sup>6</sup> S·m<sup>–1</sup>, and field emission current densities on the order of 10<sup>4</sup> A·cm<sup>–2</sup> at low applied electrical fields of 0.6–0.7 V·μm<sup>–1</sup>. These properties show great promise for applications in flexible and lightweight electronics, electron guns, or X-ray tube sources
Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup
We
report a versatile strategy to exploit parafilm waste as a carbon
precursor for fabrication of freestanding, hollow few-layer graphene
fiber mesh (HFGM) structures without use of any gaseous carriers/promoters
via an annealing route. The freestanding HFGMs possess good mechanical
flexibility, tailorable transparency, and high electrical conductivity,
consequently qualifying them as promising electrochemical electrodes.
Because of the hollow spaces, electrolyte ions can easily access into
and contact with interior surfaces of the graphene fibers, accordingly
increasing electrode/electrolyte interfacial area. As expected, solid-state
supercapacitors based on the HFGMs exhibit a considerable enhancement
in specific capacitance (20–30 fold) as compared to those employing
chemical vapor deposition compact graphene films. Moreover, the parafilm
waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer
graphene composite meshes with superior electrochemical performance,
outstanding superhydrophobic property, good self-cleaning ability,
and great promise for oil spill cleanup
Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup
We
report a versatile strategy to exploit parafilm waste as a carbon
precursor for fabrication of freestanding, hollow few-layer graphene
fiber mesh (HFGM) structures without use of any gaseous carriers/promoters
via an annealing route. The freestanding HFGMs possess good mechanical
flexibility, tailorable transparency, and high electrical conductivity,
consequently qualifying them as promising electrochemical electrodes.
Because of the hollow spaces, electrolyte ions can easily access into
and contact with interior surfaces of the graphene fibers, accordingly
increasing electrode/electrolyte interfacial area. As expected, solid-state
supercapacitors based on the HFGMs exhibit a considerable enhancement
in specific capacitance (20–30 fold) as compared to those employing
chemical vapor deposition compact graphene films. Moreover, the parafilm
waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer
graphene composite meshes with superior electrochemical performance,
outstanding superhydrophobic property, good self-cleaning ability,
and great promise for oil spill cleanup