Industrial Requirements of Materials for Electrical Double Layer Capacitors: Impact on Current and Future Applications

Rare earth (RE) doped phosphors and their emerging applications: A review

Sr2SiO4:Eu2+ phosphors were synthesized by a conventional solid state reaction method. After a low amount of nitrogen (∼1 mol% of oxygen) was incorporated to modify the local coordination environment of Eu2+, the phosphor showed a single intense broad band emission centered at 625 nm under blue light (453 nm) excitation, and three emission bands (480, 555 and 625 nm) under ultraviolet irradiation. The incorporation of nitrogen was confirmed by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) and absorption spectroscopy. 480 and 555 nm emissions originated from Eu2+ ions occupying the Sr(I) sites and Sr(II) sites in the Sr2SiO4 crystal, respectively, while 625 nm emission originated from the nitrogen coordinated Eu2+ ions. The local coordination structure around Eu2+ ions in the red phosphors was analyzed with the aid of density functional theory based first principles calculations. The analysis showed that nitrogen should preferentially substitute the O5′ sites around Eu2+ in Sr(II) sites, which agreed fairly well with the experimental results from the X-ray absorption fine structure (XAFS) and the electron paramagnetic resonance (EPR) spectra. The electronic structure analysis confirmed the lowered center of gravity of Eu 5d energy states and the broadened Eu 4f energy states, which are due to the tightened coordination environment and the hybridization of the 4f states of Eu and 2p states of nitrogen–oxygen, leading to a red emission. The novel nitrogen modified Sr2SiO4:Eu2+ could serve as a full color phosphor for near-UV LEDs or a red-emitting phosphor for blue LEDs.

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Modification of the coordination environment of Eu2+ in Sr2SiO4:Eu2+ phosphors to achieve full color emission

An efficient charge compensated red phosphor Sr3WO6: K+, Eu3+ – For white LEDs

Investigation of viscoelastic and active corrosion protection properties of inhibitor modified silica nanoparticles/epoxy nanocomposite coatings on carbon steel

Preparation of Sr2Si5N8:Eu2+ for white light-emitting diodes by multi-step heat treatment

For additional use in industry and biomedicine, water-soluble Cu2+-doped ZnS quantum dots (QDs) (ZnS:Cu) were synthesized with thioglycolic acid (TGA) as the stabilizer in aqueous solutions in air. The products were characterized by x-ray diffraction, ultraviolet–visible spectroscopy, transmission electron microscopy, and photoluminescence. The effect of Cu2+ doping concentration and TGA/(Zn+Cu) molar ratio on crystal structures and the luminescent intensity of ZnS:Cu QDs have been investigated. As a result, The as-prepared ZnS:Cu QDs had diameters of 10–12 nm and a sphere monodisperse form that consists of ZnS:Cu nanoparticles of approximately 2 nm. The optimum Cu2+ doping concentration and TGA/(Zn+Cu) molar ratio were obtained when the photoluminescent emission showed a maximum value.

Synthesis and optical property of water-soluble ZnS:Cu quantum dots by use of thioglycolic acid

Polyethylene glycol (PEG) molecules have been grafted onto the surface of nanometer silica intoluenebyusing1,4-phenylene diisocyanate (PPDI) as a coupling agent, and dibutyltion dilaurate (DBTDL) as a catalyst. This process was executed by using a one-step procedure involving a first reaction of PPDI with silica and a subsequent reaction of isocyanate-bound silica with PEG. Optimum grafting conditions of PEG were obtained at the temperature of 80 ℃ for 8 h. Maximum grafting of PEG molecules ratio was 22.6%, and maximum overall grafting ratio was 35%, as determined by TGA.

Grafting of polyethylene glycols onto nanometer silica surface by 1,4-phenylene diisocyanate

For the further application performance, CdS:Mn nanocrystals coated with zinc hydroxide (Zn(OH) 2 ) shells were prepared via wet chemical method. Effect of Zn(OH) 2 shells on optical properties of CdS:Mn nanocrystals was investigated. X-ray diffraction (XRD) measurements showed that the CdS nanocrystals have hexagonal wurtzite structure. The morphology and components of CdS:Mn/Zn(OH) 2 core/shell nanocrystals were successfully measured by transmission electron microscopy (TEM) with energy-dispersive X-ray (EDX). Luminescence properties (intensity and lifetime) of 4 T 1  →  6 A 1 transition of Mn 2+ ions in CdS:Mn/Zn(OH) 2 core/shell nanocrystals were significantly enhanced as compared with those of unpassivated CdS:Mn nanocrystals. This expected result was caused by the effective, robust passivation of CdS surface states with Zn(OH) 2 shells, which consequently suppressed nonradiative recombination transitions.

Optical properties of CdS:Mn nanocrystals surface passivated with zinc hydroxide

Several methods for improving dispersion of carbon nanotubes (CNTs) have been investigated. CNTs modified by acids and hydrogen peroxide (H₂O₂) showed improved dispersion. From SEM micrographs and photos of dispersion, CNTs modified with nitric acid and H₂O₂, showed no agglomeration in solution even standing for 4 months, which means successfully improved dispersion property. TEM micrographs of surface modified single CNT treated with 69% HNO₃ in boiling acid solution as the optimum method were obtained. For confirmation of CNTs’ application to EDLC electrode materials, characteristics of EDLC have been analyzed by cyclic voltammetry curve, specific capacitance of unit cell, electrode discharge curves and AC impedance curve. From the results, it could be confirmed that electrochemical properties of CNTs were enhanced after surface modification with 69% HNO₃ acid treatment.

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Wentao Zhang

Papers

Preparation of Sr2Si5N8:Eu2+ for white light-emitting diodes by multi-step heat treatment

Synthesis and optical property of water-soluble ZnS:Cu quantum dots by use of thioglycolic acid

Grafting of polyethylene glycols onto nanometer silica surface by 1,4-phenylene diisocyanate

Optical properties of CdS:Mn nanocrystals surface passivated with zinc hydroxide

Surface Modification of Multi-walled Carbon Nanotubes for Enhancement of Dispersion and Electrochemical Properties