A novel ternary sepiolite/Cu2O/Cu (SCC) nanocomposite was successfully synthesized by a facile one-pot method. The Cu2O/Cu nanoparticles in the SCC nanocomposite are well dispersed on the sepiolite ...surface. It exhibited enhanced photocatalytic performance in the degradation of congo red (CR), remarkably superior to that of Cu2O or Cu2O/Cu nanoparticles. Elemental copper in the SCC serves as a good electron acceptor to promote the transfer of photo-generated electrons in Cu2O and suppress the recombination of the photo-generated electrons and holes of the composite. The enhanced photocatalytic efficiency is attributed to the synergistic effect of sepiolite and Cu2O/Cu. This type of SCC nanocomposites is a promising candidate as photocatalytic material for environmental protection.
Red emitting Ba2Si(5-x)AlxN(8-x)Ox:Eu2+ phosphors were successfully produced by high-temperature solid state reaction method and their luminescence properties were experimentally measured. The ...analysis of the experimental results suggests that the partial substitution of Al-O for Si-N in the host lattice improves the photoluminescence properties and the thermal stability of the produced phosphors. The phosphors exhibited a broad red emission band between 500 and 750 nm. A red shift of emission peak from 588 to 624 nm was recorded with the increase of Al-O content, attributed to the enhancement of stokes shift. The excitation spectrum of the produced phosphors ranged between 200 and 600 nm, covering the UV and the blue region, and suggesting these materials as potentially suitable for use as conversion phosphors for white LED applications in the field of solid state lighting.
•Partial substitution of Al-O for Si-N improves the PL properties and the thermal stability.•A red shift of emission peak from 588 to 624 nm was recorded with the increase of Al-O content.•The red shift in the emission spectra attributed to the enhancement of stokes shift due to expansion of host lattice.•The PLE spectra of the produced phosphors ranged between 200 and 600 nm, covering the UV and the blue region.
Pure BaMgSiO4:Eu2+ phosphor, prepared by a solid state reaction method under N2 atmosphere, exhibited a strong green emission at 500 nm and a weak emission at 405 nm. Heat treatment under NH3 ...atmosphere causes changes in the PL intensity: the green emission at 500 nm gradually decreases and completely disappears after heat treatment for 3 h, whereas a new blue emission peak, centered at 445 nm, appears and becomes very strong. The results of the analyses with electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) spectroscopy suggest that the heat treatment causes the generation of a large amount of oxygen vacancies. This resulted in the aforementioned color changes of the BaMgSiO4:Eu phosphor, which are confirmed by the results of DFT+U calculations. In particular, these calculations showed that Eu prefers to occupy Ba(3) sites, which are six coordinated to oxygen atoms. The emission at 500 nm was attributed to the 4f–5d transition energy of Eu in Ba(3) site, calculated as 2.54 eV. It was also shown that Eu 4f energy level decreases when oxygen is removed from the oxygen position adjacent to Eu, which results in a larger Eu 4f–5d transition energy and shorter wavelengths of emission peaks.
Phosphors of CaLa4Si3O13 singly- and co-doped with Ce3+ and Tb3+, which are suitable for application in white LEDs, were successfully produced by using a high temperature solid state reaction method. ...Their apatite crystalline structure as well as their photoluminescent properties both at room temperature and at higher temperatures (up to 150 °C) were experimentally determined, which also allowed the determination of the energy transfer efficiency and mechanism in the host lattice from the sensitizer Ce3+ ions to the activator Tb3+ ions. The excitation spectra of the doped phosphors exhibited an intense, broad band from 200 to 420 nm, which is a good match for the UV and near-UV chip (350–420 nm). Under excitation with UV light, two distinct luminescence bands were recorded; a blue one centered at 433 nm, which is typical for Ce3+ emission, and a green one, which peaks at 552 nm, originated from 5D4 → 7F5 transition in Tb3+.
•Both Ce3+ and Tb3+ ions occupy La3+ sites in CaLa4Si3O13 host.•The emission color shift from blue to green region in Ce3+/Tb3+ co – doped CaLa4Si3O13 phosphors.•The energy transfer efficiency is increase upto 93% with the increasing of Tb3+ concentration.•Energy transfer mechanism illustrate that dipole-dipole energy transfer are dominant from Ce3+ to Tb3+ ion.•The remaining intensity of green emission of Ce3+/Tb3+ co-doped CaLa4Si3O13 phosphors is 70% at 150 °C.
Developing an economical, durable, and efficient electrode that performs well at high current densities and is capable of satisfying large‐scale electrochemical hydrogen production is highly ...demanded. A self‐supported electrocatalytic “Pt‐like” WC porous electrode with open finger‐like holes is produced through industrial processes, and a tightly bonded nitrogen‐doped WC/W (WC‐N/W) heterostructure is formed in situ on the WC grains. The obtained WC‐N/W electrode manifests excellent durability and stability under multi‐step current density in the range of 30–1000 mA cm−2 for more than 220 h in both acidic and alkaline media. Although WC is three orders of magnitude cheaper than Pt, the produced electrode demonstrates comparable hydrogen evolution reaction performance to the Pt electrode at high current density. Density functional theory calculations attribute its superior performance to the electrode structure and the modulated electronic structure at the WC‐N/W interface.
Well established industrial processes are employed to produce self‐supported electrocatalytic WC porous electrode, which features open finger‐like holes and tightly bonded nitrogen‐doped WC/W heterostructure. The electrode manifests excellent stability under multi‐step current density in the range of 30–1000 mA cm−2 for more than 220 h in acidic and alkaline media.
The luminance degradation of BaMgAl10O17:Eu2+(BAM) caused by baking at 600°C was studied. The dissolution of Si–N into BAM lattice lead to only a reduction in the lattice parameters. Under UV ...excitation, the Si–N codoping enhanced the luminescent intensity by a factor of 110% for the as‐received phosphors and by a factor of 122% for phosphors baked at 600°C for 1 h. This could be attributed to the stable local structure surrounding the Eu2+ ions and the lower electronegativity of nitrogen. The proposed method is expected to be potentially applicable to other aluminate phosphors with higher stability and photoluminescence.
Oxynitride phosphor powders comprising of CaSi2O2N2 doped with Tb3+ were successfully synthesized using a high-temperature solid-state reaction method. The experimentally determined photoluminescence ...(PL) properties of the produced phosphors meet the requirements of 2D/3D plasma display panels (PDPs). In particular, under the excitation of vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation, emission peaks corresponding to the 5D3→7FJ (J=6, 5, 4, 3) and 5D4→7FJ (J=6, 5, 4, 3) transitions of Tb3+ ions were recorded. Monitoring the 5D4→7F5 emission of Tb3+ at 545nm, the excitation bands were assigned to the host-related absorption as well as the 4f–5d (fd) and the 4f–4f (ff) transitions of Tb3+. The produced phosphors can be efficiently excited at 147nm, and have an adequately short decay time (τ1/10=1.14ms).
► Tb3+-doped CaSi2O2N2 was proved to be a candidate for plasma display panels (PDPs). ► PL and PLE spectra from VUV to visible range of the phosphor were analyzed. ► The phosphor has an adequately short decay time that is necessary for 3D displays.
Τhe photocatalytic activity in the range of visible light wavelengths and the thermal stability of the structure were significantly enhanced in Si, N co-doped nano-sized TiO₂, and synthesized through ...high-energy mechanical milling of TiO₂ and SiO₂ powders, which was followed by calcination at 600 °C in an ammonia atmosphere. High-energy mechanical milling had a pronounced effect on the mixing and the reaction between the starting powders and greatly favored the transformation of the resultant powder mixture into an amorphous phase that contained a large number of evenly-dispersed nanocrystalline TiO₂ particles as anatase seeds. The experimental results suggest that the elements were homogeneously dispersed at an atomic level in this amorphous phase. After calcination, most of the amorphous phase was crystallized, which resulted in a unique nano-sized crystalline-core/disordered-shell morphology. This novel experimental process is simple, template-free, and provides features of high reproducibility in large-scale industrial production.
Highly efficient Sr2Si5N8:Eu2+ red emitting phosphor was successfully synthesized by a cost-effective direct silicon nitridation and gas-reduction method. The effects of synthesis parameters, ...including reaction temperature, heating rate and gas species, on the crystal structure and photoluminescence of the prepared phosphors were studied. Single-phase Sr2Si5N8:Eu2+ phosphor was obtained at 1500 °C with a heating rate of 300 °C/h under NH3-1 vol.%CH4 atmosphere using starting silicon and oxide powders. Silicon powder and high heating rate favored the achievement of the pure Sr2Si5N8 phase. Under near-UV to blue light excitation, the obtained Sr2Si5N8:Eu2+ phosphor showed a board red emission band centered at about 625 nm, which agreed well with the phosphors prepared by the conventional solid-state reaction. The possible reaction mechanism was also proposed based on the experimental observations.
X-ray diffraction patterns of the phosphors calcined at 1200–1600 °C with the heating rate of 300 °C/h in an NH3-1.0 vol.%CH4 atmosphere
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