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Development of UVB Radiation-Emitting Gd3+-Doped Na3YSi2O7 Host Material
摘要： In this work, we synthesized and characterized a narrow-band, ultraviolet-emitting Na3YSi2O7:Gd3+ material. A series of Na3Y1-xSi2O7:Gdx (x = 0.01 ≤ x ≤ 0.11) samples were synthesized using a sol–gel process. X-ray diffraction patterns of all the samples were found to be similar to the hexagonal Na3YSi2O7 phase. Morphology and functional group analysis were performed using scanning electron microscopy and Fourier transform infrared spectroscopy. The effects of gadolinium concentration on the luminescence intensity of the Na3YSi2O7:Gd3+ samples were investigated. The developed sample exhibited an ultraviolet emission peaking at 313 nm under 273-nm excitation. The dominant band at 313 nm was attributed to 6P7/2 → 8S7/2 transition of Gd3+ ions. The electron paramagnetic resonance (EPR) studies revealed the presence of Gd3+ ions in octahedral Y3+ sites in the host lattice.
关键词： EPR,Na3YSi2O7,photoluminescence,XRD,Gd3+ ions,Sol–gel
更新于2025-09-23 15:22:29
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Synthesis of broad yellow phosphors by co-doping and realization of high quality of white light
摘要： In order to obtain high quality white light, we synthesized yellow phosphors by doping europium and other lanthanoids such as holmium and lutetium. We successfully obtained yellow phosphors with green emissions with a wavelength of 510 nm for Li2SrSiO4 by co-doping europium and holmium. Unlike single doping of europium, a lower reduction temperature seemed to be preferable. When we simulated the chromaticity of white light at 5000 K, achieved by mixing blue light, which was used for excitation, and this phosphor, it resulted in better quality than commercially available products.
关键词： europium,sol-gel method,white light,Co-doping
更新于2025-09-23 15:22:29
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Synthesis and Characterization of ZnO-ZrO <sub/>2</sub> Nanocomposites for Photocatalytic Degradation and Mineralization of Phenol
摘要： ZnO-ZrO2 nanocomposites using zinc (II) acetylacetonate and different ZnO contents (13, 25, 50, and 75% mol) were synthesized through sol-gel method. The synthesis process was strongly related to nanocomposite properties especially on their structural composition. The obtained ZnO-ZrO2 nanomaterials presented tetragonal crystalline structure for zirconia whereas hexagonal one was formed in ZnO. Raman spectroscopy and XRD patterns confirmed the formation of tetragonal zirconia whereas inhibition of monoclinic structure was observed. Addition of ZnO affected the pore size distribution of the composite, and the measured specific surface areas were from 10 m2/g (for pure ZnO) to 46 m2/g (pristine ZrO2). Eg values of ZrO2 were modified by ZnO addition, since calculated values using Kubelka-Munk's function varied from 4.73 to 3.76 eV. The morphology and size of the nanomaterials investigated by electron microscopy showed formation of nanorods for ZnO with sizes ranging from 50 nm to 300 nm while zirconia was formed by smaller particles (less than 50 nm). The main advantage of using the nanocomposite for photocatalytic degradation of phenol was the mineralization degree, since 75ZnO-ZrO2 nanocomposite surpassed mineralization reached by pure ZnO and also inhibited formation of undesirable intermediates.
关键词： sol-gel method,UV-A irradiation,phenol mineralization,photocatalytic degradation,ZnO-ZrO2 nanocomposites
更新于2025-09-23 15:22:29
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Enhanced UV emission of TiO <sub/>2</sub> –ZnO nanocomposite films synthesized by simplified sol–gel dip-coating method
摘要： TiO2–ZnO composite film was regarded as a promising candidate for UV emitter devices. For exploring a lower cost and convenient preparation method for highly efficient UV-emission TiO2–ZnO composite film, we used a simplified method in which mixing ZnO sol and TiO2 sol directly to prepare TiO2–ZnO nanocomposite films with a varied atomic ratio of Zn/(Ti + Zn) (TiO2, Z20, Z40, Z60, Z80, ZnO) on glass substrates and discussed its optical properties for the first time in this study. The photoluminescence (PL) spectra indicated that the UV emission of the composite films was greatly enhanced compared with that showed by single-phase TiO2 or ZnO film. In particular, the UV emission intensity of Z60 composite film was enhanced by a factor of 10 compared to that of single-phase ZnO or TiO2. The enhanced PL intensity of the composite films could be attributed to fluorescence resonance energy transfer (FRET).
关键词： TiO2–ZnO Nanocomposite Films,Optical Property,Simplified Sol–Gel Method,FRET
更新于2025-09-23 15:22:29
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Bulk Photodriven CO <sub/>2</sub> Conversion through TiO <sub/>2</sub> @Si(HIPE) Monolithic Macrocellular Foams
摘要： Operating photo-induced reactions exclusively on catalyst surfaces while not exploiting the full catalyst volume generates a major footprint penalty for the photocatalytic reactor and leads to an inefficient use of the catalytic material. Photonic investigations clearly show that the solid foams have a strongly multi-diffusive character, with photons being significantly trapped within the sample cores while addressing a photon mean free path lt = 20.1 ± 1.3 μm. This 3D process both greatly limits back-reactions and promotes outstanding selectivity toward methane (around 80%) generation, and even ethane (around 18%) through C-C coupling reaction, with residual carbon monoxide and dihydrogen contents (around 2%). Silica–titania TiO2@Si(HIPE) self-standing macrocellular catalysts lead to optimal efficient thicknesses up to 20 times those of powders, thereby enhancing the way for real 3D-photodriven catalytic processes above the millimeter scale and up to a 6 mm thickness. A rather simple Langmuir–Hinshelwood based kinetic model is proposed which highlights the strong dependence of photocatalytic reaction rates on light scattering and the crucial role on oxidation back-reactions. In addition, a strong correlation between light attenuation coefficient and photon mean free path and median pore aperture diameter is demonstrated, offering thus a tool for photocatalytic behavior prediction.
关键词： heterogeneous catalysis,CO2 photoreduction,sol–gel process,porous materials,integrative chemistry
更新于2025-09-23 15:22:29
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Fabrication and Photoluminescence Properties of Monodispersed SiO2@SrAl2Si2O8:Eu2+ Core-Shell Submicron Spheres
摘要： Nanocrystalline SrAl2Si2O8:Eu2+ phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted monodispersed SiO2@SrAl2Si2O8:Eu2+ core-shell submicron spherical phosphors were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectra. The XRD results demonstrated that the SrAl2Si2O8:Eu2+ layers began to crystallize on the SiO2 spheres at 900 °C and the crystallinity increased with raising the annealing temperature. The obtained monodispersed core-shell spherical phosphors have perfect spherical shape with narrow size distribution (average size 500 nm). The Eu2+ shows a strong photoluminescence (dominated by 4f65d1 → 4f7 red emission at 390 nm) due to an efficient energy transfer from vanadate groups to Eu2+. The photoluminescence intensity of Eu2+ increases with raising the annealing temperature.
关键词： Nanostructures,Sol-gel processes,Optical properties,X-ray diffraction,Phosphers
更新于2025-09-23 15:22:29
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A comparative study of Sr-doped LaMnO <sub/>3</sub> synthesised via solid-state reaction and sol–gel methods
摘要： This work deals with the synthesis of hole-doped La1-xSrxMnO3 (x = 0.25 and 0.33) perovskite via two different ways, namely a solid-state reaction method and a sol–gel process. Various properties of the samples have been investigated and compared by means of different techniques, namely X-ray diffraction (XRD), temperature-dependent resistivity measurements in the temperature range 25–300 K using a closed cycle refrigerator and vibrating sample magnetometry (VSM). All samples have orthorhombic crystal symmetry and an irregular variation in unit-cell volume with increase in Sr content. The average crystallite size was determined from the XRD data and found to lie in the range 19–22 nm. Metal–insulator transitions (MIT) were observed in all the samples via low-temperature electrical characterisations. The magnetic measurements confirm that the magnetisation does not saturate for the 25% Sr doped samples up to the available field of 10 kOe. The magnetic response also supports the interpretation of XRD and resistivity data. The obtained results are explained on the basis of double-exchange and super-exchange mechanisms.
关键词： CMR,manganites,metal to insulator transition (MIT),sol–gel method,Solid-state reaction
更新于2025-09-23 15:22:29
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PZT/PZT and PZT/BiT Composite Piezo-Sensors in Aerospace SHM Applications: Photochemical Metal Organic + Infiltration Deposition and Characterization
摘要： The composition of fine-ground lead zirconate-titanate powder Pb(Zr0.52Ti0.48)O3, suspended in PZT and bismuth titanate (BiT) solutions, is deposited on the curved surface of IN718 and IN738 nickel-based super alloy substrates up to 100 μm thickness. Photochemical metal organic and infiltration techniques are implemented to produce smooth, semi-dense, and crack-free random orientated thick piezoelectric films as piezo-sensors, free of any dopants or thickening polymers. Every single layer of the deposited films is heated at 200 °C with 10 wt.% excess PbO, irradiated by ultraviolet lamp (365 nm, 6 watt) for 10 min, pyrolyzed at 400 °C, and subsequently annealed at 700 °C for one hour. This process is repeated successively until reaching the desired thickness. Au and Pt thin films are deposited as the bottom and top electrodes using evaporation and sputtering methods, respectively. PZT/PZT and PZT/BiT composite films are then characterized and compared to similar PZT and BiT thick films deposited on the similar substrates. The effect of the composition and deposition process is also investigated on the crystalline phase development and microstructure morphology as well as the dielectric, ferroelectric, and piezoelectric properties of piezo-films. The maximum remnant polarization of Pr = 22.37 ± 0.01, 30.01 ± 0.01 μC/cm2, the permittivity of εr = 298 ± 3, 566 ± 5, and piezoelectric charge coefficient of d33 = 126, 148 m/V were measured versus the minimum coercive field of Ec = 50, 20 kV/cm for the PZT/PZT and PZT/BiT thick films, respectively. The thick film piezo-sensors are developed to be potentially used at frequency bandwidth of 1–5 MHz for rotary structural health monitoring and also in other industrial or medical applications as a transceiver.
关键词： piezoelectric sensor,structural health monitoring,PZT/BiT,composite,characterization,sol-gel PMOD deposition,infiltration,aerospace structure,PZT/PZT,thick film
更新于2025-09-23 15:22:29
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Hydrogen Gas Sensing Characterizations Based on Nanocrystalline SnO<sub>2</sub> Thin Films Grown on SiO<sub>2</sub>/Si and Al<sub>2</sub>O<sub>3</sub> Substrates
摘要： High-quality nanocrystalline (NC) SnO2 thin films were grown on SiO2/Si and Al2O3 substrates using sol–gel spin coating method. The structural properties, surface morphologies and gas sensing properties of the NC SnO2 were investigated. XRD measurements showed a tetragonal rutile structure and the diffraction peaks for NC SnO2 thin films grown on Al2O3 substrates outperformed those of NC SnO2 films grown on SiO2/Si substrates. The surface morphology of the annealed SnO2 thin films at 500 oC appeared as polycrystalline with uniform nanoparticle distribution. Hydrogen (H2) gas sensing performance of the NC SnO2 was examined for H2 concentrations ranging from 150 ppm to 1000 ppm at different temperatures (room temperature, 75 and 125 oC) for over 50 min. The room temperature sensitivities for H2 gas sensors based on NC SnO2 thin films grown on Al2O3 and SiO2/Si substrates was 2570% and 600%, respectively upon exposure to 1000 ppm of H2 gas. While the sensitivity values at 125 oC increased to 9200% and 1950%, respectively.
关键词： Sensing,Room Temperature,Hydrogen,Nanocrystalline SnO2,Thin Films,Sol-Gel
更新于2025-09-23 15:22:29
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Facile Sol-gel Synthesis of Metaloxide Nanoparticles in a Cellulose Paper Template
摘要： Ensembles of free standing particles of titanium, zinc, copper and iron oxides of 6-109 nm in size were sol-gel synthesized with a use of a cellulose paper as a template. The calcination time as short as 60 min at 550°C in air was found to be sufficient for the formation of crystalline single phase TiO2 or ZnO nanoparticles, Cu2O+CuO or Fe2O3+Fe3O4 nanocomposites and to burn out the organic components. The impurities initially present in the cellulose (Сa, Na, Cl) were detected in the synthesized compounds.
关键词： Sol-gel synthesis,Zinc oxide,Nanoparticle,Copper oxides,Cellulose,Iron oxides,Titanium oxide
更新于2025-09-23 15:22:29