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1.
Li2O-ZrO2-SiO2: Ho3+ glasses mixed with three interesting d-block elemental oxides, viz., Nb2O5, Ta2O5 and La2O3, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb2O5 and Ta2O5 mixed Li2O-ZrO2-SiO2 glasses (free of Ho3+ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta5+ and Nb5+ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho3+ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio βr and the radiative lifetime τr, for 5S2 emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for 5S2 level of Ho3+ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La2O3 mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho3+ ions.  相似文献   

2.
The controlled synthesis of mesoporous silica and metal oxide nanocomposites with a highly ordered porous structure and large specific surface area for specific applications has been an attractive topic in the field of porous materials. Herein, we introduce a novel method for the fabrication of highly ordered mesoporous structured and large specific surface area Fe2O3/SiO2 nanocomposites, and consider their application in room temperature gas sensors. The mesoporous Fe2O3/SiO2 nanocomposites were synthesised by a two-step method, which combines the hydrothermal growth of Fe2O3 nanoparticles and the microemulsion phase of Brij 56 (C16EO10) surfactant as templates in instantly direct-templating synthesis. This synthesis method enables the fabrication of mesoporous Fe2O3/SiO2 nanocomposites without distortion of the ordered porous structure after calcination at high temperature. The synthesised materials were found to be efficient in a room temperature VOC sensor application, with good recovery.  相似文献   

3.
朱振华  雷明凯 《物理学报》2006,55(9):4956-4961
采用溶胶-凝胶(sol-gel)工艺制备0.1 mol% Er3+掺杂Al2O3体系和SiO2-Al2O3复合体系粉末. 实验结果表明:5 mol%的SiO2复合加入Al2O3抑制γ→θ和θ→α相转变. 掺0.1 mol%Er3+:Al2O3体系粉末,900℃烧结,在1.47—1.63μm波段内光致发光(PL)谱为中心波长1.53 μm、半高宽56 nm的单一宽峰,1000—1200℃烧结,劈裂为多峰PL谱. 掺0.1 mol%Er3+:SiO2-Al2O3复合体系粉末,在高达1200℃烧结,仍保持中心波长1.53 μm的单一宽峰PL谱,由于—OH更完全的脱除,PL强度较900℃烧结Al2O3体系,SiO2-Al2O3复合体系均提高1个数量级. 关键词: 2-Al2O3复合体系')" href="#">SiO2-Al2O3复合体系 掺铒 溶胶-凝胶工艺 光致发光  相似文献   

4.
A visible light-driven photocatalyst, C-doped Zn3(OH)2V2O7, prepared by a hydrothermal method was studied. The as-prepared catalyst was characterized by SEM, XRD, DRS, and XPS, and exhibited efficient photocatalytic activity in the degradation of methylene blue (MB) under visible-light irradiation. Besides decoloring, the decomposition of MB was also observed, further demonstrating the performance of the photocatalyst. The carbon existing on the surface of Zn3(OH)2V2O7 nanorods was free and in carbide form. Dye degradation followed first-order kinetics, and was explained on the basis of the Langmuir-Hinshelwood mechanism.  相似文献   

5.
Titanium dioxide is a well-known photoactive semiconductor with a variety of possible applications. The procedure of pollutant degradation is mainly performed using TiO2 powder suspension. It can also be exploited an immobilized catalyst on a solid support. Morphology and chemical doping have a great influence on TiO2 activity under illumination. Here we compare photoactivity of titania nanotube arrays doped with non-metal atoms: nitrogen, iodine and boron applied for photodegradation of organic dye - methylene blue and terephtalic acid. The doped samples act as a much better photocatalyst in the degradation process of methylene blue and lead to the formation of much higher amount of hydroxyl radicals (•OH) than undoped TiO2 nanotube arrays. The use of a catalyst active under solar light illumination in the form of thin films on a stable substrate can be scaled up for an industrial application.  相似文献   

6.
Experimental data on the heat capacity of the Bi2SiO5 oxide compound and eutectic compositions 75 mol % Bi2O3 + 25 mol % SiO2 and 65 mol % Bi2O3 + 35 mol % GeO2 have been obtained for a wide temperature range.  相似文献   

7.
SrBi2-xHoxNb2O9 (0?≤?x?≤?0.5) ceramics were prepared through the conventional solid state route. The materials have been characterized by XRD, FTIR and SEM. All compounds were pure and well crystallized. In FTIR spectroscopy, the spectral patterns of the crystal structures of these polyphases are unique and smoothly different from each other. The grains were prone to become spherical with increasing x. Dielectric and electrical properties of these materials as a function of temperature at different frequencies have been carried out. The dielectric constant and dielectric loss were found to decrease with an increase of the holmium concentration at room temperature. Reaching up to x?=?0.4 and x?=?0.5, the diffusivity increases, leading to the occurrence of relaxor behavior. 20–30 at.% Ho doping on the Bi-site can fill up the oxygen vacancies and decrease the AC conductivity. However, at higher doping levels greater than 40% holmium oxide, the AC conductivity is found to increase.  相似文献   

8.
The heat capacities of Sm2CuO4 and Ho2Cu2O5 have been measured in the temperature ranges 329–839 and 359–751 K, respectively. The experimental data have been used to determine the thermodynamic properties of the oxide compounds.  相似文献   

9.
在Li2O≥30mol%的Li2O-B2O3-SiO2系统玻璃中,以Li2O代B2O3或SiO2都导致玻璃网络中带非桥氧的硼酸盐和硅酸盐基团的量的增加;以B2O3代SiO2则使玻璃网络中带和不带非桥氧的硼酸盐基团以及带非桥氧的硅酸盐基团的量都增加。 关键词:  相似文献   

10.
The capacitance and voltage (C-V) characteristics of metal, oxide, and semiconductors (MOS) capacitors passivated by SrF2-B2O3-GeO2-SiO2 glasses with various water and fluoride contents were investigated. As the OH absorption coefficient of a glass increased, adverse effects on the recovery of shifts of the hysteresisC-V curve have been observed. The water content of ions is closely related to the fluoride content in the SrF2-B2O3-GeO2-SiO2 glass. The viscous-flow transition point of glass was lowered with increasing degree of ionic character obtained from Hannay's equation.  相似文献   

11.
NiFe2O4/SiO2 nanocomposites were prepared using a sol–gel method with the addition of 3-aminopropyltrimethoxysilane (APS). Different phases and morphologies of NiFe2O4/SiO2 nanocomposites were obtained when different amounts of APS were used. The structural properties of the products were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Sheet-like morphology was observed at higher molar ratio of APS to NiFe2O4, while spherical NiFe2O4/SiO2 nanoparticles separated from each other were formed at lower molar ratio of APS to NiFe2O4. The magnetic properties of the nanocomposites were also investigated, indicating that the interparticle interactions exhibit strong dependence on the molar ratio of APS to NiFe2O4.  相似文献   

12.
A large variety of glass and glass ceramics may be obtained by sol-gel process from hydrolysis of tetraethoxysilane. The transformation involves hydrolysis and polycondensation reactions leading to the growth of clusters that eventually collide together to form a gel. The structure and properties of the final product have been found to be strongly dependent on the initial conditions of preparation. Silica nanocomposites based on Fe2O3/SiO2 were prepared with the help of ultrasonic activation and subsequent annealing in nitrogen atmosphere or air with concentrations of iron oxide of about 20 to 30wt.%.  相似文献   

13.
Cathodoluminescence (CL) properties of SiO2 powders activated with thulium (Tm3+) and holmium (Ho3+) ions prepared by a sol–gel process were investigated. Different molar concentrations of Tm3+ co-doped with Ho3+ were studied. The 460 nm peak was monitored and the influence of the beam energy and concentration of Tm3+ ions on the emission properties of this peak was also monitored. The peculiar behavior whereby the 460 nm emission peak decreases and the increase in the 705 and 865 nm peaks with the increase in the concentration of Tm3+ ions is reported. The relationship between the accelerating beam voltage and the CL intensity of the blue emission peak (460 nm peak) is established. Morphology, particle size and optical properties were characterized with Scanning electron microscopy (SEM), UV/VIS Lambda 750 S spectrometer and Auger electron spectroscopy (AES) equipped with Ocean Optics S2000, respectively.  相似文献   

14.
Three series of catalysts, Ni/Al2O3-SiO2, Ni/Al2O3-Cr2O3 and Ni/SiO2-Cr2O3, were prepared by co-precipitation. In all samples the nickel content was kept constant at 70 at.% Ni, while the support composition was varied. The nickel surface areas, which are required to measure the specific catalytic activities, were determined by hydrogen chemisorption. In the case of the single oxide supported nickel catalysts, the order of the specific catalytic activity values was: Ni/Cr2O3<Ni/Al2O3<Ni/SiO2. The specific catalytic activity of the Ni/Al2O3-SiO2 samples, as a function of the support composition, follows approximately the weighted sum of the specific activities of the single oxide supported nickel catalysts. The specific catalytic activity value of the Ni/Al2O3-Cr2O3 and Ni/SiO2-Cr2O3 samples more closely resembled that of Ni/Cr2O3 catalyst. The presence on chromia surface of the chromic anhydride and its tendency to spread onto are supposed to be the cause of this behaviour. Due to their enhanced activity, the Ni/Al2O3-Cr2O3 catalysts can be used for the production and detritiation of heavy water.  相似文献   

15.
Preparation of Er3+, Ho3+ and Tm3+ ions co-doped SiO2 nanoparticle phosphor powders by sol gel method is reported. The morphology and the particle size of the SiO2 host matrix were confirmed by field emission scanning electron microscopy (FESEM). Ultraviolet, visible (UV/VIS) and cathodoluminescence measurements were carried out in order to investigate the optical properties of our powder phosphors. Green emissions at 520 nm from Er3+ and 544 nm from Ho3+, and red emissions at 665 nm from both Er3+ and Ho3+ ions are reported. Another emission peak in the near infra-red (NIR) region at 875 nm from Er3+ was also measured. Blue emission at 460 nm, red at 705 nm and a NIR peak in the region of 865 nm from Tm3+ were observed. Red, green and blue (RGB) colours were measured from both SiO2:Er3+,Tm3+ and SiO2:Ho3+,Tm3+ systems. The change in the intensities of the emission peaks in both the SiO2:Ho3+,Tm3+ and SiO2:Er3+,Tm3+ systems with the change in accelerating beam voltage is shown. Energy transfer from Tm3+ ions to Er3+ and Ho3+ ions was observed. A mechanism explaining the increase and decrease behaviour of the emission with accelerating beam voltage from both systems is reported.  相似文献   

16.
Muslimov  A. E.  Butashin  A. V.  Grigor’ev  Yu. V.  Kanevsky  V. M. 《JETP Letters》2019,109(9):610-614

The morphology and phase composition of the surface of La3Ga5SiO14 (langasite) crystals at annealing in a temperature range 1000–1200°C have been studied using electron and atomic force microscopy. It has been shown that trigonal lanthanum oxide (La2O3) crystals with sizes to 3–4 μm, as well as a microstructure with sizes to 50 μm with gallium excess, with the approximate composition of 15 mol % La2O3, 65 mol % Ga2O3, and 20 mol % SiO2 are formed on the surface of langasite crystals annealed in air at temperatures above 1100°C. Possible reasons for thermal destruction of the compound can be a significant rearrangement of the disordered crystal structure of langasite caused by the interaction with air oxygen and under the intense surface diffusion of atoms of the crystal, as well as the incongruent character of melting of the La3Ga5SiO14 compound. The revealed thermal destruction of the surface of langasite crystals should be taken into account when using this material to fabricate piezoelectric elements for operation at high temperatures.

  相似文献   

17.
TiO2/SiOx double-layers have been prepared at room temperature by RF magnetron sputtering. The TiO2 top-layer was deposited in an Ar atmosphere, while the SiOx bottom-layer was deposited in an Ar/O2 atmosphere. Samples were characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and photoluminescence techniques. The photocatalytic activity of the samples was evaluated by the photodegradation of methylene blue; the results showed that the photocatalytic activity of the TiO2/SiOx double-layers was superior to that of the TiO2 single-layers. The presence of the SiOx bottom-layer improved the photocatalytic activity of the TiO2 layer because it may act as a trap for electrons generated in the TiO2 layer thus preventing electron-hole recombinations.  相似文献   

18.
Magnetic γ-Fe2O3/SiO2 nanocomposites are synthesized by impregnating mesoporous silica with a hexane solution of γ-iron oxide nanoparticles. Materials with various structural and magnetic properties can be obtained using a subsequent thermal treatment of the synthesized samples (annealing for three hours in an air flow).  相似文献   

19.
NiCuZn ferrites with different contents of CaO-B2O3-SiO2 glasses were synthesized by a conventional ceramic technology and sintered at 1050 °C. It was found that the addition of CaO-B2O3-SiO2 influenced the magnetic and dielectric properties of the ferrites. The saturation magnetization increased at first and reached its maximum with the sample of 2 wt% CaO-B2O3-SiO2, and then decreased. The initial permeability decreased with the content of CaO-B2O3-SiO2 but the cut-off frequency increased. The quality factor decreased first and then increased; the maximum quality factor was obtained in the sample with 3 wt% CaO-B2O3-SiO2. With increasing content of CaO-B2O3-SiO2, the permittivity increased sharply. The possible reasons responsible for these changes are explained.  相似文献   

20.
《Current Applied Physics》2018,18(4):469-476
In order to obtain SrFe12O19 nanoparticles, thermal treatment method was employed, and afterwards SiO2 and TiO2 nanoparticles were embedded in SrFe12O19 matrix SrFe12O19 nanoparticles. The SiO2 and TiO2 nanoparticles' effects were set in SrFe12O19 matrix and experimental techniques which include, transmission electron microscopy (TEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), x-ray analysis (EDX) and field emission scanning electron microscope (FESEM) were used in studying the physical properties of the prepared nanoparticles. The precise DASF method (derivation of absorption spectrum fitting) was employed in examining the optical properties. The addition of SiO2 and TiO2 nanoparticles to SrFe12O19 matrix resulted in the reduction of energy band gap values in compare with the SrFe12O19 nanoparticles. The chemical analysis of SrFe12O19/SiO2, SrFe12O19 nanoparticles, and SrFe12O19/TiO2 nanocomposites was carried out using energy dispersion X-ray analysis (EDX). Ferromagnetic behaviors were demonstrated by SrFe12O19 nanoparticles, SrFe12O19/SiO2 and SrFe12O19/TiO2 nanocomposites, and the behaviors were validated through the use of a vibrating sample magnetometer (VSM). A wasp-waist was observed through hysteresis loop of SrFe12O19/SiO2 nanocomposites, implying the presence of the two magnetic phases; soft and hard ferromagnetic.  相似文献   

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