Luminescence response and CL degradation of combustion synthesized spherical SiO2:Ce nanophosphor

This study was aimed to systematically investigate the luminescence response of SiO₂:Ce³⁺ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO₂:Ce_1m% samples were also annealed at 1000 °C for 1 h in a charcoal environment to reduce incidental Ce⁴⁺ to partial Ce³⁺ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3-8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO₂ was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO₂:Ce³⁺ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO₂:Ce³⁺ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO₂:Ce³⁺ annealed at 1000 °C were obtained.     

Facile fabrication of SiO2/Al2O3 composite microspheres with a simple electrostatic attraction strategy

SiO₂/Al₂O₃ composite microspheres with SiO₂ core/Al₂O₃ shell structure and high surface area were prepared by depositing Al₂O₃ colloid particles on the surface of monodispersed microporous silica microspheres using a simple electrostatic attraction and heterogeneous nucleation strategy, and then calcined at 600 °C for 4 h. The prepared products were characterized with differential thermal analysis and thermogravimetric analysis (DTA/TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). It was found that uniform alumina coating could be deposited on the surface of silica microspheres by adjusting the pH values of the reaction solution to an optimal pH value of about 6.0. The specific surface area and pore volume of the SiO₂/Al₂O₃ composite microspheres calcined at 600 °C were 653 m² g⁻¹ and 0.34 ml g⁻¹, respectively.     

Gd2O3:Eu@mesoporous SiO2 bifunctional core-shell composites: Fluorescence label and drug release

A novel kind of core-shell nanocomposite Gd₂O₃:Eu³⁺@mesoporous SiO₂ was successfully fabricated, which consisted of a solvothermal synthesized Gd₂O₃:Eu³⁺ nanospheres core, a thin nonporous silica midterm layer and an ordered mesoporous silica shell. The XRD, SEM, TEM, FTIR, N₂ adsorption/desorption and PL spectra were employed to characterize the composites. The cytotoxicity of Gd₂O₃:Eu³⁺@mesoporous SiO₂ and Gd₂O₃:Eu³⁺ was assessed by the standard MTT assay. The composites had spherically monodisperse morphology and a narrow size distribution around 180 nm in diameter. Furthermore, they also demonstrated the strong photoluminescence of ⁵D₀-⁷F_J emissions. In addition, the composites exhibited good property of sustained drug release by using ibuprofen (IBU) as model drug in the drug delivery process. Therefore, the drug release process could be easily tracked and identified through photoluminescence. Overall, the present composites have potential significant biomedical application as ideal bifunctional materials.     

Fast and efficient synthesis of ZSM-5 in a broad range of SiO2/Al2O3 without using seeding gel

ZSM-5 zeolite were synthesized in a wide range of SiO₂/Al₂O₃ molar ratios at temperature ranging from 220 to 230 °C without adding seeding gel in 4-6 h of autoclavation time.     

Properties of TiO2 prepared by acid treatment of BaTiO3

TiO₃ powders were prepared by acid treatment of BaTiO₃ and their properties were investigated. The BaTiO₃ powder was subjected to HNO₃ in concentrations ranging from 10⁻³ to 8 M at 90 °C for 0.5-6 h. Dissolution of BaTiO₃ and precipitation of TiO₂ occurred at acid concentrations of 2-5 M. BaTiO₃ dissolves completely to form a clear solution at reaction times of 0.5-1 h, but a rutile precipitate is formed after 2 h of acid treatment. By contrast, anatase is precipitated by adjusting the pH of the clear solution to 2-3 using NaOH or NH₄OH solution. The rutile crystals were small and rod-shaped, consisting of many small coherent domains connected by grain boundaries with small inclination angles and edge dislocations, giving them a high specific surface area (S_BET). With increasing HNO₃ concentration, the S_BET value increased from 100 to 170 m²/g while the crystallite size decreased from 25 to 11 nm. The anatase crystals obtained here were very small equi-axial particles with a smaller crystallite size than the rutile and S_BET values of about 270 m²/g (higher than the rutile samples). The photocatalytic activity of these TiO₂ was determined from the decomposition rate of Methylene Blue under ultraviolet irradiation. Higher decomposition rates were obtained with larger crystallite sizes resulting from heat treatment. The maximum decomposition rates were obtained in samples heated at 500-600 °C. The photocatalytic activity of the TiO₂ was found to depend more strongly on the sample crystallite size than on S_BET.     

A low-temperature process to synthesize rutile phase TiO2 and mixed phase TiO2 composites

This works employed K₂Ti₄O₉, a novel Ti source, to prepare TiO₂ powders. By a “low-temperature dissolution-reprecipitation process” (LTDRP), rutile phase TiO₂ was successfully synthesized after reacting at 50 °C for 48 h. The obtained sample showed a specific surface area about 45 m²/g, and excellent activity in photo-destruction of NO_x gas. The coupling of rutile phase TiO₂ with commercial anatase TiO₂ showed significant effect in further enhancing the photocatalytic activity.     

Preparation and characterization of the TiO2 ultrafine particles by detonation method

Utilizing the raw materials of TiOSO₄, NaOH, NH₄NO₃ and RDX, the TiO₂ ultrafine particles were prepared under high pressure and high temperature by detonation method. The structure, composition and size distribution of the TiO₂ ultrafine particles were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated the as-prepared TiO₂ ultrafine particles exhibited spherical-like grains and that the average size of particles was 25 ± 5 nm. After being heated at 700 °C for 1 h, TiO₂ particles have entirely completed the anatase-rutile phase transition, which means that detonation method can effectively enhance the anatase-rutile phase transition by lowering the transition temperature. The size of TiO₂ nanoparticles can be effectively controlled because the as-prepared nanoparticles do not have enough time to grow to large and perfect crystallites during the detonation process.     

M2Y8(SiO4)6O2: Tb (M = Ca, Sr) phosphors: Sol-gel synthesis from N-2-aminoethylic-3-aminopropyldiethoxysilane and different photoluminescence behavior

M₂Y₈(SiO₄)₆O₂: Tb³⁺ (M = Ca, Sr) phosphors have been synthesized with a new silicon source silane crosslinking reagent (N-2-aminoethylic-3-aminopropyldiethoxysilane [NH₂(CH₂)₂NH(CH₂)₃SiCH₃(OCH₃)₂], abbreviated as AEAPMMS) through the sol-gel process, both of which present the characteristic emission ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) of Tb³⁺ ions. It is interesting to be found that the high energy level blue emission (⁵D₃ → ⁷F_J (J = 6, 5, 4, 3) transition) still can be found in the emission spectrum of Ca₂Y₈(SiO₄)₆O₂: Tb³⁺ while it disappears in the emission spectrum of Sr₂Y₈(SiO₄)₆O₂: Tb³⁺ for the cross-relaxation-induced quenching.     

Novel Dy-doped Ca2Gd8(SiO4)6O2 white light phosphors for Hg-free lamps application

The luminescent properties of Ca₂Gd_8(1−x)(SiO₄)₆O₂:xDy³⁺ (1% ≤ x ≤ 5%) powder crystals with oxyapatite structure were investigated under vacuum ultraviolet excitation. In the excitation spectrum, the peaks at 166 nm and 191 nm of the vacuum ultraviolet region can be assigned to the O²⁻ → Gd³⁺, and O²⁻ → Dy³⁺ charge transfer band respectively, which is consistent with the theoretical calculated value using Jφrgensen's empirical formula. While the peaks at 183 nm and 289 nm are attributed to the f-d spin-allowed transitions and the f-d spin-forbidden transitions of Dy³⁺ in the host lattice with Dorenbos's expression. According to the emission spectra, all the samples exhibited excellent white emission under 172 nm excitation and the best calculated chromaticity coordinate was 0.335, 0.338, which indicates that the Ca₂Gd₈(SiO₄)₆O₂:Dy³⁺ phosphor could be considered as a potential candidate for Hg-free lamps application.     

SiO2/TiO2 multilayer films grown on cotton fibers surface at low temperature by a novel two-step process

A novel two-step process was developed to synthesize and deposit SiO₂/TiO₂ multilayer films onto the cotton fibers. In the first step, SiO₂ particles on cotton fiber surface were synthesized via tetraethoxysilane hydrolysis in the presence of cotton fibers, in order to protect the fibers against photo-catalytic decomposition by TiO₂ nanoparticles. In the second step, the growth of TiO₂ nanoparticles into the modified cotton fiber surface was carried out via a sol-gel method at the temperature as low as 100 °C. The as-obtained SiO₂/TiO₂ multilayer films coated on cotton fibers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and X-ray diffraction, respectively.     

Effect of liquid-forming additives on the sintering and mechanical properties of Al2O3/3Y-TZP (30 vol.%) composite

Al₂O₃/3Y-TZP (30 vol.%) composite was pressurelessly sintered with addition of TiO₂MnO₂ and/or CaOAl₂O₃SiO₂ glass. It was found that TiO₂MnO₂ addition greatly enhanced the densification of the composite by the formation of a low-viscosity liquid at sintering temperature. In contrast, the high-viscosity liquid formed by CaOAl₂O₃SiO₂ glass improved mechanical properties because of its repressing effect on grain growth. The composite could be obtained at a temperature as low as 1400°C by co-doping with TiO₂MnO₂ and CAS glass. Bending strength of 552±64 MPa and fracture toughness of 6.03±0.22 MPa m^1/2 were obtained with a doping level of 2 wt.% TiO₂MnO₂ and 2 wt.% CAS glass.     

Physicochemical characterization of Fe3O4/SiO2/Au multilayer nanostructure

The purpose of this research was to synthesize and characterize gold-coated Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetite nanoparticles (NPs) were prepared using co-precipitation method. Smaller particles were synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g⁻¹. For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of 80–100 emu g⁻¹ and coercivity of 80–120 Oe for particles between 35 and 96 nm, respectively. The magnetic NPs were modified with a thin layer of silica using Stober method. Small gold colloids (1–3 nm) were synthesized using Duff method and covered the amino functionalized particle surface. Magnetic and optical properties of gold nanoshells were assessed using Brunauer–Emmett–Teller (BET), vibrating sample magnetometer (VSM), UV–Vis spectrophotometer, atomic and magnetic force microscope (AFM, MFM), and transmission electron microscope (TEM). Based on the X-ray diffraction (XRD) results, three main peaks of Au (1 1 1), (2 0 0) and (2 2 0) were identified. The formation of each layer of a nanoshell is also demonstrated by Fourier transform infrared (FTIR) results. The Fe₃O₄/SiO₂/Au nanostructures, with 85 nm as particle size, exhibited an absorption peak at ∼550 nm with a magnetization value of 1.3 emu g⁻¹ with a specific surface area of 71 m² g⁻¹.     

Decomposition of the molecular precursor Bu4Sn6S6 on the surface of TiO2 to prepare semiconductor composite photocatalysts

In this work, the single source organometallic precursor Bu₄Sn₆S₆ was impregnated and decomposed on the surface of TiO₂ to produce semiconductor composites. ¹¹⁹Sn Mössbauer, Raman and ultra violet/visible spectroscopies, powder X-ray diffraction, temperature programmed reduction and surface area suggest for Sn contents of 1, 5 and 10 wt%, the formation of a highly dispersed unstable SnS phase which is readily oxidized by air at room temperature to form SnO₂ on the TiO₂ surface. The composite with Sn 30 wt% produced a mixture with the phases SnS/γ-Sn₂S₃ and SnO₂. Photocatalytic experiments with the composites SnX_n/TiO₂ using the textile dye Drimaren red as a probe molecule showed a first-order reaction with rate constants k_absorbance for the composites with Sn 1 and 5% higher than pure TiO₂ which was explained by the formation of the more active photocatalyst composite SnO₂/TiO₂.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

Size variation and optical absorption of sol-gel Ag nanoparticles doped SiO2 thin film

In this research, we have focused on the formation of Ag nanoparticles dispersed in SiO₂ matrix using sol-gel method. The influences of the metal concentration on the size variation of Ag nanoparticles and the size effect on the surface plasmon absorption have been studied. Sol-gel silica thin films containing Ag particles were synthesized by dip-coating on soda-lime glasses. The molar ratio of Ag / Si was chosen from 0.2% to 8%. All films were dried in air at 100 °C for 1 h. Using X-ray photoelectron spectroscopy, the Ag / Si ratios in the prepared films have been measured. In addition, it was shown that the prepared matrix was a stoichiometric composition as SiO₂, and the synthesized nanoparticles were mainly in the metallic state. Size and distribution of the nanoparticles were measured by high resolution scanning as well as transmission electron microscopy and also atomic force microscopy analyses for low and high Ag concentrations, respectively. We have found that by decreasing the Ag / Si ratio from 8 to 0.2 mol%, the particle size reduces from 95 to 4 nm with a nearly spherical shape. UV-visible spectrophotometry showed that the size reduction of the Ag nanoparticles for the Ag / Si molar ratios ranging from 8 to 0.2 mol% leads to an intensity reduction of the absorption peak and a blue shift from 460 to 410 nm.     

Studies of bacterial adhesion on TiN, SiO2-TiO2 and hydroxyapatite thin layers deposited on titanium and Ti6Al4V alloy for medical applications

The Staphylococcus epidermidis biofilm formation on titanium or titanium alloy, coated with TiN, SiO₂-TiO₂ and electrodeposited hydroxyapatite, was tested. Surfaces of titanium, Ti6Al4V alloy or TiN, modified with SiO₂-TiO₂ layer, were found to be highly resistant to bacterial adhesion. Only small amounts of bacterial cells were observed on matrices coated by thin hydroxyapatite films, deposited on both SiO₂-TiO₂ and TiN + SiO₂-TiO₂ interlayers. Biological tests showed that the biofilm formed massively on polished and ground titanium and titanium alloy surfaces, also those covered with TiN, but not on those modified with SiO₂-TiO₂ nanofilm.     

High-performance ZnO thin film transistors with sputtering SiO2/Ta2O5/SiO2 multilayer gate dielectric

A high-performance ZnO thin film transistor （ZnO-TFT） with SiO₂/Ta₂O₅/SiO₂ (STS) multilayer gate insulator is fabricated by sputtering at room temperature. Compared to ZnO-TFTs with sputtering SiO₂ gate insulator, its electrical characteristics are significantly improved, such as the field effect mobility enhanced from 11.2 to 52.4 cm²/V s, threshold voltage decreased from 4.2 to 2 V, and sub-threshold swing improved from 0.61 to 0.28 V/dec. The improvements are attributed to the high gate capacitance (from 50 to 150 nF/cm²) as well as nice surface morphology by using dielectric with high～k Ta₂O₅ sandwiched by SiO₂ layers. The capacitance-voltage characteristic of a metal-insulator-semiconductor capacitor with the structure of Indium Tin Oxide/STS/ZnO/Al was investigated and the trap charges at the interface or bulk is evaluated to be 2.24 × 10¹² cm⁻². From the slope of C⁻² versus gate voltage, the doping density N_D of ZnO is estimated to be 1.49 × 10¹⁶ cm⁻³.     

Grazing incidence X-ray study of Ge-nanoparticle formation in (Ge:SiO2)/SiO2 multilayers

We present the study of formation of Ge-nanoparticles (Ge-NP) in germanosilicate (Ge:SiO₂) multilayer (ML) films under thermal treatment. In anticipation of controllable formation of Ge-NP, ML films were prepared by magnetron deposition at room temperature as 20 bi-layer stacks, each bi-layer comprised of a 7 nm thick layer of (Ge + SiO₂) (molar ratio: 60:40) succeeded by a 7 nm thick layer of pure SiO₂, and then annealed for 1 h, up to T_a = 900 °C. Formation and morphology of Ge-NP were analyzed by combining the information obtained from the grazing incidence small angle X-ray scattering and X-ray diffraction. It was found that precipitation of Ge-NP starts at T_a = 600 °C, while high degree of in-plane confinement and lateral ordering of rather uniform precipitated particles is achieved at T_a =  700-800 °C range. At still higher annealing temperature T_a > 800 °C, volume fraction of precipitated Ge-NP in SiO₂ matrix diminishes due to the out-diffusion of Ge atoms from the film, while Ge-NP are no more well confined to (Ge + SiO₂) layers.     

Preparation and super-hydrophilic properties of TiO2/SnO2 composite thin films

SnO₂-TiO₂ composite thin films were fabricated on soda-lime glass with sol-gel technology. By measuring the contact angle of the film surface and the degradation of methyl orange, we studied the influence of SnO₂ doping concentration, heat-treatment temperature and film thickness on the super-hydrophilicity and photocatalytic activity of the composite films. The results indicate that the doping of SnO₂ into TiO₂ can improve their hydrophilicity and photocatalytic activity, and the composite film with 1-5 mol% SnO₂ and heat-treated at 450°C is of super-hydrophilicity. The optimal SnO₂ concentration for the photocatalytic activity is 10 mol% and larger film thickness is helpful to reduce the contact angle of the composite films.     

Large-scale synthesis of ear-like Si3N4 dendrites from SiO2/Fe composites and Si powders

Large-scale ear-like Si₃N₄ dendrites were prepared by the reaction of SiO₂/Fe composites and Si powders in N₂ atmosphere. The product was characterized by field emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results reveal that the product mainly consists of ear-like Si₃N₄ dendrites with crystal structures, which have a length of several microns and a diameter of 100-200 nm. Nanosized ladder-like Si₃N₄ was also obtained when changing the Fe content in the SiO₂/Fe composites. The Si₃N₄ nanoladders have a length of hundreds nanometers to several microns and a width of 100-300 nm. The ear-like Si₃N₄ dendrites are formed from a two-step growth process, the formation of inner stem structures followed by the epitaxial growth of secondary branches.