Silica Nanocrystals Research Articles

Surface coated red phosphors with silica nanoparticles and silica nanocomposites: performance modifications

Surface coverings using nanomaterials of silica nanoparticles and poly (methyl methacrylate) – abbreviated “PMMA-silica nanomaterials” – are introduced to the Y 2 O 2 S:Eu 3+ phosphor through four distinct approaches. The objective is to enhance Y 2 O 2 S:Eu 3+ phosphorescence and prolonged sustainability. Using immerse-daubing along with sol-gel approach (Stober way), it is possible to have Y 2 O 2 S:Eu 3+ phosphors covered with relatively-monodisperse nano-silica particles (5 nm). To create the silica nano-crystals employed in the coating process of phosphors, we carry out concurrently hydrolysis and condensation procedures to develop the formation and basic polymerization utilizing poly (1-vinyl-2-pyrrolidone). The surface coating layer for Y 2 O 2 S:Eu 3+ spheres, which comprises polymethyl methacrylate (PMMA)-silica nanocomposites, can be formed in two ways: by combining silica nanogranules with methyl methacrylate (MMA) monomer as well as through subjecting MMA to tetraethyl orthosilicate (Si(OC₂H₅)₄) chemical compound. The latter approach demonstrated is considered the highest augmentation in phosphorescence and prolonged sustainability for Y 2 O 2 S:Eu 3+ spheres. Specifically, when using the second approach to get PMMA-silica phosphor coating, Y 2 O 2 S:Eu 3+ exhibited a 5-percent increase in the phosphorescent intensity, compared to untreated phosphors. Contrary to a drop in cathode phosphorescence (CP) output and a rising bombardment duration for exposed phosphor, the latter technique produces a practically constant CP energy with PMMA-silica nanocomposite covered phosphors.

Enhanced catalytic activity of platinum decorated silica nanocrystals in rapid reduction of organic dyes

Pt decorated silica (Pt/SiO2) nanocrystals (NCs) were synthesized using a chemical route, and their activities were evaluated towards the reduction of Methylene Blue (MB), Rhodamine B (RhB) and p-Nitrophenol (PNP). X-ray diffraction (XRD) analysis confirmed cubic crystal structure of Pt NCs. The formation of monodispersed spherical SiO2 nanoparticles with an average particle size of ∼150 nm was confirmed by Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy. The High Resolution TEM confirmed cubic crystal structure of Pt NCs having lattice fringes with interplaner spacing of ∼0.29 nm, corresponding to (111) plane. The catalytic activities of the Pt/SiO2 NCs towards MB, RhB and PNP were studied using UV-visible spectrophotometer. The Pt/SiO2 NCs showed excellent catalytic activity with pseudo first order rate constant values 0.016 s−1, 0.011 s−1, 0.006 s−1 for MB, RhB and PNP, respectively. The synthetic method used in the present work offers valuable insights for facile preparation of Pt/SiO2 NCs as an efficient and valuable catalyst for environmental remediation.

Spectroscopic and Quantum Chemical Computational Studies of Silica Nanocrystals Extracted from Rice Straw

Spectroscopic and Quantum Chemical Computational Studies of Silica Nanocrystals Extracted from Rice Straw

Confinement creates a 9 GPa ambience: emergence of cristobalite phases in a silica film

We present here the results of the x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Analysis of x-rays (EDAX), x-ray Reflectivity (XRR), Secondary Ion Mass spectroscopy (SIMS) and x-ray Diffraction (XRD) studies of silica films spin-coated from a Tetraethyl Orthosilicate (TEOS) precursor on native and hydrophilized Al substrates. It is observed that the substrates are mainly porous (porosity ∼ 33%) AlO(OH), there is a diffuse interlayer of highly porous (porosity ∼ 90%) AlO(OH), essentially a modification of the substrate, and a top layer of silica composed of nanocrystals with in-plane dimensions of 100–300 nm and thickness of 2.5 nm with a sharply defined silica-hydrated alumina interface. The silica nanocrystals were found in the metastable high pressure cristobalite phases with the tetragonal or α-phase co-existing in its low (0.77 GPa) and high (9 GPa) pressure structures. This indicates a high normal stress developed from the confinement and provides a basis for the quantitative assessment of the confinement force, which comes out to be higher in value than the van der Waals force but weaker than the Hydrogen bonding force.

Luminescence of ZnO nanocrystals in silica synthesized by dual (Zn, O) implantation and thermal annealing

Zinc blende ZnO nanocrystals (NCs) were synthesised in amorphous silica by high-fluence dual (Zn, O) ion implantation and subsequent thermal annealing in air. We observed the formation of core/shell nanoparticles at the depth of maximum Zn concentration as a result of an incomplete oxidation process. The silica matrix with ZnO NCs exhibits an intense white-greenish emission. Low-temperature photoluminescence spectroscopy revealed various radiative recombination mechanisms in the zinc blende ZnO NCs involving intrinsic defects that act as donors and acceptors.

Silica-Based Organic-Inorganic Hybrid Fluorescent Ink for Security Applications.

A facile formulation of fast-drying fluorescent ink made from nanostructured fluorescent silica nanocrystals is presented. The rheostable viscous ink suitable for screen printing was developed by careful selection of organic vehicle components, which was later printed onto various rigid and flexible substrates. Photoluminescence studies of the printed film confirmed that the formulated ink composition did not show noticeable influence on the excitation property of the fluorescent silica. The developed cost-effective and fast-curing fluorescent silica ink with desirable luminescent property makes it a suitable candidate for information encryption, optical devices, and energy conversion applications.

Site-specific sonocatalytic tumor suppression by chemically engineered single-crystalline mesoporous titanium dioxide sonosensitizers

The biomedical applications of TiO2-based nanosystems develop very slowly among diverse inorganic bio-nanosystems (e.g., Fe3O4, SiO2, MnO, Au, etc.) due to the lack of adequate synthetic strategies to fabricate TiO2 nanoparticles with desirable nanostructures and their specific light responses in the ultraviolet range with potential phototoxicity and low tissue-penetrating capability. In this work, we report on the rational design and fabrication of colloidal single-crystalline and mesoporous anatase TiO2 nanoparticles (MTNs) with high dispersity, well-defined mesoporosity, uniform morphology and nanosized single-crystalline structure, employing a facile yet versatile bottom-up chemical strategy, i.e., pre-hydrolysis of titanium precursors combined with subsequent solvothermal treatment (PH-ST) simply using water as the additive. Highly biocompatible PEGylated MTNs have exerted their unique function as efficient sonosensitizers for sonodynamic therapy (SDT) of cancer, as systematically demonstrated both in vitro and in vivo. The production of reactive oxygen species (ROS) by MTN-sonosensitized SDT has been demonstrated to be the mechanism for efficient tumor SDT. The in vivo biocompatibility assay revealed that either a single dose at 150 mg kg-1 or repeated doses at as high as a total of 400 mg kg-1 exhibited no obvious in vivo toxicity. The ultrasound irradiation of MTNs in SDT is expected to break the depth shadow of light responsiveness of TiO2-based nanosystems in the ultraviolet range, and the presence of well-defined mesoporous nanostructures of MTNs shows great potential for the delivery of therapeutic agents for combined cancer therapy.

Influence of Nanosized Silicon Oxide on the Luminescent Properties of ZnO Nanoparticles

For practical use of nanosized zinc oxide as the phosphor its luminescence quantum yields should be maximized. The aim of this work was to enhance luminescent properties of ZnO nanoparticles and obtain high-luminescent ZnO/SiO2composites using simpler approaches to colloidal synthesis. The luminescence intensity of zinc oxide nanoparticles was increased about 3 times by addition of silica nanocrystals to the source solutions during the synthesis of ZnO nanoparticles. Then the quantum yield of luminescence of the obtained ZnO/SiO2composites is more than 30%. Such an impact of silica is suggested to be caused by the distribution of ZnO nanocrystals on the surface of silica, which reduces the probability of separation of photogenerated charges between the zinc oxide nanoparticles of different sizes, and as a consequence, there is a significant increase of the luminescence intensity of ZnO nanoparticles. This way of increasing nano-ZnO luminescence intensity facilitates its use in a variety of devices, including optical ultraviolet and visible screens, luminescent markers, antibacterial coatings, luminescent solar concentrators, luminescent inks for security printing, and food packaging with abilities of informing consumers about the quality and safety of the packaged product.

Bioinspired enzymatic synthesis of silica nanocrystals provided by recombinant silicatein from the marine sponge Latrunculia oparinae.

The process of silica formation in marine sponges is thought to be mediated by a family of catalytically active structure-directing enzymes called silicateins. It has been demonstrated in biomimicking syntheses that silicateins facilitated the formation of amorphous SiO2. Here, we present evidence that the silicatein LoSiLA1 from the marine sponge Latrunculia oparinae catalyzes the in vitro synthesis of hexa-tetrahedral SiO2 crystals of 200–300 nm. This was possible in the presence of the silica precursor tetrakis-(2-hydroxyethyl)-orthosilicate that is completely soluble in water and biocompatible, experiences hydrolysis–condensation at neutral pH and ambient conditions.

Silica nanocrystal/graphene composite with improved photoelectric and photocatalytic performance

A modified Stöber process using vinyltriethoxysilane as the precursor and in the presence of graphene oxide unprecedentedly leads to the exclusive growth of monodispersed silica nanocrystals (SiO2 NCs) (ca. 3–4nm) at room-temperature on single-layer graphene sheet with a high deposition density (ca. 1016/m2), where graphene oxide is simultaneously reduced by ammonia. Well-resolved lattice fringes with the spacing of 0.19nm demonstrate the excellent crystallinity of SiO2 NC, which has an absorption band in the range of 200–400nm. The anchoring of vinyl-silanols on graphene oxide through SiOC oxo-bridging and the π–π interaction between double bonds of vinyl-silanols and graphene oxide co-direct the orderly growth of SiO2 NC nuclei on graphene. Compared with isolate and physically mixed SiO2 and graphene, the composite has decreased impedance and 4.5 times improved photocurrent, which also shows extraordinarily high photocatalytic activity toward the degradation of organic pollutant.

Photoluminescence enhancement of silicon nanocrystals placed in the near field of a silicon nanowire

Semiconductor nanowires have an excellent ability to trap, guide, scatter, or absorb light for specific morphology-dependent resonant optical modes. The electromagnetic field enhancement associated with these modes could be used to modify the luminescence of emitters positioned in the vicinity of the nanowire, in a way similar to plasmonic nanostructures. We show that the photoluminescence of a single plane of silicon nanocrystals in silica, positioned at about 3 nm below the surface, can be enhanced by a factor of 2 to 3 in the presence of a silicon nanowire antenna on the silica surface. This could be the basis of a promising fully complementary metal oxide semiconductor compatible process to improve silicon-based light emitting devices, despite a lower enhancement compared to plasmonic nanostructures. Two-dimensional photoluminescence maps recorded for different polarization configurations (incident electric field parallel or perpendicular to the nanowire axis) exhibit different behaviors and can be related to the electric field intensity distribution in the near-field region of the nanowire, where the active silicon nanocrystal layer is located.

Confined growth of highly uniform and single bcc-phased FeCo/graphitic-shell nanocrystals in SBA-15

We have synthesized highly uniform and single bcc-phased FeCo/graphitic carbon shell (FeCo/GC) nanocrystals with an average diameter of 5.7±0.3nm by thermal decomposition of metal precursors in SBA-15 and subsequent methane CVD. Small-angle XRD data and N2 adsorption–desorption isotherms of the SBA-15 before and after loading with FeCo/GC nanocrystals clearly demonstrate that the structure of SBA-15 was retained during the nanocrystal growth and most of the channels of the mesoporous silica were stucked by the FeCo/GC nanocrystals. The nanocrystal sizes of 5–6nm are consistent with the pore diameters of the SBA-15. The yield of nanocrystals in silica has been increased 6-fold and the Fe/Co ratio of the FeCo/GC nanocrystals has been improved from 34:66 to 46:54 by using SBA-15 instead of fumed silica. The FeCo/GC nanocrystals exhibit superparamagnetism with high saturation magnetization of 209emu/g metal at room temperature.

(Invited) Optical and Structural Properties of Silicon Nanocrystals and Laser-Induced Thermal Effects

Si nanocrystals in silica are attractive for photonic applications. Various optical functions can be realized in this way (for example, light emission). The optical and structural properties of a variety of such materials are described and compared here. It is found that Si nanocrystals with diameters 3-4 nm are not a direct source of the 1.5-eV photoluminescence. Furnace annealing at temperatures up to 1200 °C does not complete the Si SiO2 phase separation, and the suboxide phase and very small Si clusters should be accounted for when discussing light-emission mechanisms. Laser-induced thermal effects on optical and structural properties of free-standing films are described in detail. Laser annealing produces macroscopic Si-SiO2 phase separation and compressive stress on Si nanocrystals. The laser-induced structural changes offer an approach to optical memory with a high data density and superior thermal stability.

Optical and Structural Properties of Silicon Nanocrystals and Laser-Induced Thermal Effects

Si nanocrystals in silica are attractive for photonic applications. Various optical functions can be realized in this way (for example, light emission). The optical and structural properties of a variety of such materials are described and compared here. It is found that Si nanocrystals with diameters 3-4 nm are not a direct source of the 1.5-eV photoluminescence. Furnace annealing at temperatures up to 1200°C does not complete the Si-SiO2 phase separation, and the suboxide phase and very small Si clusters should be accounted for when discussing light-emission mechanisms. Laser-induced thermal effects on optical and structural properties of free-standing films are described in detail. Laser annealing produces macroscopic Si-SiO2 phase separation and compressive stress on Si nanocrystals. The laser-induced structural changes offer an approach to optical memory with a high data density and superior thermal stability.

Study of erbium-doped silicon nanocrystals in silica

Er-doped SiO2 and Er-doped Si-NCs embedded in a SiO2 matrix were produced by Er and/or Si ion beam implantation of a Si (100) substrate. The composition and distribution of implanted Er varies in samples either with or without Si implants. HAADF and EELS detail in samples with Si implants, the Si and Er distribution is identical, and within a band of ~110 nm width at ~75 nm below the SiO2 surface. Intense PL emission at 1.54 μm confirms formation of ErSi2, for the majority of aggregates, is unlikely. The present investigation details most Si-NCs are surrounded by Er2O3, or possess this phase within.

Modification of Ag containing photo-thermo-refractive glasses induced by electron-beam irradiation

We present the experimental investigation of formation and growth of Ag nanocrystals in silica photo-thermo-refractive glasses under the electron-beam irradiation and subsequent thermal treatment. The influence of electron irradiation fluence, current density and thermal treatment conditions on nanocrystal growth dynamic has been investigated. Theoretical models and computer simulation of main processes which take place during electron-beam irradiation are presented.

Ultrafast All-Optical Switching in a Silicon-Nanocrystal-Based Silicon Slot Waveguide at Telecom Wavelengths

We demonstrate experimentally all-optical switching on a silicon chip at telecom wavelengths. The switching device comprises a compact ring resonator formed by horizontal silicon slot waveguides filled with highly nonlinear silicon nanocrystals in silica. When pumping at power levels about 100 mW using 10 ps pulses, more than 50% modulation depth is observed at the switch output. The switch performs about 1 order of magnitude faster than previous approaches on silicon and is fully fabricated using complementary metal oxide semiconductor technologies.

In vivo study of genotoxicity and teratogenicity of silica nanocrystals

The potential genotoxicity of silica nanocrystals (nc-Si) (size 2-7 nm with their agglomerates 5 μm) in mice and influence of nc-Si on the embryonal and the postnatal development of the rats were evaluated. No clastogenic effects were observed in bone marrow cells of mice intraperitoneally exposed to single doses of nc-Si 5, 25 and 50 mg/kg for 24 hr or to doses 5 and 25 mg/kg for seven and 14 days. Comet assay revealed a significant increase in tail DNA percentage in the bone marrow cells of mice treated with nc-Si at a single dose 5 mg/kg for 24 h and both in bone marrow and brain cells when nc-Si was used at a dose 50 mg/kg. There was no significant increase in DNA damage after a 3 h treatment with nc-Si at doses 5 and 25 mg/kg. Also, no elevated DNA damage was observed in mice exposed to nc-Si at 5 mg/kg dose for seven days. Dose of nc-Si at 50 mg/kg caused death of 40-60% of the animals within 2-3 days that made impossible evaluation genotoxicity in this dose at long-term exposure. Nc-Si injected intraperitoneally to rats at a dose of 50 mg/kg on the 1st, 7th and 14th days of pregnancy showed no teratogenicity and had no influence on postnatal development of pups. But negative influence on body weight gain in pregnant rats and newborns at some stages of the experiment was noticed.

Photoluminescence and charge storage characteristics of silica nanocrystals: The role of stress-induced interface defects

SiO 2 nanocrystals embedded in Lu 2O 3 thin film were fabricated using pulsed-laser deposition method. Two dimensional finite element calculations clearly reveal that SiO 2 nanocrystals certainly experienced great compressive stress in Lu 2O 3 thin film. This may lead to a great deal of stress-induced defects at the interface of SiO 2 nanocrystals embedded in Lu 2O 3 thin film and thus induced the observed photoluminescence peak and charge storage properties. The findings presented here indicate that the matrix environment of the nanocrystals plays a significant role in determining their electrical and optical properties.

Optical properties of silicon nanocrystals in silica: Results from spectral filtering effect, m-line technique, and x-ray photoelectron spectroscopy

The optical properties of silica layers containing silicon nanocrystals are analyzed in terms of spectral filtering in absorbing planar waveguides (cutoff spectra), m-line measurements, and x-ray photoelectron spectroscopy (XPS). The effects of optical dispersion, approximation of weak guiding, and depth dependence of refractive index in a planar waveguide are studied. We compare the measured optical properties of silicon-rich silicon oxide samples with the values estimated by the Bruggeman theory using the XPS structural components. A good agreement between the measured and calculated refractive indices is found. The results for absorption suggest high transparency of the nanoscale-suboxide component in contrast to the corresponding bulk material. The Raman intensity of silicon nanocrystals is proportional to the XPS amount of bulk silicon. The extinction coefficient extracted for the Si component is between the values for crystalline and amorphous silicon. Annealing at higher temperatures decreases the Si component extinction coefficient, which is interpreted as a decrease in the amorphous Si fraction. The XPS method surprisingly suggests a large proportion of silicon suboxide even after annealing at 1200 °C.