Doped Sol Gel Silica Research Articles

Properties of Gd-Doped Sol-Gel Silica Glass Radioluminescence under Electron Beams

The radiation-induced emission (RIE) of Gd3+-doped sol-gel silica glass has been shown to have suitable properties for use in the dosimetry of beams of ionizing radiation in applications such as radiotherapy. Linear electron accelerators are commonly used as clinical radiotherapy beams, and in this paper, the RIE properties were investigated under electron irradiation. A monochromator setup was used to investigate the light properties in selected narrow wavelength regions, and a spectrometer setup was used to measure the optical emission spectra in various test configurations. The RIE output as a function of depth in acrylic was measured and compared with a reference dosimeter system for various electron energies, since the dose-depth measuring abilities of dosimeters in radiotherapy is of key interest. The intensity of the main radiation-induced luminescence (RIL) of the Gd3+-ions at 314 nm was found to well represent the dose as a function of depth, and was possible to separate from the Cherenkov light that was also induced in the measurement setup. After an initial suppression of the luminescence following the electron bunch, which is ascribed to a transient radiation-induced attenuation from self-trapped excitons (STEX), the 314 nm component was found to have a decay time of approximately 1.3 ms. An additional luminescence was also observed in the region 400 nm to 600 nm originating from the decay of the STEX centers, likely exhibiting an increasing luminescence with a dose history in the tested sample.

Radioluminescence Response of Ce-, Cu-, and Gd-Doped Silica Glasses for Dosimetry of Pulsed Electron Beams.

Radiation-induced emission of doped sol-gel silica glass samples was investigated under a pulsed 20-MeV electron beam. The studied samples were drawn rods doped with cerium, copper, or gadolinium ions, which were connected to multimode pure-silica core fibers to transport the induced luminescence from the irradiation area to a signal readout system. The luminescence pulses in the samples induced by the electron bunches were studied as a function of deposited dose per electron bunch. All the investigated samples were found to have a linear response in terms of luminescence as a function of electron bunch sizes between Gy/bunch and Gy/bunch. The presented results show that these types of doped silica rods can be used for monitoring a pulsed electron beam, as well as to evaluate the dose deposited by the individual electron bunches. The electron accelerator used in the experiment was a medical type used for radiation therapy treatments, and these silica rod samples show high potential for dosimetry in radiotherapy contexts.

Epitaxial Nanostructured α-Quartz Films on Silicon: From the Material to New Devices.

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all the steps in the process starting from the material to the device fabrication. The epitaxial growth of α-quartz film on SOI (100) substrate starts with the preparation of a strontium doped silica sol-gel and continues with the deposition of this gel into the SOI substrate in a thin film form using the dip-coating technique under atmospheric conditions at room temperature. Before crystallization of the gel film, nanostructuration is performed onto the film surface by nanoimprint lithography (NIL). Epitaxial film growth is reached at 1000 °C, inducing a perfect crystallization of the patterned gel film. Fabrication of quartz crystal cantilever devices is a four-step process based on microfabrication techniques. The process starts with shaping the quartz surface, and then metal deposition for electrodes follows it. After removing the silicone, the cantilever is released from SOI substrate eliminating SiO2 between silicon and quartz. The device performance is analyzed by non-contact laser vibrometer (LDV) and atomic force microscopy (AFM). Among the different cantilever's dimensions included in the fabricated chip, the nanostructured cantilever analyzed in this work exhibited a dimension of 40 µm large and 100 µm long and was fabricated with a 600 nm thick patterned quartz layer (nanopillar diameter and separation distance of 400 nm and 1 µm, respectively) epitaxially grown on a 2 µm thick Si device layer. Themeasuredresonance frequency was267 kHz and the estimated quality factor, Q, of the whole mechanical structure was Q ~ 398 under low vacuum conditions. We observed the voltage-dependent linear displacement of cantilever with both techniques (i.e., AFM contact measurement and LDV). Therefore, proving that these devices can be activated through the indirect piezoelectric effect.

Comparative study of oscillator strengths in dye and metal doped silica glasses

In the present study sol gel silica glasses doped with rhodamine dye (Rh6G) and transition metals like silver, copper and iron were prepared at room temperature through sol gel route. The molar concentrations of dye and metal are varied and synthesized to get a uniform dye and metal doped clusters in silica matrices. Structural characterization is performed by SEM and XRD on doped silica glasses. SEM micrographs reveal the size of particles to be 10-50μm. The amorphous structures of the glasses are confirmed by XRD. The absorption spectra are monitored and analyzed. The absorption spectra of fluorescent dye doped sol gel silica glasses are found within the limit of 400-600 nm and the absorption spectra of different metal doped glasses are in the range of 250-350nm. Oscillator strengths of dye doped and metal doped glasses are calculated and compared. Oscillator strength of rhodamine dye doped silica glasses is comparatively higher than the other doped glasses. Silver is seen to have high oscillator strength among the metal doped silica glasses.

Effect of Tm3+ concentration on the emission wavelength shift in Tm3+-doped silica microsphere lasers.

In this work, a Tm3+-doped solgel silica microsphere lasing at 2.0μm is reported. Microspheres with different Tm3+ concentrations are fabricated by overlaying different Tm3+ concentration solgel solutions on the surface of a pure silica microsphere resonator and then annealing the sample with a CO2 laser. Based on a traditional fiber taper-microsphere coupling method, single and multimode microsphere lasing in the wavelength range 1.8-2.0μm is observed if an 808nm laser diode is used as a pump source. A relatively low threshold pumping power of 1.2mW is achieved using this arrangement. This solgel method allows for an easy varying of the Tm3+ doping concentration. The observed laser output shifts to longer wavelengths when the Tm3+ doping concentration increases. This has been explained by the larger Tm absorption at shorter wavelengths. The ability to fabricate solgel co-doped silica glass microlasers represents a new generation of low threshold and compact infrared laser sources for use as miniaturized photonic components for a wide range of applications, including gas sensing and medical surgery.

Kinetically Doped Silica Sol–Gel Optical Biosensors: Expanding Potential Through Dip-Coating

Kinetic doping has previously been shown to be an effective method of doping silica sol–gel thin films with an enzyme to construct biosensors. Until now, kinetic doping has only been applied to films produced through the spin-coating method. In this study, we present the use of dip-coating to produce thin films kinetically doped for biosensor development. In this way, kinetically doped biosensors may benefit from the increased range of substrate material shapes and sizes that may be easily coated through dip-coating but not spin-coating. The biosensors produced through dip-coating continue to show enhanced performance over more conventional enzyme loading methods with horseradish peroxidase and cytochrome C samples, showing an increase of 2400× and 1300× in enzyme concentration over that in their loading solutions, respectively. These correspond to enzyme concentrations of 5.37 and 10.57 mmol/L all while preserving a modest catalytic activity for the detection of hydrogen peroxide by horseradish peroxidase. This leads to a 77% and 88% increase in the total amount of horseradish peroxidase and cytochrome C, respectively, over that from coating the same glass coverslip via spin-coating methods.

High Efficiency Raman Lasers Based on Zr-Doped Silica Hybrid Microcavities

Raman lasers form a particularly unique and versatile class of optically pumped laser. Because they rely on stimulated Raman scattering (SRS), which is governed by the vibrational frequency of the gain material and not electronic transitions, the emission wavelength is determined by the pump wavelength, enabling broad tunability. Ultrahigh quality factor (Q) silica optical resonators are an ideal platform for Raman lasers because the long photon lifetime results in large circulating optical intensities. Previous work has demonstrated extremely low thresholds using these devices. However, only moderate Raman lasing efficiencies have been achieved in silica devices. In the present work, we demonstrate that a zirconium (Zr)-doped silica sol–gel coating can improve the performance of a silica microcavity Raman laser. Several concentrations of Zr-doped sol–gel are synthesized. The intrinsic Raman gain of the Zr-doped silica is measured using Raman spectroscopy, and the values show a clear dependence on Zr dopa...

3D magneto-photonic crystal made with cobalt ferrite nanoparticles silica composite structured as inverse opal

Three dimensional magneto-photonic crystals were realized by a low temperature sol-gel method. Self-assembled polystyrene direct opals were impregnated by CoFe2O4 nanoparticles doped silica sol-gel solution. The silica composite inverse opal structure was then created by dissolving original polystyrene photonic crystal structure using ethyl acetate. Ellipsometric and magneto-optical measurements carried-out on silica-doped monolayers evidence that the amount of nanoparticles in the matrix can reach 39%. Scanning electron microscope images of inverse opals confirm that a 3D arrangement is obtained. Transmittance measurements show a combination of photonic band gaps with the absorption of the nanoparticles. The central positions of these band gaps are in accordance with the diameter of the initial spheres through the Bragg law. Finally, non-reciprocal magneto-optical effect is demonstrated in the inverse opals through a Faraday effect hysteresis loop. It proves the ability of the method to produce magneto-photonic crystal materials.

Time evolution of samarium doped silica sol–gel materials followed by optical spectroscopy

Sol–gel preparation conditions and optical spectra between 220 and 900 nm of Sm3+ doped silica materials are discussed. It is demonstrated that the intensity of the O2− → Sm3+ charge transfer transition at 285 nm depends on gelation conditions due to samarium related defects in the silica matrix. The room temperature sol–gel transformation and drying of Sm3+ doped samples is followed using UV/Vis spectroscopy. The rate of densification of samarium doped silica materials at room temperature is calculated from increase of the intensity of Sm3+ f–f absorption transitions during time.

Adsorption of Cd(II) by Sol-Gel Silica Doped with N-(dipropylcarbamothioyl)thiophene-2-carboxamide

Sol-gel silica was doped with N,N-(dipropylcarbamothioyl) thiophene-2-carboxamide to investigate the sorption of cadmium (Cd) ions from aqueous media. In doped sol-gel silica, the large reagent molecules entrap into pores, whereas, small metal ions diffuse into pores where they make complex with doped reagent. This complexation can be accomplished by either ion exchange or chelation. Doped sol-gel sorbent was applied for removal of Cd(II) from aqueous solution in our study. Adsorption kinetics, adsorption isotherm, equilibration time, effect of initial concentration of adsorbate, and pH effect on the metal removal were studied to optimize the conditions. The prepared adsorbent shows rapid equilibrium and high stability toward high temperature and applied medium. In addition, desorption of metal ions was carried out by 1 M HCl and, thereafter, sol-gel silica adsorbent was regenerated and reused periodically.

Corrosion resistance performance of cerium doped silica sol–gel coatings on 304L stainless steel

The aim of this work is the synthesis and investigation of silane based organic–inorganic hybrid coatings, which can be used to improve the corrosion performance of steel structures subjected to a marine environment. The silane based sol–gel coatings were prepared by dip coating 304L stainless steel in a solution of organically modified silica sol made through hydrolysis and condensation of 3-glycidoxypropyl-trimethoxysilane (GPTMS) as precursor and bisphenol A (BPA) as a cross-linking agent in an acid catalyzed condition. The influence of the addition of cerium and the use of bisphenol A as a cross-linking agent on the microscopic features and morphology as well as on the corrosion resistance of the coatings were examined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), neutral salt spray tests, potentiodynamic polarization and electrochemical impedance techniques. Results show that cerium modified nano-hybrid coatings exhibit a superior corrosion inhibition performance to that displayed by silica hybrid coatings. Additionally, data showed that the bisphenol A as a cross-linking agent has a significant effect on the morphology and corrosion resistance of the cerium doped silica coating. Omitting the use of bisphenol A causes the creation of defects/cracks in the coating, thereby promoting diffusion of the aggressive electrolyte toward the substrate and decreasing the corrosion resistance of the coating.

A disposable amperometric immunosensor for chlorpyrifos-methyl based on immunogen/platinum doped silica sol–gel film modified screen-printed carbon electrode

A disposable amperometric immunosensor for sensitive detection of chlorpyrifos-methyl (CM) has been developed by combining dual signal amplification of platinum colloid with an enzymatic catalytic reaction. The immunosensor was fabricated by modification of the screen-printed carbon electrodes (SPCE) with nanocomposites made by skillful doping of bovine serum albumin conjugated chlorpyrifos-methyl antigen (BSA-Ag) and platinum colloid into silica sol–gel. The scanning electron microscope (SEM) images and electrochemical measurements showed that platinum colloid domains in the nanocomposite material could enhance electron transfer and change the brittleness of the silica sol–gel. The immobilisation of BSA-Ag on the nanocomposite retained its immunoactivities, which allowed the immobilised BSA-Ag to effectively capture unbound Ab-HRP in the detection solution. A linear response to CM concentration was exhibited, ranging from 0.4 to 20ng/mL. Detection of CM with the presented method in soil or grape samples treated with CM matched the reference values well, which indicated that the proposed disposable immunosensor hold promising applications in environmental and food monitoring.

TiO2, ZnO and nanobimetallic silica catalyzed photodegradation of methyl green

The present works describes a method for degradation and decolorization of methyl green (MG) on semiconducting oxides and nanobimetal (Ag/Pt) doped silica sol–gel powder by using UV and solar light. Bimetallic nanoparticles are the recent research interest because of the high catalytic activity and tunable surface plasmon resonances. In this study the nanobimetal (Ag/Pt) doped silica sol–gel powder were prepared and characterized. Silica sol–gel powder was characterized by FT-IR spectroscopy, SEM with EDX, TEM, DRS and XRD analysis. The results of photodegradation of methyl green on TiO2, ZnO and nanoAg/Pt bimetal doped silica sol–gel powder were presented and compared.

Photoinduced degradation of fluorescence and formation of copper nanoparticles in sol–gel silica doped with flavins

Copper nanoparticles were formed by photoirradiation of doped sol–gel silica, which was prepared by mixing Cu2+ ions, ethylenediaminetetraacetic acid (EDTA), and riboflavin into sol–gel solutions of tetramethoxysilane. The doped silica exhibited broad absorption bands at 442nm due to riboflavin and 740nm due to Cu2+-EDTA complexes. After photoirradiation, the sol–gel silica showed a reddish brown color and the absorption peak around 580nm due to the plasmon band of copper nanoparticles. Copper nanoparticles were also formed from other sol–gel silica doped with lumichrome or lumiflavin. The photostability of the flavins dyes obtained from the fluorescence intensities was in the order of lumichrome>lumiflavin>riboflavin in the sol–gel silica without Cu2+ ions. On the other hand, the fluorescence intensities were considerably reduced by photoirradiation of the sol–gel silica doped with Cu2+ ions, irrespective of the flavin dyes doped. Considering the absorption and fluorescence spectral changes during the photoirradiation, we concluded that copper nanoparticles are produced by the photoinduced electron transfer from the flavin dyes in the sol–gel silica.

Post annealing immersion: A new technique for studying rare earth ions in porous materials

A novel technique is introduced for studying how rare earth ions are incorporated into the matrix of porous materials. Tb 3 + -doped silica sol-gel is annealed to form porous glass and immersed in an aqueous Gd(NO 3 ) 3 solution. Re-heating removes the liquid and deposits Gd 3+ ions on the internal pore surfaces. Spectroscopic investigation of Gd 3+ → Tb 3+ energy transfer yields information about the location of Tb 3+ dopant ions relative to pore surfaces. Results from post-annealing immersion experiments indicate that most Tb 3+ dopant ions are close to pore surfaces when sol-gel glass is annealed to 700 °C. The observed energy transfer decreases with higher annealing temperatures, indicating that Tb 3+ dopants in densified regions are isolated from Gd 3+ ions deposited on pore surfaces. Al 3+ co-doping affects both the overall sample density and the degree of Gd 3+ → Tb 3+ interaction in post-annealing immersion samples.

Local symmetry and Z-scan analysis of ZnSe/Eu3+ doped sol–gel silica hosts

Vibrational state side-band spectral analysis of silica matrices, doped with ZnSe/Eu3+ ions, associated with the excitation transition 7F0→5D2 is used to analyze the local asymmetry of the rare earth ions in the glass host. The large inhomogeneous linewidth for the ZnSe co-doped samples indicates the wide distribution of the Eu3+ ions in the matrix and is related to the flexibility of the local glass network. The fluorescence spectra reveal that the intensity of the characteristic emission of europium increases considerably in the presence of ZnSe particles. This phenomenon can be explained by the energy transfer resulting from electron–hole recombination in the ZnSe to the rare earth ion. Nonlinear optical absorption of the sample is also investigated at a wavelength of 532 nm, using open aperture Z-scan technique. The sample exhibits reversible saturable absorption (RSA), which is found to depend on excitation fluence. RSA is due to the enhanced absorption resulting from the electron dynamics in nano-crystallites.

Luminescence and X-ray Diffraction Studies of Rare Earth Doped Silica Sol-Gel Glass

We present recent work exploring the effects of aluminum co-doping on the luminescent properties of rare earth ions in sol-gel glasses. Using x-ray diffraction techniques we have identified the formation of aluminum rich nano-crystals in silica glass annealed to high temperatures. We discuss implications of these results in understanding the impact aluminum co-doping has on rare earth luminescence in sol-gel glass.

Effect of reducing sintering atmosphere on Ce-doped sol–gel silica glasses

Abstract The effect of sintering atmosphere on the optical and structural properties of Cerium doped sol–gel silica was investigated. Two sets of xerogels with Ce concentration from 0 to 10 mol% were prepared and densified in different conditions. The effect of a post-densification rapid thermal treatment was also considered. Optical absorption measurements evidenced that in oxidizing conditions Cerium is preferably incorporated inside the silica matrix as Ce4+ while the trivalent state is favoured by reducing conditions. Transmission electron microscopy images show rare-earth clusters formation whose nature was investigated by means of Raman, EDS and microdiffraction measurements. In order to evaluate the efficiency of the glasses as scintillating materials radio-luminescence measurements were carried out. A numerical fit of RL spectra showed the presence of two components peaking at 2.7 and 3.1 eV. After RTT, the relative intensity of the 3.1 eV component increases with Ce concentration.

Microwave studies on the dielectric properties of Sm3+ and Sm3+/CdTe doped sol–gel silica glasses

Abstract Complex permittivity and conductivity studies of Samarium and Samarium/semiconductor cadmium telluride sol–gel silica glass samples were done. We use cavity perturbation technique at S band frequencies using TE 10p Mode. Structural evolution of the matrix on annealing is discussed based on FTIR analysis/XRD power diffraction. In cavity perturbation technique dielectric parameters like complex permittivity and conductivity are determined by measuring changes in resonant frequency due to small perturbation inside the cavity produced by the introduction of the samples. The addition of the semiconductor along with the samarium was found to lower the permittivity, loss factor and conductivity. Variations of permittivity values with annealing temperature find applications in IC Technology, optic fibre communication, etc. The Sm 3+ /CdTe doped glasses can also be used in the fabrication of new and improved materials for microwave electronic circuits and in electromagnetic shielding devices.

An Active Core Fiber-Optic Temperature Sensor Using an Eu(III)-Doped Sol-Gel Silica Fiber as a Temperature Indicator

An active core fiber-optic temperature sensor has been developed by using an Eu(III)-doped sol-gel silica fiber as a temperature indicator and has been tested for sensing temperature in the range from 80 degC to 500 degC. The fluorescence of Eu(III) doped inside the sol-gel silica fiber was excited with a simple LED with peak wavelength at 420 nm and the fluorescence intensity was recorded as a sensing signal. The fluorescence intensity decreases with the increase of temperature. In the temperature range from 140 degC to 300 degC, the attenuation of the fluorescence intensity of the fiber-optic sensor in decibel has a linear relationship with temperature