Silica Gel Glass Research Articles

Photoluminescence from trivalent-cerium-doped silica glass prepared by sol–gel method with aluminum co-dopant

Trivalent cerium is an important luminescent center giving light emission in short wavelength region depending on host materials. Sol–gel formed silica glass is an ideal matrix due to its high transparency, robustness, and low-temperature processability, but the emission from cerium in silica matrix is often mixed up with that from defects in the matrix, making it difficult to obtain well-determined characteristics. Bright emission from Ce ions peaking at about 400 nm was observed in sol–gel silica glasses synthesized with aluminum co-dopant. From luminescence decay time, the origin was confirmed to be d−f transition in trivalent Ce. From dependence of emission characteristics and UV absorbance on aluminum concentration, it was found that the co-dopant plays an important role to convert the optically inactive tetravalent ions to emissive trivalent state.

Characterization and enhanced nonlinear optical limiting response in carbon nanodots dispersed in solid-state hybrid organically modified silica gel glasses

Freely dispersed carbon nanodots (CNDs) were introduced into a 3-glycidoxy-propyltrimethoxysilane modified silicate gel glass (i.e. an organically modified silica or ORMOSIL) by a highly efficient and simple sol-gel process, which could be easily extended to prepare functional molecules/nanoparticles solid state optoelectronic devices. Scanning electron microscope imaging, Fourier transform infrared spectroscopy, pore structure measurements, ultraviolet–visible spectroscopy, and fluorescence spectroscopy were used to investigate the surface characteristics, structure, texture, and linear optical properties of the CND/SiO2 ORMOSIL gel glasses. Images and UV/Vis spectra confirmed the successful dispersion of CNDs in the ORMOSIL gel glass. The surface characteristics and pore structure of the host SiO2 matrix were markedly changed through the introduction of the CNDs. The linear optical properties of the guest CNDs were also affected by the sol-gel procedure. The nonlinear optical (NLO) properties of the CNDs were investigated by a nanosecond open-aperture Z-scan technique at 532 nm both in liquid and solid matrices. We found that the NLO response of the CNDs was considerably improved after their incorporation into the ORMOSIL gel glasses. Possible enhancement mechanisms were also explored. The nonlinear extinction coefficient gradually increased while the optical limiting (OL) threshold decreased as the CND doping level was increased. This result suggests that the NLO and OL properties of the composite gel glasses can be optimized by tuning the concentration of CNDs in the gel glass matrix. Our findings show that CND/SiO2 ORMOSIL gel glasses are promising candidates for optical limiters to protect sensitive instruments and human eyes from damage caused by high power lasers.

Hyperpolarized 129Xe NMR as an Alternative Approach for Investigating Structure and Transport in Ordered Mesoporous Materials Prepared via Pseudomorphic Transformation

The stepwise pseudomorphic transformation of silica gel and porous glass into MCM-41 (Mobil Composition of Matter No. 41) has been investigated for the first time with hyperpolarized 129Xe NMR. The changes in structure were followed by changes in the line shape and chemical shift of the 129Xe NMR signals, whereby variable temperature (VT)-NMR and selective 1D exchange spectroscopy (EXSY) experiments revealed differences in the mechanism of the transformation, depending on the starting material.

Characterization by optical and magnetic spectroscopy of a synthesized SiO2 thin film used for radiation detector

This work reports the synthesis and characterization of silica glass prepared by sol–gel procedure and finds out the effects of doses of gamma irradiation on the steps route of the heat-treated sample at 600 and 1100 °C. Combined characterizations of the glassy samples have been carried out by optical absorption and electron paramagnetic resonance. Also, FT infrared absorption spectra have been measured for both the heat-treated samples before and after gamma irradiation. Optical absorption spectra have identified an absorption band at 212–215 nm beside a broad band at 230–265 nm and the correlation of E′ center with heat-treatment and gamma irradiation have been followed. FT infrared absorption spectra indicate the bands within near IR region representing the vibrational modes due to water, OH and SiOH within the wavenumber range 2500–3700 cm−1 are affected by heat treatment due to the elimination of organic residue and amount of OH and water. ESR investigations confirm the results obtained from optical and FTIR measurements. It is concluded from the collective data that sol–gel silica glass can serve as acceptable candidate for gamma-rays irradiator and gamma chamber dosimetry.

Solid–solid phase transition of tris(hydroxymethyl)aminomethane in nanopores of silica gel and porous glass for thermal energy storage

To extend the use of phase change materials (PCMs) of those with good performance, tris(hydroxymethyl)aminomethane (THAM) is embedded in silica gels (SG) (pore diameter, d = 15–100 nm) and in controlled porous glasses (CPG) (nominal d = 12–100 nm). The THAM/SG and THAM/CPG composites are characterized by SEM and XRD. Latent heat storage performance of THAM/SG and THAM/CPG is investigated using differential scanning calorimetry, showing size dependence of phase transition temperature, enthalpy change and supercooling. THAM in the nanopores displays stable transition temperature and heat storage capacity in a short-term thermal cycling. The bulk and the nanosized THAM own the same diffraction patterns. The encapsulation of phase change material in nanoporous media is a promising way of tuning the thermal energy properties of those ideal PCMs for use in a wider range of temperature.

Encapsulation of cobalt porphyrins in organically modified silica gel glasses and their nonlinear optical properties

2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin Cobalt(II) (CoPor) was introduced into nanostructured organically modified silica (ORMOSIL) using a sol–gel technique. Scanning electron microscopy, Fourier transform infrared (FT-IR), thermogravimetric analysis, and UV–Vis spectroscopy were performed to investigate the morphology, structure, thermal stability, and linear optical properties of the resulting gel glasses. The FT-IR spectrum and UV–Vis spectra strongly indicated the formation of a silica gel glass network and the successful encapsulation of CoPor in ORMOSIL silica gel glasses, respectively. The introduction of guest CoPor molecules induces silica to form more condensed surface characteristics, owing to the fact that CoPor can promote the hydrolysis and polycondensation procedure, and hence have better thermal stability as compared to blank silica gel glasses. Meanwhile, the dimerization phenomenon in a liquid matrix can be effectively suppressed in a silica solid-state matrix and is attributed to the ‘cage protection effect.’ The nonlinear optical (NLO) properties of CoPor gel glasses were investigated using the open-aperture Z-scan technique at 532 nm. The NLO performance of CoPor-incorporated solid-state silica gel glasses has been improved in comparison with those dispersed in dimethylformamide solution. More significantly, the NLO properties of CoPor-doped ORMOSIL gel glasses can be controlled by adjusting the concentration of the CoPor molecules.

Cerium-activated sol–gel silica glasses for radiation dosimetry in harsh environment

Cerium-doped silica glass has been prepared for ionizing radiation dosimetry applications, using the sol–gel route and densification under different atmospheres. In comparison with the glass densified under air atmosphere, the one obtained after sintering the xerogel under helium gas presents improved optical properties, with an enhancement of the photoluminescence quantum yield up to 33%, which is attributed to a higher Ce3+ ions concentration. Such a glassy rod has been jacketed in a quartz tube and then drawn at high temperature to a cane, which has been used as active material in a fibered remote x-ray radiation dosimeter. The sample exhibited a reversible linear radioluminescence intensity response versus the dose rate up to 30 Gy s−1. These results confirm the potentialities of this material for in vivo or high rate dose remote dosimetry measurements.

Structure and optical properties of transparent Er3+-doped CaF2–silica glass ceramic prepared by controllable sol–gel method

Transparent Er3+-doped CaF2–silica glass ceramics were prepared by the direct physical introduction of Er3+ doped CaF2 nanocrystals into acid-catalyzed sol–gel silica glass. The physical methods of ball milling, ultrasonic baths, and stirring were investigated to disperse Er3+ doped CaF2 nanocrystals in the silica sols. The CaF2–silica sol mixture went through gelation and heat-treatment to form Er3+-doped CaF2–silica glass ceramics. The morphology of Er3+ doped CaF2 in silica glass did not change after heat-treatment at 600°C for 10h. The experimental results showed that Er3+ doped CaF2 in the glass ceramic prepared with the assistance of ball milling possesses the best dispersity and homogeneity. The highest in-line transmittance of the glass ceramic reached up to 85% in visible region. Glass ceramic exhibits efficient up-conversion emissions corresponding to the Er3+:4F9/2→4I15/2 transition and long lifetime of 4F9/2 level (1.73ms) under 980nm excitation.

Self-assembly of cadmium metasilicate nanowires as a broadband optical limiter

Cadmium metasilicate nanowires (CdSiO3 NWs) have been synthesized through a facile, eco-friendly, low-cost water–ethanol mixed-solution hydrothermal route. The transmission electron microscopy measurements of as-prepared samples indicate that the CdSiO3 NWs with diameters in the range of 10–60nm and lengths of more than 1μm were constructed by self-assembly of 5–10-nm CdSiO3 nanoparticles with good crystallinity. The monoclinic phase formation of the sample is studied in detail by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermo gravimetric analysis. The results indicate that a pure monoclinic phase of CdSiO3 can be obtained by a hydrothermal route without further calcinations and SiO4 tetrahedra were the main constituents of the CdSiO3 NWs. The nanosecond optical limiting (OL) effects were characterized by using an open-aperture (OA) Z-scan technique with 4-ns laser pulses at both 532 and 1064nm. Theses CdSiO3 NWs displayed an excellent OL performance at 532 and 1064nm, which was better than carbon nanotubes, a benchmark optical limiter. Input-fluence dependent scattering measurements suggested than nonlinear scattering played an important role in the observed optical limiting behavior in CdSiO3 NWs at 532 and 1064nm. More significantly, the NLO performance in CdSiO3 NWs incorporated solid silica gel glass has been improved in comparison to those dispersed in water. The unique structure and excellent OL property render these CdSiO3 NWs competitors in the realms of optical limiting applications.

Colloidal quantum-dot-based silica gel glass: two-photon absorption, emission, and quenching mechanism.

Two-photon (TP) three-dimensional solid matrices have potential applications in high density optical data reading and storage, infrared-pumped visible displays, lasers, etc. Such technologies will benefit greatly from the advantageous properties of TP materials including tunable emission wavelength, photostability, and simple chemical processing. Here, this ideal TP solid is made possible by using a facile sol-gel process to engineer colloid quantum dots into silica gel glass. Characterization using an open-aperture Z-scan technique shows that the solid matrices exhibited significant TP optical properties with a TP absorption coefficient of (9.41 ± 0.39) × 10(-2) cm GW(-1) and a third-order nonlinear figure of merit of (7.30 ± 0.30) × 10(-14) esu cm. In addition, the dependence of the TP properties on high-temperature thermal treatment is studied in detail to obtain a clear insight for practical applications. The results illustrate that the sample can maintain stable TP performance below the synthesis temperature of the CdTe/CdS colloidal quantum dots. Furthermore, the mechanisms for thermal quenching of photoluminescence under different temperature regimes are clarified as a function of the composition.

Investigation of bioactivity, biocompatibility and thermal behavior of sol–gel silica glass containing a high PEG percentage

SiO2/PEG organic–inorganic hybrid materials, which contain 60 or 70 weight percentage of PEG, were synthesized by the sol–gel technique. The materials were characterized and subjected to various tests to assess their application in the biomedical field. The evaluation of their morphology by scanning electron microscopy (SEM) confirms the homogeneity of the samples on the nanometer scale. Fourier transform infrared spectroscopy (FT-IR) indicated that the two components of the hybrids (SiO2 and PEG) are linked by hydrogen bonds. This feature makes them class I hybrids. Simultaneous thermogravimetry/differential thermal analysis (TG/DTA) was used to investigate their thermal behavior and to establish the best temperatures for their pre-treatment. The fundamental properties that a material must have to be used in the biomedical field are biocompatibility and bioactivity. The formation of a hydroxyapatite layer was observed on the hybrid surface by SEM/EDX and FTIR after soaking in simulated body fluid. This indicates that the materials are able to bond to bone tissue. Moreover, the biocompatibility of SiO2/PEG hybrids was assessed by performing WST-8 cytotoxicity tests on fibroblast cell NIH 3T3 after 24h of exposure. The cytotoxicity tests highlight that the cell viability is affected by the polymer percentage. The results showed that the synthesized materials were bioactive and biocompatible. Therefore, the results obtained are encouraging for the use of the obtained hybrids in dental or orthopedic applications.

Effect of annealing and dopants concentration on the optical properties of Nd3+:Al3+ co-doped sol–gel silica glass

Nd3+ in SiO2 glass samples co-doped with aluminum at different concentrations have been synthesized by a sol–gel method. The effect of annealing temperature and concentration of dopants on the optical properties of the samples were investigated. Red-shift in absorption peaks was observed with annealing. Judd–Ofelt analysis shows the change in local environment of the Nd3+ ions with heat treatment. The fluorescence intensity of peaks at 880nm and 1060nm which result from the 4F3/2 →4I9/2 and 4I11/2 states increased significantly with increase in annealing temperature as well as aluminum concentration.

Aluminum effects on structure and spectroscopic properties of holmium-doped sol–gel silica glasses

A series of Ho3+-doped silica glasses containing different Al2O3/Ho2O3 mole ratios were prepared successfully using a sol–gel method combined with high temperature sintering. The X-ray diffraction (XRD), nuclear magnetic resonance (NMR) spectra of 27Al, and X-ray photoelectron spectra (XPS) of O1s, as well as the absorption and fluorescence spectra of the Ho3+ ions in these silica glasses, were recorded and analyzed systematically. The 27Al-NMR spectral studies indicated that Al3+ ions entered the glass structure mainly in sixfold and fivefold co-ordination for the series of sol–gel HAS glasses with constant 0.2 mol% Ho2O3 content. The NMR and XPS results obtained indicated a relationship between the amounts of Al2O3 and Ho2O3 and the Al coordination. Based on the structure and spectroscopic properties of the Ho3+-doped silica glasses, it was concluded that the optimum Al2O3/Ho2O3 mole ratio for the Ho3+/Al3+ co-doped silica glass for a 2-μm laser was 15.

Facile Method of Preparing Highly Luminescent Silica Gel Glass Incorporating Hydrophobic Semiconductor Quantum Dots

A facile method for preparing highly luminescent silica gel glass incorporating hydrophobic quantum dots (QDs) has been presented. The prepared glass showed excellent optical properties such as good transparency, high stability, and efficient luminescence. QDs with different crystal structures showed distinct behaviors when embedded into a silica matrix. QDs with zincblende structure showed better optical properties than that of wurtzite QDs. The luminescence efficiency of silica gel glass incorporating zincblende QDs reached up to 50%, same as the initial values in solution.

Role of Optical Fiber Drawing in Radioluminescence Hysteresis of Yb-Doped Silica

Point defects in the host lattice of a scintillator material can trap carriers, slowing down their migration or even preventing their transfer to luminescent centers. Such competition schemes between defects and luminescent centers may explain also the hysteresis effect, which consists of a progressive enhancement of scintillation efficiency with accumulated dose. We propose a comparison between the scintillation hysteresis effect of Yb-doped sol–gel silica glasses in bulk and fiber forms, and we correlate them with traps monitored by wavelength-resolved thermally stimulated luminescence in both materials. The results demonstrate that the fiber-drawing process is responsible for modifications of the defectiveness of the glass network, with a change of the local distribution of the traps surrounding the luminescent center. The consequence of such modifications is the removal, in the fiber samples, of the thermally stimulated luminescence peak ascribed to traps closer to Yb ions and unstable at room tempera...

Spectroscopic properties of Tm3+/Al3+ co-doped sol–gel silica glass

Tm3+/Al3+ co-doped silica glass was prepared by sol–gel method combined with high temperature sintering. Glasses with compositions of xTm2O3–15xAl2O3–(100−16x) SiO2 (in mol%, x=0.1, 0.3, 0.5, 0.8 and 1.0) were prepared. The high thulium doped silica glass was realized. Their spectroscopic parameters were calculated and analyzed by Judd–Ofelt theory. Large absorption cross section (4.65×10−21cm2 at 1668nm) and stimulated emission cross section (6.00×10−21cm2 at 1812nm), as well as low hydroxyl content (0.180cm−1), long fluorescence lifetime (834μs at 1800nm), large σem×τrad (30.05×10−21cm2ms) and large relative intensity ratio of the 1.8μm (3F4→3H6) to 1.46 (3H4→3F4) emissions (90.33) are achieved in this Tm3+/Al3+ co-doped silica glasses. According to emission characteristics, the optimum thulium doping concentration is around 0.8mol%. The cross relaxation (CR) between ground and excited states of Tm3+ ions was used to explain the optimum thulium doping concentration. These results suggest that the sol–gel method is an effective way to prepare Tm3+ doped silica glass with high Tm3+ doping and prospective spectroscopic properties.

Encapsulation of graphene oxide/metal hybrids in nanostructured sol–gel silica ORMOSIL matrices and its applications in optical limiting

Abstract Optically transparent organically modified silica (ORMOSIL) gel glasses doped with graphene oxide (GO)/metal nanoparticle (NP) hybrids were synthesized using a simple sol–gel technique. The two-dimensional GO/metal NP hybrids dramatically changed the surface characteristics of silica-based gel glasses whilst maintaining their structural integrity during the sol–gel procedure. The optical limiting (OL) properties of GO/metal NP-doped ORMOSIL gel glasses were investigated using a nanosecond open-aperture Z-scan technique at 532 nm. The metal NP hybrids exhibited significantly enhanced OL performance compared with their individual counterparts in ORMOSIL gel glasses. The improvement in GO/Au NP-doped gel glasses is attributed to surface plasmon resonance, while interband transition is responsible for the enhancement in GO/Pd NP-doped gel glasses. The OL behavior of GO/metal NP-doped gel glasses were mostly attributed to the combined mechanisms of excited state absorption and nonlinear scattering.

Effect of silver ions on the energy transfer from host defects to Tb ions in sol–gel silica glass

Plasmonic metal structures have been suggested to enhance the luminescence from rare-earth (RE) ions, but this enhancement is not yet well understood or applied to phosphor materials. Although some reports using Ag nanoparticles (NPs) in glass have attributed enhancement of RE emission to the strong electric fields associated with Ag NPs, it has also been proposed that the enhancement is instead due to energy transfer from Ag ions to RE ions. Our work using sol–gel silica shows a third possibility, namely that enhancement of the RE (e.g. Tb) emission is due to energy transfer from defects of the host material to the Tb ions, where the addition of Ag influences the silica host defects. The oxidation state of Ag as a function of annealing temperature was investigated by x-ray diffraction, transmission electron microscopy, UV–vis measurements and x-ray photoelectron spectroscopy, while optical properties were investigated using a Cary Eclipse fluorescence spectrophotometer or by exciting samples with a 325nm He–Cd laser. The results showed that Ag ions have a significant effect on the silica host defects, which resulted in enhancement of the green Tb emission at 544nm for non-resonant excitation using a wavelength of 325nm.

Effects of densification atmosphere on optical properties of ionic copper-activated sol–gel silica glass: towards an efficient radiation dosimeter

Ionic copper-doped pure silica glass, with high photoluminescence (PL) quantum yield (QY), has been prepared using the sol–gel technique and densification of the porous xerogel under inert atmosphere. The optical properties of the obtained glass, and especially the green light emission due to Cu+ ions under UV excitation, have been studied and compared to those of the glass produced in air atmosphere conditions. We have shown that the sintering process under helium increases the quantum efficiency of this emission by a factor 40. Moreover, the resulting copper-doped silica rod has been used in the fabrication of a high numerical aperture microstructured optical fiber, which shows similar luminescent properties to the sol–gel preform. The obtained fiber exhibits promising characteristics to be employed in an all-fibred UV sensor. In particular, the high emission efficiency and the specific air-clad geometry of the fiber made it possible to perform measurements without removing the polymer coating.

Extraction, separation and identification of compounds from leaves of Solanum elaeagnifolium Cav. (Solanaceae)

Aim of the present study was to identify some phenolic compounds isolated from the dried powder leaves of Solanum Elaeagnifolium Cav. (Solanaceae family) collected from Benghazi area, Libya originally native in the Americas. The extraction was carried out with methanol at room temperature and treated by acidification (H2SO4, pH = 4) & basification (NH4OH, pH = 10). The compounds were separated by chromatographic method through a wet glass silica gel column and purification by medium pressure liquid chromatography (MPLC). The experiment yielded one novel compound named 2-(2-hydroxyphenoxy)-3,6,8-trihydroxy-4H-chromen-4-one [A3] and three previously known phenolic which were isolated for the first time from this plant under study (Quercetin [A1], Rutin [A2] & Mangiferin [A4]). The structures were determined using modern spectroscopic techniques (IR, EI-mass, 1H-NMR, 13C-NMR, APT, HMQC & COSY) using DMSO-d6 solvent in magnetic resonance application.DOI: http://dx.doi.org/10.3329/icpj.v3i3.17890 International Current Pharmaceutical Journal, February 2014, 3(3): 234-239