Silver-doped Glass Research Articles

Homogenous silver-doped nanocomposite glass

Silver nanoparticles are generated in glass by a dry process. First silver ions are driven into the glass by electric field-assisted ion exchange. Subsequent annealing in air led to the formation of silver nanoparticles beneath the surface of the glass. A thin slice of the cross section of the sample was prepared. This visualization of the depth profile facilitated optical analysis of the embedded layer containing silver nanoparticles to be preformed. We observed that there were narrower plasmon bands close to the sample surface and wider plasmon bands in lower layers. It is attributed to the formation of larger nanoparticles with lower number density close to the surface and slightly smaller nanoparticles with higher number density in the depth of the sample.

Laser-induced radial birefringence and spin-to-orbital optical angular momentum conversion in silver-doped glasses

Samples of Ag+/Na+ ion-exchanged glass that have been subject to intense laser irradiation may develop novel optical properties, as a consequence of the formation of patterns of silver nanoparticles and other structures. Here, we report the observation of a laser-induced permanent transverse birefringence, with the optical axis forming a radial pattern, as revealed by the spin-to-orbital angular momentum conversion occurring in a probe light beam. The birefringence pattern can be modeled well as resulting from thermally-induced stresses arising in the silver-doped glass during laser exposure, although the actual mechanism leading to the permanent anisotropy is probably more complex.

Radiophotoluminescence from silver-doped phosphate glass

Abstract Glass dosimeter utilizing radiophotoluminescence (RPL) is one of accumulation type solid state dosimeters, which is based on luminescence phenomenon of silver (Ag + ions)-doped phosphate glass exposed to ionizing radiation. In this study, to clarify the emission mechanism of yellow and blue RPL peaks, optical properties of Ag + -doped glass, such as optical absorption spectrum, RPL excitation spectrum before and after X-ray irradiation as well as the lifetime of both RPL peaks are measured. From the results, we discuss the emission mechanism of yellow (peaked at 2.21 eV) and blue (peaked at 2.70 eV) RPL using a proposed energy band diagram for RPL emission and excitation in Ag + -doped phosphate glass. It is found that the radiative lifetime of blue RPL is three orders of magnitude faster than that of yellow RPL.

Preparation and characterization of antibacterial P2O5–CaO–Na2O–Ag2O glasses

60P₂O₅-20CaO-(20-x) Na₂O-xAg₂O and 60P₂O₅-30CaO-(10-x) Na₂O-xAg₂O glasses, x = 0, 0.5,1, and 2 mol % were prepared using normal glass melting technique. The antibacterial activity of pressed disks of powdered glass (undoped and silver-doped glass) was investigated against S.aureus, P.aeruginosa, and E.coli micro-organisms using agar disk-diffusion assays at 37 °C for 24 h. The antibacterial activity was deduced from the inhibition zone diameter (IZD), zone of no bacterial growth, measured under the stated experimental conditions. The antibacterial activity increases with the increase in IZD and vice versa. Dissolution of glass in water at 37 °C, pH changes of water during glass dissolution, and concentrations of silver ions released from silver-doped glasses into water during their dissolution were determined. An increase in the concentration of silver ions released from silver-doped glasses into water was observed with increasing time of glass dissolution and with increasing Ag₂O content. The tested silver-free and silver-doped glasses demonstrated different antibacterial activity against the tested micro-organisms. For silver-free glasses, an increase in IZD was observed with the increase in the glass dissolution rate and with the decrease in pH of water. Also, the IZD showed an increase with increasing Ag₂O content of silver-doped glasses.

Study on the preparation and properties of silver-doped phosphate antibacterial glasses (Part I)

Silver-doped phosphate antibacterial glasses were prepared by the melting method. The antibacterial effects of some undoped and silver–doped glasses of compositions 65P 2O 5–10CaO–(25– x) Na 2O, 70P 2O 5–20CaO–(10– x) Na 2Oand (70– x) P 2O 5–30CaO, (where x = 0, 0.5, 1.2 Ag 2O), against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli micro-organisms using agar disk-diffusion assays were investigated. The structures of some glasses were studied by XRD, FT-IR, and UV–VIS spectroscopy. The variation of pH with dissolution rate was studied. The tested silver-free and silver-doped glasses demonstrated different antibacterial effects against the tested micro-organisms. For silver-free glasses, an increase in inhibition zone diameter (zone of no bacterial growth) was seen with the decrease in water pH. Silver-doped glasses showed an increase in inhibition zone diameter with increasing Ag 2O content. The low pH produced by glass dissolution was certainly a critical factor for glass antibacterial effect. The more the phosphate ions released the lower is the pH and the greater the antibacterial effect.

Environmental Radiation Monitoring Using Radiophotoluminescence in Silver-Doped Phosphate Glass

Optical properties such as optical absorption and radiophotoluminescence (RPL) spectra of silver (Ag+)-doped phosphate glass before and after x-ray irradiation were investigated in this study. It is found that the RPL spectrum consists of two emission bands which are peaked at 2.70eV (460nm blue emission) and 2.21eV (560nm yellow emission). It is also found that RPL emission intensity gradually increases with x-ray irradiation dose. From the results it is suggested that origin of each 460nm and 560nm RPL emission band is ascribed to Ag0 ion and Ag2+ ion, respectively, which are produced by x-ray irradiation. The application of the RPL phenomenon in Ag-doped phosphate glass to the environmental natural radiation monitoring is also demonstrated.

Modifications in silver-doped silicate glasses induced by ns laser beams

Glass layers for planar light waveguides prepared by Ag–Na ion exchange of different silicate glasses in molten salt baths are annealed and/or irradiated with a laser beam in the UV region, with different energy density values and total pulse numbers. The samples are mainly characterized by optical absorption spectroscopy, luminescence spectroscopy, and Rutherford backscattering spectrometry, in order to determine the role of irradiation parameters and of the host matrix structure in the aggregation phenomena. Photoluminescence spectroscopy gave information regarding the presence of Ag multimeric aggregates, the primal seeds for the growing (nano)crystals. The appearance of the plasmon resonance band in the optical absorption spectra proved the formation of Ag clusters and allowed the evolution steps of the clusterization process to be followed as a function of the energy deposited during the laser irradiation.

Evolution of the optical properties of a silver-doped phosphate glass during thermal treatment

Abstract The optical properties of a silver-doped phosphate glass have been monitored during thermal processing at several fixed temperatures by in situ optical microspectroscopy. Silver nanoparticle (NP) formation and growth processes were assessed by analysis of surface plasmon resonance spectral features. Nucleation and growth processes were distinguished, which appeared temperature and time dependent. While nucleation was favored at low temperatures, relatively high temperatures promoted NP growth by silver diffusion. Photoluminescence spectra acquired along with optical absorption data indicated a continuous reduction of Ag+–Ag0 pairs concomitant with NP precipitation, suggesting their role as nucleation centers. The work of Ag NP formation and the activation energy for silver diffusion were estimated.

Gamma rays induced defect centers in phosphate glass for radio-photoluminescence dosimeter

Abstract Gamma induced defect centers of undoped phosphate glasses and the influence of these centers on the sensitivity and build-up time of silver-doped phosphate glasses were investigated. According to the ratio of oxygen and phosphorus ions (O/P) in phosphate glass, the basic glasses were polyphosphate glass (O/P = 3.07), metaphosphate glass (O/P = 3) and ultraphosphate glass (O/P = 2.93). Concentration of Ag + was 2 mol%. Defect centers induced by gamma rays of three base glasses were detected by Electron paramagnetic resonance (EPR) and optical absorption spectra. Three kinds of defect centers were observed and the characteristics of the hyperfine splitting doublets were quite similar in these glass samples. All the defect centers are phosphorus and oxygen related radiation-induced hole trapped defect centers (POHC) and electron centers PO 3 2 − and PO 4 4− . Based on EPR and optical absorption spectra, polyphosphate glasses have the highest relative POHC concentration. The fluorescence spectra and EPR spectra of silver-doped glasses were measured. The results indicate that polyphosphate glasses have the highest sensitivity and shortest build-up time of three silver-doped phosphate glasses which are related to the concentration of POHC.

Interfacial Effects in the Relaxation Dynamics of Silver Nanometal-Glass Composites Probed by Transient Grating Spectroscopy

Relaxation dynamics of silver nanoparticles (NPs) embedded in glass have been studied by picosecond time-resolved transient grating (TG) spectroscopy. Phosphate-based glasses were prepared by melting and heat-treatment processes by which two different nanometal-glass composites were produced. The first is a glass system containing silver and tin in which Ag NPs are embedded in the matrix upon heat treatment. The second is a heat-treated silver-doped glass with spectroscopic indications of Ag+–Ag0 pairs located at or near the surface of the NPs. The time evolution of the light-induced TG for the Ag/Sn-doped glass shows an uncommon relaxation on the nanosecond time scale. Such behavior is explained in terms of energy transfer processes between polaronic and/or excitonic states in the near-interface region of the glass matrix and the NPs. In contrast, a faster monotonic relaxation is observed for the Ag-doped nanocomposite. This result is attributed to Ag NP → Ag+–Ag0 plasmon resonance energy transfer.

Photoluminescence via plasmon resonance energy transfer in silver nanocomposite glasses

This paper reports the first spectroscopic demonstration of photoluminescence (PL) owing to plasmon resonance energy transfer (PRET) from silver nanoparticles (NPs) to luminescent species in glass. Optical absorption and PL spectroscopy experiments performed on the melt-quenched silver-doped glass indicate the presence of single Ag+ ions, Ag+–Ag+ and Ag+–Ag0 pairs, and Ag NPs. After thermal processing of the material, nonradiative energy transfer from the Ag+–Ag0 luminescent centers to Ag NPs is observed by uniform suppression of band emission and the vanishing of the excitation band associated. Furthermore, evidence for PRET is observed after glass heat treatment by the appearance of a new excitation band near the surface plasmon resonance peak of Ag NPs at about 420 nm, when emission of silver pairs is monitored around 550 nm. In fact, excitation at 420 nm leads to a band emission centered around 530 nm indicating that the excitation of luminescent silver species indeed takes place via PRET. The luminescence is interpreted as arising from a Ag NP→Ag+–Ag0→Ag+–Ag+ energy transfer scheme.

Assessment of antimicrobial microspheres as a prospective novel treatment targeted towards the repair of perianal fistulae

None of the proposed materials tested for the management of perianal fistulae has proven to be a definitive treatment. To assess a new repair scaffold and drug delivery device conceived to target perianal fistula repair. Poly(D,L-lactide-co-glycolide) porous microspheres containing either antibacterial silver-releasing degradable phosphate glass or metronidazole were prepared using thermally induced phase separation. Ion- and drug-release profiling of the microspheres revealed continued release of silver ions from microspheres filled with silver-doped phosphate glass and high encapsulation efficiency for metronidazole [78% and 82% for microspheres loaded with 2.5% and 1.3% (w/w), respectively]. Microbicidal activity was confirmed by growth inhibition of bacterial species (Staphylococcus aureus, Escherichia coli and Bacteroides fragilis), which characteristically dominate the colonization of perianal fistula tracts. Microspheres containing >3 mol% silver or metronidazole resulted in strong bacterial inhibition/kill against B. fragilis; the presence of one sphere containing >3 mol% silver had a potent inhibitory effect against all the microbes studied. Microspheres became rapidly integrated with host tissue following subcutaneous implantation into a rodent wound model. The study demonstrates a novel scaffold for guided tissue regeneration providing local release of antimicrobial agents sufficient to counter bacterial colonization and warrants further investigation.

Effect of Silver-Doped Phosphate-Based Glasses on Bacterial Biofilm Growth

Silver-containing phosphate-based glasses were found to reduce the growth of Pseudomonas aeruginosa and Staphylococcus aureus biofilms, which are leading causes of nosocomial infections. The rates of glass degradation (1.27 to 1.41 microg.mm(-2).h(-1)) and the corresponding silver release were found to account for the variation in biofilm growth inhibitory effect.

Spectral Change in Silver-Doped Sodium-Borate Glass by Using Femtosecond Laser Irradiation

Spectral Change in Silver-Doped Sodium-Borate Glass by Using Femtosecond Laser Irradiation

Photoluminescence of atomic gold and silver particles in soda-lime silicate glasses

We report the chemistry and photophysics of atomic gold and silver particles in inorganicglasses. By synchrotron irradiation of gold-doped soda-lime silicate glasses we could create andidentify unambiguously the gold dimer as a stable and bright luminescing particle embedded inthe glassy matrix. The gold dimer spectra coincide perfectly with rare gas matrix spectra ofAu2. The glass matrix is, however, stable for years, and is hence perfectly suitedfor various applications. If the irradiated gold-doped sample is annealed at550 °C a bright green luminescence can be recognized. Intense 337 nm excitation inducesa decrease of the green luminescence and the reappearance of the 753 nmAu2 emission, indicating a strong interrelationship between both luminescence centers.Time-dependent density functional theory (TD-DFT) calculations indicate that the greenluminescence can be assigned to noble metal dimers bound to silanolate centers. Thesecomplexes are recognized as the first stages in the further cluster growth process, which hasbeen investigated with small-angle x-ray scattering (SAXS). In silver-doped glasses,Ag0 atoms can be identified with electron paramagnetic resonance(EPR) spectroscopy after synchrotron activation. Annealing at300 °C decreases theconcentration of Ag1, but induces an intense white light emission with 337 nm excitation. The white luminescencecan be decomposed into bands that are attributed to small silver clusters such asAg2,Ag3 and Ag4, and an additional band matching the green emission of gold-doped glasses.

Study on the preparation and properties of silver-doped borosilicate antibacterial glass

Abstract Silver-doped borosilicate antibacterial glass was prepared by the melting method. By changing the glass composition, the slow release property of the antibacterial active composition was adjusted and the deoxidization of Ag + was restrained. The structure and properties of the glass were characterized by SEM, IRE, AAS and antibacterial ring test. The results show that the glass has excellent antibacterial, release silver and infrared radiation properties.

Antibacterial Activity of Silver-Doped Glasses and Glass-Ceramics

A glass (G) and a glass-ceramic (GC) of different composition were selected and studied to realize a biocompatible e/o bioactive material with antibacterial properties through the introduction of silver ions. The glass was produced in bulk form, instead glass-ceramic powders were sintered to abtain massive samples, which are characterized in terms of biocompatibility and subjected to ion- exchange technique [1] to allow the silver ions introduction and modify only the external surface layer of the materials, thus maintaining unchanged the bulk characteristics. The obtained samples were completely characterized to verify if the silver introduction leads to structural, morphological or in vitro behaviour change; silver release test was also carried out as well as antibacterial test with Staphylococcus Aureus and cytotoxicity test on human cells.

Micro-machinability of silver–sodium ion-exchanged glass by UV nanosecond laser

Micro-machining of silver–sodium ion-exchanged lime-sodium glass was carried out using fourth harmonic generation (FHG) of Nd:YAG nanosecond laser. The laser irradiations to silver-doped glasses produced low aspect ratio and defect-free holes because of their high-optical absorptions at the vicinity of ion-exchanged surfaces. The ablation rates (i.e. removed depth per laser shot) of ion-exchanged glasses gradually decreased with the distance from glass surfaces and were saturated, corresponding to the dilution of silver ion concentration. The ablation rates and hole shapes drastically changed when the processed hole bottoms reached the ion penetration depths. Scanning electron microscope images indicated that the walls of processed holes in non-silver-containing region had irregular-shaped and porous structures. Therefore, well-designed ion distributions were necessary for the high-accuracy fabrication of micro-components. From these results, a micro-channel and a cylindrical column-shaped cantilever were fabricated on the glass substrates.

Effect of Silver Content on the Structure and Antibacterial Activity of Silver-Doped Phosphate-Based Glasses

Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 microg x mm(-2) x h(-1)) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer ( approximately 20 microm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by (31)P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections.

The structure and properties of silver-doped phosphate-based glasses

An undoped and two silver-doped (0, 3 and 5 mol% Ag) phosphate glass compositions were investigated for their structure and properties. These compositions had in a previous study been investigated for their antimicrobial properties, and were found to be extremely potent at inhibiting the micro-organisms tested. Thermal, X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and X-ray absorption Near Edge Structure (XANES) studies were used to elucidate the structure of the compositions investigated, whilst degradation and ion release studies were conducted to investigate their properties. No significant differences were found between the T (g) values of the silver containing glasses, while XRD analysis revealed the presence of a NaCa(PO3)(3) phase. NMR showed the dominance of Q(2) species, and XANES studies revealed the oxidation state of silver to be in the +1 form. No correlation was seen between the degradation and cation release profiles observed, and the P3O93 anion was the highest released anionic species, which correlated well with the XRD and NMR studies. Overall, it was ascertained that using Ag2SO4 as a precursor, and producing compositions containing 3 and 5 mol% Ag, the levels of silver ions released were within the acceptable cyto/biocompatible range.