Silver-doped Phosphate Glasses Research Articles

Defect Formation by Radiation in Silver-Doped Phosphate Glasses

Defect Formation by Radiation in Silver-Doped Phosphate Glasses

Weathering and Antimicrobial Properties of Laminate and Powder Coatings Containing Silver Phosphate Glass Used as High-Touch Surfaces

Increasing the use of hygienic high-touch surfaces with antimicrobial properties in health care and public spaces is one way to hinder the spread of bacteria and infections. This study investigates the antimicrobial efficacy and surface reactivity of commercial laminate and powder coated surfaces treated with silver-doped phosphate glass as antimicrobial additive towards two model bacterial strains, Escherichia coli and Bacillus subtilis, in relation to surface weathering and repeated cleaning. High-touch conditions in indoor environments were simulated by different extents of pre-weathering (repeated daily cycles in relative humidity at constant temperature) and simplified fingerprint contact by depositing small droplets of artificial sweat. The results elucidate that the antimicrobial efficacy was highly bacteria dependent (Gram-positive or Gram-negative), not hampered by differences in surface weathering but influenced by the amount of silver-doped additive. No detectable amounts of silver were observed at the top surfaces, though silver was released into artificial sweat in concentrations a thousand times lower than regulatory threshold values stipulated for materials and polymers in food contact. Surface cleaning with an oxidizing chemical agent was more efficient in killing bacteria compared with an agent composed of biologically degradable constituents. Cleaning with the oxidizing agent resulted further in increased wettability and presence of residues on the surfaces, effects that were beneficial from an antimicrobial efficacy perspective.

Femtosecond Direct Laser Writing of Silver Clusters in Phosphate Glasses for X-ray Spatially-Resolved Dosimetry

Radio-photoluminescence in silver-doped phosphate glasses has been extensively used for X-ray dosimetry. In this paper, we present the potential of silver clusters for X-ray spatially resolved dosimetry. Those clusters are generated in phosphate glasses containing a high concentration of silver oxide by femtosecond direct laser writing technique. Two phosphate glasses of different compositions were investigated. First, the spectroscopic properties of the pristine glasses were studied after X-ray irradiation at different doses to assess their dosimetry potential. Second, the impact of X-rays on the three-dimensional inscribed silver clusters has been analyzed using several spectroscopies methods. Our analysis highlights the resilience of embedded silver clusters acting as local probes of the deposited doses. We demonstrate that these inscribed glasses can define the range and sensitivity of X-ray doses and consider the realization of spatially-resolved dosimeters.

Atomic-Scale Structural Characterization of Silver-Doped Phosphate-Based Glasses Prepared by Coacervation

Phosphate-based glasses (PBGs) are traditionally prepared using the high-temperature melt-quenching (MQ) route or via the more recent sol–gel (SG) method that requires the use of organic solvents. The coacervation method represents an excellent inexpensive and green alternative to MQ and SG, being performed in aqueous solution and at room temperature. Coacervation is particularly applicable for the production of PBGs designed for biomedical applications because it allows for the inclusion of temperature-sensitive molecules and does not require the use of toxic solvents. Whereas the atomic structure of the MQ and SGPBGs is known, the atomic structure of those prepared via coacervation has yet to be investigated. In this study, a comprehensive advanced structural characterization has been performed on phosphate-based glasses in the system P2O5–CaO–Na2O–Ag2O (Ag2O mol % = 0, 1, 3, 5, 9, and 14) prepared via the coacervation method. Glasses within this system should find application as bioresorbable biomaterials thanks to their ability to release bioactive ions in a controlled manner. In particular, they possess antibacterial properties, inferred by the release of Ag+ over time. High-energy X-ray diffraction (HEXRD), 31P and 23Na solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), and X-ray absorption Spectroscopy (XAS) at the Ag K-edge were used to probe the atomic structure of the glasses after drying in vacuum and after calcination at 300 °C. The length of the polyphosphate chains in the solid state appears to be independent of silver concentration; however, significant degradation of these chains is seen after calcination at 300 °C. Atomic-scale characterisation results indicate that the structure of these glasses is akin to that of other silver-doped phosphate glasses prepared using the MQ and SG methods. This suggests that phosphate-based glasses prepared using milder and greener conditions may have similar chemical and physical properties such as solubility, biocompatibility, and antibacterial properties.

Observations regarding the build-up effect in radiophotoluminescence of silver-doped phosphate glasses

Results are presented from measurements of radiophotoluminescence (RPL), optical absorption (OA) and electron paramagnetic resonance (EPR) on Ag-doped alkali-phosphate glass. The build-up phenomenon for RPL is followed during and after irradiation. Reversal of this build-up is induced via exposure to ultra-violet light (UV) at a wavelength of 254 nm and changes to the RPL emitting centers and the EPR spectra are followed during and after UV exposure. The experimental results indicate that Ag2+ centers may be the main centers responsible for RPL emission in the orange region of the spectrum, peaking around 630 nm. Computer simulations of the rate equations describing the suggested charge transfer processes occurring during irradiation, build-up and UV exposure qualitatively support these conclusions.

Glass-forming compositions and physicochemical properties of degradable phosphate and silver-doped phosphate glasses in the P2O5–CaO–Na2O–Ag2O system

Phosphate and silver-doped phosphate glasses are potential candidates for use as degradable biomaterials and as antibacterial materials as well. The present investigation explores the glass-forming compositions (GFC), physical properties and degradation rates of both phosphate glasses in the P2O5–CaO–Na2O ternary system and silver-phosphate glasses derived from it by introducing Ag2O in replacement of Na2O. The glasses were prepared using the traditional melting–annealing technique applied in glass making industry. Bulk glasses were prepared without using any special precautions or specific conditions (contrary to previous studies) which can prevent crystallization or segregation of silver particles from the melt. A wide glass formation domain with ≥40mol% P2O5 was determined in the ternary P2O5–CaO–Na2O system. However, up on Ag2O addition, the amount of Ag2O that can exist in the glass and remains amorphous was limited to 2mol% as ensured from X-ray diffraction (XRD). The compositions with ≥60mol% P2O5 and 0.5, 1 or 2mol% Ag2O formed transparent and colorless silver phosphate glasses. Whereas, the compositions with ≤55mol% P2O5 did not form glasses and showed immediate partial crystallization and separation of silver particles. Thereafter, the structure of representative glasses was studied by FT-IR and UV–vis absorption spectroscopy. Finally, as silver ions function as antibacterial metal ions, the amounts of silver ions released from silver phosphate glasses were measured by atomic absorption spectrometry (AAS).

A reversible fluorescent probe for monitoring Ag(I) ions.

Silver-containing nanomaterials are of interest for their antibiotic properties, for a wide range of applications from medicine to consumer products. However, much remains to be learnt about the degradation of such materials and their effects on human health. While most analyses involve measurement of total silver levels, it is important also to be able to measure concentrations of active free Ag(I) ions. We report here the preparation of a coumarin-based probe, thiocoumarin silver sensor 1 (TcAg1), that responds reversibly to the addition of silver ions through the appearance of a new fluorescence emission peak at 565 nm. Importantly, this peak is not observed in the presence of Hg(II), a common interferent in Ag(I) sensing. To establish the utility of this sensor, we prepared silver-doped phosphate glasses with demonstrated bactericidal properties, and observed the Ag(I) release from these glasses in solutions of different ionic strength. TcAg1 is therefore a useful tool for the study of the environmental and medical effects of silver-containing materials.

Laser writing of nonlinear optical properties in silver-doped phosphate glass.

The formation of both local second- and third-harmonic generations (SHG and THG) induced by a train of femtosecond laser pulses in silver-doped phosphate glasses is addressed. Based on modeling calculations, including various diffusion and kinetic processes, THG is shown to result from the formation of silver clusters. The latter organize into a ring-shape structure, leading to the emergence of a static electric field. By breaking the glass centro-symmetry, this field gives rise to a local effective second-order susceptibility, inducing SHG. Both theoretically predicted SHG and THG evolutions with respect to the number of pulses in the train are in good agreement with experimental observations. In particular, the observed reaching of a maximum in the nonlinear optical responses after a few thousands of pulses is explained by the competition of various physical processes. A cooling of the glass is shown to improve the process efficiency of the laser writing of second-order nonlinearity.

Catalyst role of Nd3+ ions for the precipitation of silver nanoparticles in phosphate glass

The present work proposes that neodymium(III) performs as catalyst enhancing the precipitation of Ag nanoparticles (NPs) in silver-doped phosphate glass. In situ optical isothermal microspectroscopy was employed for evaluating the influence of the rare-earth dopant on the kinetics of Ag NP precipitation in real time in the solid-state host. A temperature-dependent first-order exponential increase with time of the peak optical density of the surface plasmon resonance of Ag NPs was observed in relation to concomitant particle nucleation and diffusion-driven growth. An Arrhenius-type plot was used for the activation energy estimation of the plasmonic Ag particles precipitation at 2.3 eV. This value is about 56% lower than the activation energy of 5.2 eV measured previously in our group [46] for the diffusion-based Ag NP growth in the glass without Nd3+ ions. Further characterizations were performed by differential scanning calorimetry, transmission electron microscopy, solid-state 31P nuclear magnetic resonance spectroscopy, and Raman scattering, in support of the in situ optical measurements. The distinctive results were discussed in the context of glass composition and structure.

English

English

Modeling of cluster organization in metal-doped oxide glasses irradiated by a train of femtosecond laser pulses

The formation of silver cluster structures at submicrometer spatial scales under the irradiation by high-power femtosecond laser pulses with high repetition rate was observed in various glasses containing silver ions. In order to account for the formation of these structures in metal-doped glasses, we present a theoretical model for the organization of noble metallic clusters induced by a train of femtosecond laser pulses. The model includes photoionization and laser heating of the sample, diffusion, kinetic reactions, and dissociation of metallic species. This model was applied to reproduce the formation of cluster structures in silver-doped phosphate glass. The parameters of the silver structures were obtained numerically under various incident pulse intensities and number of pulses. Numerical modeling shows that the involved microscopic physical and chemical processes naturally lead to the emergence of a silver cluster organization, together with charge migration and subsequent trapping giving rise to a strong static electric field buried in the irradiated area as experimentally observed. Based on this modeling, a theoretical basis is provided for the design of new metallic cluster structures with nanoscale size.

Structural features of silver-doped phosphate glasses in zone of femtosecond laser-induced modification

Femtosecond (fs) laser writing of two-dimensional microstructures (waveguides) is demonstrated in bulk phosphate glasses doped with silver ions. Silver-content phosphate and silver-content niobium–phosphate glasses with high concentration of silver oxide 55mol% were used as samples for fs laser writing. The chemical network structure of the synthesized samples is analyzed through Raman spectroscopy and was found to be strongly sensitive to Nb incorporation. It was found that the direct laser writing process enables not only reorganization of glass network, but also formation of color centers and silver nanoparticles that are revealed in appearance of luminescence signal and plasmon absorption. The process of NPs' formation is more efficient for Nb-phosphate glass, while color centers are preferably formed in phosphate glass.

One step fabrication of glass–silver@core–shell fibers: silver-doped phosphate glasses as precursors of SERS substrates

In this study we report on the fabrication, morphological characterization, and surface enhanced Raman scattering (SERS) activity of innovative glass–silver@core–shell substrates obtained by an inexpensive and simple approach. Silver-doped glass fibers were obtained from the phosphate glass system NaH2PO4–GeO2–Al2O3 (3% AgNO3) using the conventional melt quenching technique. The subsequent thermal treatment of the silver-doped glass fibers, in the range of 150 to 350 °C, for annealing times up to 30 min under reducing hydrogen atmosphere, induces migration of the as-dispersed silver ions toward the surface, where they are reduced to form silver-based shell nanostructures on the glass core. We found the SERS activity of the as-produced glass–silver@core–shell fibers can be easily controlled by setting both the annealing temperature and time. Field-emission scanning electron microscopy (FE-SEM) was used to characterize the morphology of the as-produced SERS active substrates, which were correlated with the SERS signal using cresyl violet (CV) as the model. The as-produced glass substrates decorated with silver-based nanostructures revealed to be a robust candidate and a very efficient SERS substrate, providing Raman signal enhancement of about 105 fold orders of magnitude while compared with the silver-undoped glass substrate. Finally, based on the morphological and optical data we proposed a one-step mechanism for the growth of the silver-based nanostructures under the employed synthesis condition.

Direct laser writing of efficient effective second order nonlinear optical properties in a tailored silver-doped phosphate glass

This last decade, femtosecond (fs) direct laser writing (DLW) has proposed an exponentially growing number of achievements thanks to the simultaneous improvements in both fs laser technologies and material sciences, leading to innovative light/matter interactions [1]. DLW has led to micro and nano-photonics demonstrations of mechanical, chemical and optical contrast in the bulk or at the surface, as differential etching solubility, new linear absorption and fluorescence or plasmonic properties, as well as dielectric phase transition [2]. Nonlinear optical contrast can also appear from third-order nonlinear response enhancement due to density contrast, as proposed for perennial high density data storage [3, 4]. DLW also showed second-order nonlinear optical properties, even in a glassy environment, either due to the localized crystallization of non-centrosymmetric nanocrystalittes [5] or to the production of a buried static space charge separation at the root of the electric field induced second harmonic generation (EFISHG) [6].

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.

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.

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.

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.

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.