Nano-composite soda lime silicate glass prepared using silver ion exchange

Commercial soda lime silicate glasses have been subjected to ion exchange at different temperatures ranging from 320 to 500 °C in a molten mixture of AgNO₃ and NaNO₃ with molar ratio of 10:90, 02:98 and 50:50 for different time periods ranging from 40 to 180 min. Optical and structural properties of the ion exchanged glass are measured using UV–Vis–NIR absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and transmission electron microscopy (TEM). Signature of silver nanoparticle formation is obtained from the UV–Vis–NIR spectra, which shows a peak at 425 nm due to surface plasmon resonance (SPR). Replacement of Na⁺ ions by Ag⁺ ions is inferred from FTIR spectra. Fluorescence spectra reveal the formation of Ag⁰ atoms from Ag⁺ ions at higher temperatures. TEM image shows the silver nanoparticles of average size 3.75 nm. At exchange temperature of 500 °C Ag nanoparticles are formed without post-exchange annealing treatment.     

Up-conversion enhancement in Er3 +-Ag co-doped zinc tellurite glass: Effect of heat treatment

The melt quenching method was used to synthesize the Ag⁰ nanoparticles and Er^3 + ions co-doped zinc tellurite glass. The glasses were characterized by differential thermal analyzer, UV–VIS-IR absorption, photoluminescence spectroscopy and TEM imaging. Heat treatment at different annealing time intervals above the glass transition temperature was applied to reduce the Ag⁺ ions to Ag⁰ NPs. The influence of heat treatment on structural and optical properties is examined. Intense and broad up-conversion emissions of silver are recorded in the visible region. Up-conversion luminescence spectra revealed three major emission peaks at 520, 550 and 650 nm originating from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 levels, respectively. An efficient enhancement in visible region is observed for samples containing silver NPs. The absorption plasmon peaks are evidenced around 560 and 594 nm. The effect of localized surface plasmon resonance and the energy transfer from the surface of silver NP to trivalent erbium ions are described as the sources of enhancement.     

Preparation of core–shell nanospheres of silica–silver: SiO2@Ag

We prepared SiO₂@Ag core–shell nanospheres: silver nanoparticles (～4 ± 2 nm in diameter) coated silica nanospheres (～50 ± 10 nm in diameter). The preparation route is a modification of the Stöber method, and involves the preparation of homogeneous silica spheres at room temperature, combined with the deposition of silver nanoparticles from Ag⁺ in solution, by using water/ethanol mixtures, tetraethyl-orthosilicate as Si source and silver nitrate as Ag source in a single-pot wet chemical route without an added coupling agent or surface modification, which leads to the formation of core@shell homogeneous nanospheres. We present the preparation and characterization of the SiO₂@Ag core–shell nanospheres and also of bare silica spheres in the absence of silver, and propose a reaction mechanism for the formation of the core–shell structure.     

Formation of nanoclusters through silver reduction in glasses: The model

The system of equations describing the formation of silver nanoclusters through the reduction of ionic silver in the course of thermal processing of silver containing glasses in hydrogen is formulated and solved numerically. The processes of the clusterization of neutral silver within the glass and at the surface, and the growth of the nanoclusters are modeled with the account of different mobilities and concentrations of the participating species. The influence of the variation of diffusion coefficients of Ag⁰ atoms, Ag⁺ and H⁺ ions as well as concentration of Ag⁺ ions in the glass matrix. It is shown that concentration distribution of neutral hydrogen (H⁰) strongly depends on the relationship between concentration of Ag⁺ ions (C_Ag⁺) and concentration of neutral hydrogen at the glass surface (C₁), as well as between diffusion coefficients of silver and hydrogen ions. When D_Ag⁺ ≪ D_H⁺ and C_Ag⁺ ≫ C₁, the total hydrogen concentration profile (C_Htot = C_H⁰ + C_H⁺) is defined by silver ion diffusion coefficient D_Ag⁺. Concentration of neutral silver, C_Ag⁰, represents a bell-shaped depth distribution, whose maximum moves to the depth linearly with t^1/2 with the rate depending both on the diffusion coefficient of neutral silver, D_Ag⁰, and neutral hydrogen, D_H⁰. It is shown that the depth position of the maximum coincides with the frontier of the layer filled by clusters. The kinetics of the cluster radius growth in the bulk of the glass also depends both on D_Ag⁰ and D_H⁰ and essentially deviated from the kinetic law R² ∼ t predicted earlier in the assumption of time-independent oversaturation. The kinetics of Ag cluster growth on the glass surface turned out independent of the D_Ag0 diffusion coefficient.     

Efficient plasmonic coupling between Er3 +:(Ag/Au) in tellurite glasses

We report a systematic study of the localized surface plasmon resonance effects on the photoluminescence of Er^3 +-doped tellurite glasses containing Silver or Gold nanoparticles. The Silver and Gold nanoparticles are obtained by means of reduction of Ag ions (Ag⁺ → Ag⁰) or Au ions (Au^3 + → Au⁰) during the melting process followed by the formation of nanoparticles by heat treatment of the glasses. Absorption and photoluminescence spectra reveal particular features of the interaction between the metallic nanoparticles and Er^3 + ions. The photoluminescence enhancement observed is due to dipole coupling of Silver nanoparticles with the ⁴I_13/2 → ⁴I_15/2 Er^3 + transition and Gold nanoparticles with the ²H_11/2 → ⁴I_13/2 (805 nm) and ⁴S_3/2 → ⁴I_13/2 (840 nm) Er^3 + transitions. Such process is achieved via an efficient coupling yielding an energy transfer from the nanoparticles to the Er^3 + ions, which is confirmed from the theoretical spectra calculated through the decay rate.     

Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se₈₀Te₂₀)_100 ? xAg_x (0 ≤ x ≤ 4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328 K) and in between glass transition temperature and crystallization temperature (343 K). Thin films annealed at 343 K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100 nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10^? 5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358 K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.     

Lead sulfide quantum dots in glasses controlled by silver diffusion

Precipitation of PbS quantum dots (QDs) in silicate glasses controlled by Ag⁺ ion diffusion was investigated. Ag⁺ ions penetrated ~ 0.5 μm into the glass when the glass was immersed in the AgNO₃ solution at 80 °C. Ag nano-particles (NPs) and PbS QDs were formed after heat-treatment at temperatures of 420–460 °C for 10 h. PbS QDs in Ag⁺-diffused regions photoluminesced at longer wavelengths than did those in Ag⁺-free regions. This indicates that PbS QDs thus formed in regions containing Ag NPs were larger than those in Ag⁺-free regions and this size difference was confirmed from the transmission electron microscope images. PbS QDs can grow at temperature as low as 420 °C in Ag⁺-diffused regions and this implies that PbS QDs form preferentially using Ag NPs as nucleating agents.     

Surface enhanced Raman scattering in an amorphous matrix for Raman amplification

In order to improve the efficiency of Raman Amplifiers, the Surface Enhanced Raman Scattering (SERS) effect of an amorphous matrix of TiO₂ was studied. First, optimisation of the amorphous layer quality was performed by depositing thin films on glass substrates at different temperatures. Then, thin films of amorphous TiO₂ were deposited on silicon commercial gold SERS substrates (Klarite®) by a dip-coating process. The SERS effect was demonstrated by the great difference of Raman intensities of the amorphous TiO₂ matrix dip-coated on active and inactive parts of Klarite® substrate under 633 nm and 780 nm laser excitations in the tail of the Surface Plasmon Resonance band of gold nanoparticles.     

Microstructural and photocatalytic properties of sol–gel-derived vanadium-doped mesoporous titanium dioxide nanoparticles

The vanadium (V)-doped mesoporous titanium dioxide (TiO₂) nanoparticles at low V/Ti ratios ranging from 0 to 2 wt% were prepared using hydrolytic sol–gel method in the presence of tri-block copolymer Pluronic F127. The microstructures of TiO₂ in terms of morphology, crystallization, chemical states of species, surface area, and band gap were characterized by SEM, TEM, XRPD, XPS, surface area analyzer, and UV–Vis spectrophotometer, respectively. SEM images showed that the V-doped TiO₂ nanoparticles were porous structures, and the surface areas and pore sizes ranged from 86 ± 9 to 96 ± 15 m²/g and from 12 ± 4 to 15 ± 2 nm, respectively. The XRPD patterns indicated that V-doped mesoporous TiO₂ after calcination at 500 °C was mainly anatase phase, and the crystallite sizes were in the range 14–16 nm, which are consistent with the results obtained from SEM images. XPS spectra and HRTEM images showed that vanadia was doped both on the surface and in the lattice of anatase TiO₂. A slight red-shift in wavelength absorption was observed when V/Ti ratio increased from 0 to 2 wt%. Methylene blue (MB) was further used as the target compound to examine the photocatalytic activity of V-doped mesoporous TiO₂ nanocatalysts under illumination of solar simulator or UV light. Addition of vanadium ions slightly decreased the photocatalytic activity of TiO₂ toward the decolorization of MB under the illumination of UV light at 305 nm. However, a 1.6–1.8 times increase in rate constants for MB photodegradation was observed when 0.5–1.0 wt% V-doped TiO₂ was illuminated with sunlight at AM 1.5.     

Influence of Ag nanoparticles on luminescent performance of SiO2:Tb3 + nanomaterials

Tb^3 + single-doped SiO₂ (SiO₂:Tb^3 +) and Tb^3 +, Ag co-doped SiO₂ (SiO₂:Tb^3 +–Ag) nanostructured luminescent materials were prepared by a modified Stöber method. Their microstructure and optical property were investigated using scanning electron microscopy, ultraviolet visible absorption and photoluminescence spectrophotometry. Results show that the samples are composed of well-dispersed near-spherical particles with a diameter about 50 nm, the highest fluorescence intensity is obtained when the doping concentration of Tb^3 + is 4.86 mol%, the corresponding internal quantum efficiency is 13.6% and the external quantum efficiency is 8.2%. The experimental results indicate that Ag nanoparticles can greatly enhance the light absorption at 226 nm and the light emission at 543 nm of SiO₂:Tb^3 +–Ag, and the fluorescence lifetime reduces with increasing Ag concentration in SiO₂:Tb^3 +–Ag. Additionally, the present results indicate that fluorescence enhancement is attributed to the local field enhancement and the increased radiative decay rates induced by Ag nanoparticles.     

Optically induced crystallization in amorphous Agx(Sb0.33S0.67)100−x films

Amorphous films of Ag_x(Sb_0.33S_0.67)_100−x composition, where x was between 0 and 25 at.% Ag, were prepared by pulsed laser deposition and optically induced silver dissolution into the binary Sb-S chalcogenides deposited by vacuum evaporation techniques. We have studied the effect of silver content in the host materials and Ar⁺ ion laser exposure on the optical properties and structure of the films. Optically induced crystallization was demonstrated in films and the kinetics of the crystallization were studied. This work is anticipated to be applicable to optical memories.     

Optically-induced darkening and crystallization in amorphous Ag–Sb–S films

The amorphous films of Sb₃₃S₆₇ and Ag_x(Sb_0.33S_0.67)_100−x composition, where x was between 0 and 25 at.% Ag, were prepared by different techniques, i.e. by vacuum evaporation, optically-induced silver dissolution into the binary Sb–S chalcogenides deposited by vacuum evaporation or by spin-coating techniques. Ternary Ag–Sb–S amorphous films were also prepared directly by pulsed laser deposition. We have studied effect of silver content in the host materials and Ar⁺ ion laser exposure on optical properties and structure of the films. The optically-induced darkening and crystallization was proved in studied films and their potential application in optical memories could be expected.     

Room temperature PbS nanoparticle growth,incubation in porous TiO2 electrode for photosensitization application

We have reported the synthesis of PbS nanoparticles using a layer-by-layer ionic adsorption and reaction method at room temperature. The structural, morphological, optical, electrical and wettability properties were characterized. PbS nanoparticles were found to be oriented along the (2 0 0) plane. These PbS nanoparticles were incubated in porous spin coated TiO₂ films of ∼1 μm thickness using the SILAR method. A change in surface wettability in terms of surface water contact angle measurement was not observed. This confirms the insertion of PbS nanopartcles into porous TiO₂. Finally, photosensitization of the PbS incubated in porous TiO₂ electrode in sodium sulfide electrolyte (80 mW/cm² light intensity) was studied.     

Er3+-doped germanate glasses for active waveguides prepared by Ag+/K+ ↔ Na+ ion-exchange

Planar waveguides were prepared by Ag⁺/K⁺ ? Na⁺ ion-exchange on Er⁺³-doped GeO₂–ZnO–Na₂O–Li₂O glasses obtained by a melting–casting method. Optical parameters of the waveguides were measured at 543.5, 632.8, and 1550 nm by m-line technique as a function of the Ag⁺ ion-exchange time. The optimized planar waveguides show an effective diffusion depth (d) of 2.95 μm and well confined propagating TE₀ and TM₀ modes at 1550 nm. Spectroscopic properties as photoluminescence emission and emission decay time were evaluated for the erbium-doped planar waveguide, indicating that Ag⁺ ? Na⁺ ion-exchange enhance the photoluminescence emissions in the green and infrared regions from erbium ions. The glass system studied is promising to be applied as optical amplifiers in the C-telecom band. Green emission sensitized by Ag⁺ was also observed.     

Ag-doped antibacterial porous materials with slow release of silver ions

The inorganic–organic hybrids of polyethyleneglycol (PEG), tetraethoxysilane (TEOS) and triethylphosphate (TEP) doped by silver ions were prepared by sol–gel method. After molding and heating at 600 °C to remove organic components, porous Ag–P₂O₅–SiO₂ monoliths were obtained. Thermogravimetry (TG), differential thermal analysis (DTA), infrared spectra, ultraviolet–visible (UV–vis) spectra and pore structure of the samples were measured to show that organic components and residual water could be removed by a heat-treatment up to 600 °C and the mesopores with 6 nm pore diameter were formed. Specific surface area and pore volume of the samples were adjusted with different contents of TEP in the starting composition. Ag⁺ ions could be stably released into water at 30 °C up to 28 days. Antibacterial experiment showed that such materials treated at 600 °C could restrain Escherichia coli effectively.     

Compositional dependence of optical parameters in Se–Bi–Te–Ag thin films

Compositional dependence of optical parameters in thermally evaporated amorphous Se_80.5Bi_1.5Te_18 ? yAg_y (for y = 0, 1.0, 1.5 and 2.0 at.%) quaternary thin films has been studied using well established Swanepoel method. The optical properties like, refractive index (n), extinction coefficient (k), absorption coefficient (α) and optical band gap (E_g) have been determined from the transmission spectra in the spectral range from 500 to 2500 nm. The optical band gap (E_g) has been estimated by using Tauc's extrapolation method and is found to increase with an increase in the Ag concentration. Present study shows that the refractive index, extinction coefficient and optical band gap increase with the increasing Ag content which is in agreement with the earlier studies. While the increase in the refractive index with Ag content over the entire spectral range can be attributed to the increased polarizability of larger Ag atomic radius (153 pm) compared to the Te atomic radius (135 pm), the increase in the optical band gap with increasing Ag concentration is correlated to an increase in the cohesive energy and decrease in the electronegativity of the films under study. The dielectric constant and optical conductivity (σ) of the thin films under study are also found to increase with the Ag concentration.     

Hydrothermal synthesis of BaTiO3 thin films on nanoporous TiO2 covered Ti substrates

It is well known that there is an upper limit (<0.25 μm) for the thickness of hydrothermal thin films grown on Ti substrate in the 100–200 °C temperature range, even the reaction time is extended to several weeks. In this paper, BaTiO₃ thin films have been firstly hydrothermally synthesized on titanium substrates covered with a nanoporous TiO₂ layer. By using TiO₂ covered substrates, the thickness of BaTiO₃ films can easily reach ∼1.0 μm at 110 °C after only 2 h hydrothermal treatment. It is found that the large quantity of pores with size at the tens of nanometer range in the oxide layer served as easy paths for the diffusion of Ba²⁺ and OH⁻ and enabled the film grow thicker. SEM and XRD results show that the films are crack-free and in polycrystalline phase.     

FTIR and UV–VIS optical absorption spectra of gamma-irradiated MoO3-doped lead borate glasses

Structure and optical properties of MoO₃-doped lead borate glasses which contain high PbO content (60, 70 and 80%) have been studied using Fourier transform infrared (FTIR) and ultraviolet–visible (UV–VIS) spectroscopic tools. FTIR spectra reveal absorption bands which are characteristic for various structural units of borate network, mainly BO₃ triangles and BO₄ tetrahedra, in addition to the PbO_n (where n = 3 and/or 4) structural units. UV–VIS optical absorption spectra reveal broad intense charge transfer UV bands due to Pb^2 + ions in the range 320–385 nm. Within this range, molybdenum ions, preferably Mo^3 + and Mo^5 +, can interfere at about 360–385 nm. Additionally, molybdenum ions give a weak visible band at about 850–860 nm. The optical absorption spectra of the studied glasses show marked resistance to successive gamma irradiation up to 5 Mrad. This shielding behavior can be related to the present high content of the high atomic mass Pb^2 + ions. Changes in the atomic structure before and after gamma irradiation are described and explained.     

Effect of high electronic energy loss of 100 MeV gold heavy ions in copper chalcogenides (CuX,X = S,Se) at nanoscale: Opto-electronic properties study

The copper chalcogenide (CuX, X = S, Se) thin films have been irradiated with 100 MeV gold swift heavy ions (SHI) at 10¹¹ and 10¹² ions/cm² fluences. The irradiation effects were probed by characterizing physical properties such as XRD, AFM, optical band gap and electrical resistivity of copper chalcogenide thin films. The increase in irradiation fluence increases the particle size, electrical conductivity and PL intensity of the materials, and the optical band edges were red shifted. The results are explained by quantifying electronic energy loss of ions in both the materials.     

Synthesis of two-dimensional metallic silver using sodium beta-alumina crystal channels

Sodium beta-alumina (β-NaAl₁₁0₁₇) crystals were grown within a gel containing Na₂O and Al₂O₃. The glass–crystal composite was put through a Na⁺ ? Ag⁺ ion-exchange reaction. The ion-exchanged glass–crystal was then subjected to an electrodeposition process. Nanosheets of metallic silver were found to have grown within the β-NaAl₁₁0₁₇ channels which usually contain the mobile sodium ions. The DC electrical resistance of the composites was caused due to charge transport in the two-dimensional crystal planes. The average silver layer thickness was ～0.6 nm and the interlayer separation ～1.13 nm.