Formation of silver nanoparticles in photothermorefractive glasses during electron irradiation

The formation of silver nanoparticles in photothermorefractive glasses during electron irradiation and subsequent heat treatment is experimentally studied. The optical density spectra of samples at various stages of heat treatment are compared. The formation of metallic nanoparticles is shown to occur during both electron irradiation and subsequent heat treatment. Nanoparticles are localized in layers parallel to the surface. At the initial stage of nanoparticle formation, the key role is played by the appearance of a negative bulk charge in the near-surface layer in glass, which results in the field-assisted migration of positive metal ions and a characteristic layered distribution of metallic nanoparticles in the glass volume.     

Influence of UV irradiation and heat treatment on the luminescence of molecular silver clusters in photo-thermo-refractive glasses

The luminescence spectra of photo-thermo-refractive (PTR) glasses containing cerium, silver, and antimony ions before and after UV irradiation and after heat treatment have been thoroughly investigated for the first time. It is shown that silver is present in the initial PTR glass in the form of ions and positively charged molecular clusters. After UV irradiation into the absorption band of cerium ions, silver partially passes to the neutral state in the form of atoms and neutral molecular clusters Ag₂, Ag₃, and Ag₄, which exhibit bright luminescence in the visible spectral range. Subsequent heat treatment at a temperature below the glassformation temperature leads to an increase in the luminescence intensity due to the increase in the concentration of neutral molecular clusters. Heat treatment at a temperature above the glass-formation temperature leads to the formation of silver nanocrystals and luminescence quenching. It is proposed to use PTR glasses with molecular silver clusters as phosphors for converting UV radiation into the visible range for solar power engineering and white LEDs.     

Preparation of silver nanoparticles by laser ablation in polyvinylpyrrolidone solutions

We performed laser ablation of a silver plate in polyvinylpyrrolidone (PVP) aqueous solutions to prepare silver nanoparticles. Secondary laser irradiation onto the prepared colloidal solutions was also carried out. It was revealed that the formation efficiency was increased by addition of PVP as well as the stability of nanoparticles. The result of shadowgraph measurements suggested that the increased ablation efficiency by PVP is attributable to increased secondary etching efficiency by the solvent-confined plasma toward the silver plate. On the other hand, the size decrease of the nanoparticles by addition of PVP was more remarkable during the secondary irradiation process than in the laser ablation (nanoparticle preparation) process. This result indicates that emitted materials interact less sufficiently with PVP molecules in the laser ablation process than in the secondary laser irradiation process.     

Formation of silver nanoparticles with dielectric shell on the silver-containing glass during laser evaporation and ablation

We demonstrate a new method of silver nanoparticles formation on a silver-containing glass surface due to its irradiation by a pulsed CO₂ and YAG:Nd lasers. The particles are formed as a result of reduction of silver ions from the glass at the edges of a laser torch emerging during evaporation and ablation. The settled particles are then fixed on sample surface by a shell of glass dielectric components. The method allows creating plasmonic nanostructures on the glass surface for sensing applications.     

采用紫外光照法在磷酸盐玻璃中合成CdS/Ag复合微粒

掺杂有Ⅱ-Ⅵ族半导体纳米颗粒(如CdS)或者过渡金属(如Ag)的玻璃由于其较大的非线性光学效应而引起人们的极大兴趣,而同时掺杂有半导体/金属的复合微粒则可以进一步增强玻璃的三阶非线性效应,因此成为目前的研究热点。我们利用玻璃沉淀技术及随后的热处理和紫外光还原技术制备了含高浓度(1%)Ag微粒的玻璃,并采用X射线衍射分析了其物相,用高分辨扫描电镜分析了其形貌,以及测试了其吸收和发光性能。从CdS/Ag复合微粒的扫描照片可以发现晶粒均匀分布在玻璃中,尺寸约为1μm。X射线衍射发现经过热处理和紫外光照的样品衍射峰中含有CdS和Ag,而只进行热处理的样品则只含有CdS,未处理的样品则显非晶态。CdS/Ag复合微粒的吸收峰呈现典型的表面等离子共振峰(420nm)以及CdS的峰(600nm),只含有CdS微粒的样品的吸收峰则在480nm附近,未处理的样品在320nm附近有一个吸收峰,这可能是由于样品在快速冷却过程中的微小晶化造成的。只含有CdS微粒的样品有三个明显的发光峰,然而CdS/Ag复合微粒的发过峰则消失。我们提出了共振能量转移机制来解释该现象。讨论了紫外光照还原Ag微粒的机制。可以认为通过紫外光照,CdS表面的电子被激发出来还原Ag+,从而形成银颗粒,伴随着空穴则被表面缺陷所捕获。     

Cerium oxide nanoparticles protect primary mouse bone marrow stromal cells from apoptosis induced by oxidative stress

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 10⁸ to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.     

The effect of silver on the optical,spectral-luminescent,and crystallization properties of bromide photo-thermo-refractive glasses

The effect of silver on the optical, spectral-luminescent, and crystallization properties of bromide photo-thermo-refractive glasses is studied. Multicomponent photosensitive glasses of the Na₂O–ZnO–Al₂O₃–SiO₂ system with photosensitizing agents (cerium, antimony, silver) and halogenides (fluorine and bromine) are synthesized. Ultraviolet irradiation and thermal treatment below the glass-transition temperature of the glasses cause the formation of silver molecular clusters, which exhibit luminescence in the visible and infrared regions. UV irradiation and thermal treatment of glasses above the glass-transition temperature lead to the growth of silver nanoparticles with plasmon resonance peak in the region of 420 nm. Further thermal treatment of glasses above the glass-transition temperature shifts the plasmon-resonance maximum by 70 nm to longer wavelengths, which is related to the growth of a crystalline shell consisting of mixed silver and sodium bromides on nanoparticles. This formation of a crystalline phase on colloidal centers results in a local increase in the refractive index of the irradiated region by +Δn ~ 900 ppm compared to the nonirradiated region. Photo-thermo-refractive glasses with increased silver concentration are promising photosensitive materials for creating holographic optical elements and devices for line narrowing and stabilizing filters, spectral beam combiners, and filters for increasing the spectral brightness of laser diodes. A positive change in the refractive index of Photo-thermo-refractive glasses provides the possibility of recording in them 3D waveguide and integrated-optical structures.     

Solgel synthesis and structural characterization of silver-silica nanocomposites

The solgel process has been successfully used to prepare silver/silica nanocomposites. After drying in air at 50°C for 30 min, samples were heat treated in air, at 100, 200, 400 and 500°C for the formation of silver nanoparticles. Evolution of silver nano-particles in the amorphous SiO₂ matrix as a function of annealing temperature has been studied. Characterizations were made by X-ray diffraction, ultraviolet-visible, and infrared spectroscopy. Mechanisms of silver clusters formation in the densified silica matrix with respect to thermal treatment are discussed.     

Surface Modification of Silver Iodide Films by Electron Irradiation

It has been found experimentally that electron irradiation of polycrystalline AgI films leads to the formation of a nanocrystalline silver particle monolayer. With an increase in the irradiation time, the nanoparticle size grows but the concentration of the particles first increases and then drops. Formation mechanisms of the nanoparticles and the dynamics of their growth have been considered. Ostwald’s ripening, fieldinduced migration, and nanoparticle charge variation during irradiation by low-energy electrons have been shown to be the main processes responsible for the above effects.     

The Effect of UV Irradiation on the Formation of Silver Molecular Clusters and Their Stabilization in Solutions and Composite and Oxide Coatings

Optics and Spectroscopy - The influence of UV irradiation on the formation of molecular silver clusters in aqueous solutions containing silver, zinc, magnesium nitrates, and polyvinylpyrrolidone...     

Laser sintering of silver nanoparticle thin films: microstructure and optical properties

We present a method for the sintering of silver (Ag) nanoparticle thin films by millisecond pulsed laser irradiation. The microstructure of sintered thin films and sintering behaviors of nanoparticles were systematically investigated in this paper. Absorption spectra of sintered thin films showed blue-shifted surface plasmon resonances (SPR) from 500 nm to 480 nm and red-shifted from 480 nm to 550 nm when laser power was varied from 100 W to 140 W and from 140 W to 200 W, respectively. This indicates a new technique to control light absorption through joining nanoparticles with laser sintering. According to theoretical calculations based on a heat diffusion model, the melting temperature of these Ag nanoparticles was estimated to be 440 °C during laser irradiation.     

Structural Characteristics of Metal Nanoparticles in Glass Upon Irradiation-Assisted Processing

Irradiation-assisted processing, i.e. ion, electron and laser irradiation, have been applied to fabricate metal/glass nanocomposites. The particle configurations are studied by transmission electron microscopy to get some insight into the rather complex formation mechanisms. Special attention is given to spheroidally shaped particles surrounded by smaller secondary particles observed upon ion beam mixing of silica/silver/silica layer compounds as well as irradiating femtosecond laser pulses on sodium silicate glass containing spherical silver particles. Another unique type of structure are cavities observed in silver particles formed by high fluence ion implantation into silica as well as upon laser pulse irradiation of silver particles in glass. The experimental findings are discussed in terms of irradiation-induced defect formation and radiation-enhanced diffusion.     

Erratum to Formation and control of Au and Ag nanoparticles inside borate glasses using femtosecond laser and heat treatment

We report the spectroscopic properties of femtosecond laser-irradiated sodium-alumino-borate glass doped with silver and gold ions. We precipitated gold and silver nanoparticles by laser irradiation and annealing at 400°C for 30 min. The irradiation and annealing treatment produced different absorption and emission characteristics in Au³⁺ doped and Au³⁺, Ag⁺ codoped glasses, and the possible mechanisms of the observed results are discussed. The size of the nanoparticles was estimated by TEM and absorption band analysis.     

Characterization of silver nanomeshes generated by laser-induced photoreduction from a solid silver nitrate thin film

This study characterizes electrical properties of silver thin films with meshed nanostructures fabricated through the photoreduction of solid silver nitrate thin films using excimer laser irradiation. Variations of mesh morphology as functions of laser irradiation time and fluences are examined; and the relationship between the film’s electrical resistance and mesh structure are addressed. The course of nanomesh formation can be separated into two main phases: precipitation of silver nanoparticles as a result of photoreduction; and, formation of mesh nanostructures through the photothermal effect. The resulting electrical resistance depends strongly on the mesh nanostructure. With a suitable arrangement of laser fluence and irradiation time, silver thin films with well interconnected nanomeshes can be fabricated. Results show that silver thin films with low electrical resistivity, down to 8.5×10⁻⁸ Ω m, are easily obtainable. The laser reduction approach takes advantage of the flexibility in local patterning. Moreover, the reduction is from a solid silver nitrate thin film and is executed in the ambient environment that renders this approach a potential method for low-temperature fabrication of metallic electrode conductors for organic electronics.     

Dynamics of formation and decay of supercritical fluid silver colloid under pulse laser ablation conditions

The effect of the density of supercritical carbon dioxide (SC-CO₂) on the dynamics of formation of supercritical fluid (SCF) silver colloids during pulse laser ablation and their post-pulse degradation was studied by in situ UV/vis absorption spectroscopy. Laser irradiation of a silver target in SC-CO₂ caused ablative formation of Ag nanoparticles of different shapes and sizes: quasi-spherical particles (~4 nm) and larger Ag nanoparticles (hundreds of nanometers). A change in the colloid density from 0.24 to 0.82 g/cm³ caused significant changes in the dynamics of ablative formation of large and small particles, the rate of aggregation of small Ag particles into large particles, and the rate of gravitation-induced sedimentation of nanoparticles in the SCF colloid.     

X-ray surface radiolysis: Kinetics of the metal-organic interface formation

Grazing incidence x-ray irradiation of a Langmuir monolayer deposited at the interface between an aqueous silver salt solution and the air leads to the formation of a metallic silver layer of thickness about 4.5 nm, in agreement to the x-ray penetration depth at the air – water interface. Moreover using the scattering and fluorescence induced by the x-ray, we show that it is possible to follow the kinetics of formation of the layer. It appear that the silver layer is formed in two steps: first, the formation of small oriented cristallites, and second, the coalescence of the cristallites forming large plates.     

Simulation of generation of ultradisperse particles upon irradiation of metals by a high-power electron beam

A model of formation of ultradisperse particles in the plasma torch emerging during evaporation of a metal target by a high-power electron beam is described. A model of heterogeneous media is proposed for describing the plasma torch dynamics taking into account heat conduction, heat transfer and friction between components, relaxation of components to equilibrium, condensation, and evaporation and coagulation of drops as a result of their collisions. Numerical simulation of the generation of ultradisperse particles in the plasma torch formed during irradiation of a metal target by a powerful electron beam is performed. The size distribution of ultradisperse particles is obtained for various regimes of irradiation and cooling.     

The influence of low-temperature silver-ion exchange on the spectral-luminescent properties of fluorophosphate glasses doped with PbSe

Changes in the absorption and luminescence spectra of fluorophosphate glasses doped with PbSe caused by low-temperature Ag⁺–Na⁺ ion exchange are considered. It is found that the silver distribution gradient in a near-surface layer about 16 μm thick leads to two different processes of interaction between metal and semiconductor nanoparticles. PbSe molecular clusters and quantum dots more efficiently grow in deep layers with a low silver concentration. The near-surface glass layers with a high silver concentration exhibit formation of Ag metal nanoparticles, on the surface of which interaction with PbSe molecular clusters leads to the formation of Ag–Se–Pb bonds, which transform into Ag₂Se layers in the process of heat treatment. The appearance of the new phase is confirmed by X-ray diffraction.     

Influence of the heat treatment on the nucleation of silver nanoparticles in Tm3+ doped PbO-GeO2 glasses

Nucleation of silver nanoparticles (NPs) in Tm³⁺ doped PbO-GeO₂ (PGO) glass is reported. The influence of the heat treatment on the nucleation of silver NPs is studied by means of transmission electron microscopy and optical spectroscopy. Two heat treatment procedures were applied in order to compare their performance. Observation of infrared-to-visible frequency upconversion (UC) luminescence of Tm³⁺ ions is reported and correlated with the heat-treatment procedure. Enhancement of the UC emission for samples heat treated during various time intervals is attributed to the increased local field in the vicinity of the NPs. Quenching of the UC signal was also observed and correlated with the growth of NPs amount and size.     

Luminescence properties of femtosecond-laser-activated silver oxide nanoparticles embedded in a biopolymer matrix

Strong visible luminescence is observed from silver clusters generated by femtosecond-laser-induced reduction of silver oxide nanoparticles embedded in a polymeric gelatin matrix. Light emission from the femtosecond-laser-activated matrix areas considerably exceeds the luminescence intensity of similarly activated bare silver oxide nanoparticle films. Optical spectroscopy of the activated polymer films supports the assignment of the emissive properties to the formation of small silver clusters under focused femtosecond-laser irradiation. The size of the photogenerated clusters is found to sensitively depend on the laser exposure time, eventually leading to the formation of areas of metallic silver in the biopolymer matrix. In this case, luminescence can still be observed in the periphery of the metallic silver structures, emphasizing the importance of the organic matrix for the stabilization of the luminescent nanocluster structures at the metal–matrix interface. PACS 78.66.Qn; 78.20.-e; 78.40.-q; 78.67.Bf; 78.68.+m