Spectroscopy of silver complexes in solutions of inorganic compounds

The absorption, photoluminescence, and photoexcitation spectra of a number of inorganic solid solutions with a silver ion impurity have been examined. The influence of the temperature on the spectral characteristics of haloid and oxygen-containing solutions activated with Ag⁺ ions has been investigated. The temperature dependences of the luminescence quantum yield of solid solutions with Ag⁺ impurity in the temperature range 77-150 K have been studied. It is shown that the spectra under observation are conditioned by electron transition between energetic levels of Ag⁺ ion which are deformed because of the interaction with environment.     

EPR and optical spectra of Ni2+-VAg in silver chloride and silver bromide

The optical absorption and EPR spectra of Ni²⁺-V_Ag centres in the AgCl:Ni²⁺ and AgBr:Ni²⁺ systems have been investigated theoretically on the basis of the complete energy matrices including the electron–electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (V_Ag) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to V_Ag is shorter than others for both AgCl:Ni²⁺ and AgBr:Ni²⁺ systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX₆)^4? clusters in AgCl and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni²⁺ ion has a smaller ionic radius and more effective charge than the Ag⁺ ion.     

Photoinduced dissociation reactions of silver fluoride cluster ions

Photoinduced dissociation in the ultraviolet region has been investigated for Ag _nF _n-1 ⁺ cluster ions. Photodissociation spectrum of Ag₂F⁺ in the energy of 3.8–5.6 eV exhibits several sharp bands corresponding to the transition to electronically excited states. In this dissociation, only the Ag₂ ⁺ ion was observed as a fragment ion. Theoretical calculation indicates that the parent Ag₂F⁺ ion has a linear Ag-F-Ag equilibrium geometries in the ground and excited states. Since conformational changes by excitation of bending vibration are necessary for the fragmentation of an F atom, this indicates that production of Ag₂ ⁺ from Ag₂F⁺ is a result of internal conversion and following conformational changes.     

Antimicrobial silver nanoparticles generated on cellulose nanocrystals

We describe a new approach to the formation of silver nanoparticles (Ag NPs) using cellulose nanocrystals. The process involves periodate oxidation of cellulose nanocrystals, generating aldehyde functions which, in turn, are used to reduce Ag⁺ into Ag⁰ in mild alkaline conditions. The nanoparticles were characterized using transmission electron microscopy (TEM) and ultraviolet–visible absorption spectroscopy. From the microscope studies (TEM) we observed that Ag NPs have spherical shape with a size distribution comprise between 20 and 45 nm. The antibacterial activity was assessed using the minimum inhibitory concentration. The antibacterial assays compare favourably with most of other experiments conducted with the same species.     

Metastable fragmentation of silver bromide clusters

The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most abundant species are Ag_nBr_{n - 1} ⁺ and Ag_nBr_{n + 1} ^- and Ag₁₄Br₁₃ ⁺ is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide ionic clusters. From a certain size, Ag_nBr_{n - 1} ⁺ is no more the main series, and Ag_nBr _{n - 2, 3} ⁺ series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental method. The large majority of the cations release mainly a neutral Ag₃Br₃ cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag⁺-Ag⁺ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)₃ and to quasi-planar cyclic structures of (AgBr)_n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)_n, and to cuprous halide compounds. Received 9 November 2000 and Received in final form 25 January 2001     

Dissociation channels of silver bromide cluster Ag<Subscript>2</Subscript>Br,silver cluster Ag<Subscript>3</Subscript> and their ions studied by using alkali metal target

Various dissociation channels of silver bromide cluster ion Ag₂Br⁺ and silver cluster ion Ag₃ ⁺ were observed in high-energy collisionally-activated dissociation (CAD) using a Cs target. The fragment patterns of the high-energy CAD were compared with those of the metastable dissociation and low-energy CAD. The difference in the fragment patterns between the high-energy CAD and the other dissociation methods was explained in terms of the internal energy distributions. The dissociation mechanisms of neutral silver bromide cluster Ag₂Br and silver cluster Ag₃ were also investigated by charge inversion mass spectrometry using the Cs target. While the fragment ions AgBr^- and Ag₂ ^- were dominantly observed in the charge inversion spectrum of Ag₂Br⁺, the undissociated ion Ag₃ ^- was observed as a predominant peak in the case of Ag₃ ⁺. The dissociation behavior of Ag₂Br^* can be explained on the basis of the calculated thermochemical data. Contrary to this, the predominant existence of the undissociated Ag₃ ^- cannot be explained by the reported thermochemical data. The existence of undissociated Ag₃ ^- suggests that the dissociation barrier is higher than the internal energy of Ag₃ ^* (theoretical: 1.03 eV, experimental: 2.31 eV) estimated from the ionization potentials of Ag₃ and Cs.     

Use of a silver ion selective electrode to assess mechanisms responsible for biological effects of silver nanoparticles

For a detailed analysis of the biological effects of silver nanoparticles, discrimination between effects related to the nano-scale size of the particles and effects of released silver ions is required. Silver ions are either present in the initial particle dispersion or released by the nanoparticles over time. The aim of this study is to monitor the free silver ion activity {Ag⁺} in the presence of silver nanoparticles using a silver ion selective electrode. Therefore, silver in the form of silver nanoparticles, 4.2 ± 1.4 nm and 2–30 nm in size, or silver nitrate was added to cell culture media in the absence or presence of A549 cells as a model for human type II alveolar epithelial cells. The free silver ion activity measured after the addition of silver nanoparticles was determined by the initial ionic silver content. The p {Ag⁺} values indicated that the cell culture media decrease the free silver ion activity due to binding of silver ions by constituents of the media. In the presence of A549 cells, the free silver ion activity was further reduced. The morphology of A549 cells, cultivated in DME medium containing 9.1% (v/v) FBS, was affected by adding AgNO₃ at concentrations of ≥30 μM after 24 h. In comparison, silver nanoparticles up to a concentration of 200 μM Ag did not affect cellular morphology. Our experiments indicate that the effect of silver nanoparticles is mainly mediated by silver ions. An effect of silver on cellular morphology was observed at p {Ag⁺} ≤ 9.2.     

Collision induced dissociation of doubly charged silver clusters Agn 2+, n=21,22,23

Doubly charged silver clusters Ag_n ²⁺, n=21, 22, 23, are produced by electron bombardment of an Ag_n ⁺ ensemble stored in a Penning trap. After mass selection the clusters are subjected to collision induced dissociation. The fragmentation channels are determined by time-of-flight mass spectrometry after ejection of the resulting ion ensemble from the trap. Monomer evaporation is the only decay path observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interaction of gold and silver cluster cations with CH<Subscript>3</Subscript>Br: thermal and photoinduced reaction pathways

The reactions of free, size selected Au _n ⁺ (n = 1–3, 5, 7) and Ag₃ ⁺ clusters with CH₃Br as well as the photodissociation of the resulting complexes at 266 nm were studied in a radio frequency ion trap under multiple collision conditions. CH₃Br was found to interact more strongly with the gold clusters than with the silver clusters. All investigated metal clusters exhibited characteristic size dependent adsorbate coverages. Furthermore, the successive loss of methyl radicals was identified as a major thermal reaction channel of the adsorbed CH₃Br molecules. Photodissociation experiments were performed with the product complexes of the trimer clusters and revealed the strongly preferred light-induced fragmentation of Au₃Br₃ ⁺ and Ag₃Br₃ ⁺, respectively, over any other thermal reaction products. However, whereas in the case of the gold cluster complexes the bare Au₃ ⁺ was exclusively re-formed through laser irradiation, considerable photoinduced metal cluster fragmentation occurred in the case of Ag₃Br₃ ⁺.     

Biasing effects on thallium and silver chlorides with dc/ac voltage

Comparison was made between crystals of thallium chloride and silver chloride on their biasing effects with dc/ac voltage. Previous reports say that, although their electrical conductivities are similar, the dominant charge carriers in the former are the Cl⁻ ions while the Ag⁺ ions in the latter. The present dc/ac study demonstrates the following: for thallium chloride, although Cl⁻ conduction may be dominant under low bias field, Tl⁺ conduction supercedes Cl⁻ conduction when the bias field is enhanced. For silver chloride, Ag⁺ conduction is overwhelming within wide temperature range, to cause easy dielectric breakdown on dc biasing. Concerning the extrinsic conductivity seen at temperatures below 60 °C (thallium chloride) or below 150 °C (silver chloride), it is ascribed to grain-boundary related electron conduction, not to grain-boundary related Tl⁺ or Ag⁺ conduction as reported earlier.     

Improved modification of clinoptilolite with silver using ultrasonic radiation

The modification of natural clinoptilolite with silver ions using ultrasound has been investigated in the current work. The modification process was performed using clinoptilolite of different fractions (0–3.0 mm) over the temperature range of 25–55 °C, ultrasonic power range of 8.0–12.5 W and AgNO₃ concentration range of 0.01–0.1 M. The zeolite modification was performed in the presence of sonication and mechanical stirring in separate runs for comparison. Fundamental analysis demonstrated that the use of ultrasound ensures desorption of air from clinoptilolite particles and accelerates the diffusion of Ag⁺ ions and subsequent ion exchange. Increasing the particle size of clinoptilolite led to a natural decrease in its sorption capacity. A slight increase in the sorption capacity with an increase in the equivalent particle diameter from 0.081 to 0.35 mm was seen due to changes in the structure of clinoptilolite particles during mechanical grinding. The calculated temperature coefficient of the sorption process of Ag⁺ ions as <1.47 means that the modification takes place with dominant control in the intradiffusion region. Increasing the power of ultrasonic irradiation did not provide a monotonous change in the sorption capacity of clinoptilolite. Increasing the concentration of argentum nitrate solution provided an increase in the content of silver ions in clinoptilolite. In general, the advantage of using ultrasonic vibrations to modify the natural clinoptilolite of different fractions with Ag⁺ ions was demonstrated in terms of achieving higher sorption capacity, also elucidating the effect of different operating conditions.     

On the possibility of a forecast for off-centre configuration of Ag+ and Cu+ in alkali halide crystals

Summary The simple cut criterion based on the accurate determination of the radii of the ions in alkali halides and previously introduced by the authors for forecasting off-centre configuration of Li⁺ and F⁻ has been extended to heavy ions (Ag⁺ and Cu⁺). It has been found that this criterion is valid for the Ag⁺ ion, whereas for Cu⁺ gives a less precise forecast because of the lack in knowledge of the effective partial charge on Cu⁺ ion. It has been evidenced that the critical value of the ratior ₊ ^* /r ₊ between impurity and host ion radius which allows off-centre configuration is dependent on the impurity ion mass. Work jointly supported by the Ministero della Pubblica Istruzione and by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Struttura della Materia.     

Hole-electron mechanism of F-H pair generation in RbCl crystals with impurity electron traps

Production of F, Cl ₃ ⁻ , Ag⁰, and Tl⁰ centers in RbCl:Ag and RbCl:Tl crystals by photons having energies ranging from 5 to 10 eV has been studied at 295 and 180 K. It is shown that creation of near-impurity excitations is accompanied by formation of F centers localized in the vicinity of Ag⁺ and Tl⁺ ions. F centers are produced in direct optical generation of self-trapped excitons. In addition to the well-known mechanism of F-H pair production in nonradiative recombination of electrons with self-trapped holes, a hole-electron process has been revealed for the first time to operate in RbCl:Ag having deep electron traps. By this mechanism, F-H pairs appear in the following sequence of stages: thermally stimulated unfreezing of hopping diffusion of self-trapped holes (V _K centers), tunneling electron transfer from Ag⁰ to the approaching V _K centers, and subsequent nonradiative decay of triplet self-trapped excitons near Ag⁺ ions. Fiz. Tverd. Tela (St. Petersburg) 40, 1238–1245 (July 1998)     

Ag+掺杂的立方相Y2O3:Eu纳米晶体粉末发光强度研究

采用化学自燃烧法制备了不同Ag⁺掺杂浓度的Y₂O₃:Eu纳米晶体粉末样品(［Y³⁺］∶［Eu³⁺］∶［Ag⁺］=99∶1∶X，X=0—3.5×10^-2)，以及通过退火处理得到了相应的体材料.根据X射线衍射谱确定所得纳米和体材料样品均为纯立方相.实验表明在纳米尺寸样品中随着Ag离子浓度的增加，荧光发射强度随之增加，当X=2×10^-2时达到最大值，其发光强度比X=0时提高了近50%.当Ag离子浓度继续增加，样品发光强度保持不变.在相应的体材料样品中则没有观察到此现象.通过对各样品的发射光谱，激发光谱，X射线衍射图谱，透射电镜(TEM)照片和荧光衰减曲线的研究，分析了引起纳米样品荧光强度变化的原因是由于Ag离子与表面悬键氧结合，从而使这一无辐射通道阻断，使发光中心Eu³⁺的量子效率提高；Ag⁺的引入所带来的另一个效应是使激发更为有效.这两方面原因使发光效率得到了提高.     

Effect of implantation regimes of silver ions on the structure and optical properties of zinc-oxide nanocrystalline films

Thin (about 270 nm) nanocrystalline films of zinc oxide (ZnO) are obtained on quartz substrates using ion sputtering and irradiated with Ag⁺ ions at an energy of 30 keV and relatively high fluences at ion current densities of 4, 8, and 12 µA/cm². The X-ray analysis, scanning electron microscopy, and optical spectroscopy are used to study the effect of irradiation dose and ion current density on the structural modification and optical properties of the ZnO films. Nontrivial dependences of the structural and optical parameters of the films on the ion irradiation regimes are due to radiation heating and film sputtering under the action of the ion beam, diffusion of impurity, formation of silver nanoparticles in the irradiated layer at high implantation fluences, and the diffusion of implanted impurity at relatively high ion current densities.     

Immobilization of silver nanoparticles on silica microspheres

The silver nanoparticles (Ag NPs) have been immobilized onto silica microspheres through the adsorption and subsequent reduction of Ag⁺ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared through sol–gel processing; their surfaces were then functionalized using 3-mercaptopropyltrimethoxysilane (MPTMS). The major aims of this study were to immobilize differently sized Ag particles onto the silica microspheres and to understand the mechanism of formation of the Ag nano-coatings through the self-assembly/adsorption behavior of Ag NPs/Ag⁺ ions on the silica spheres. The obtained Ag NP/silica microsphere conglomerates were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Their electromagnetic wave shielding effectiveness were also tested and studied. The average particle size of the obtained Ag NPs on the silica microsphere was found that could be controllable (from 2.9 to 51.5 nm) by adjusting the ratio of MPTMS/TEOS and the amount of AgNO₃.     

Vibrational wave packet dynamics in the silver tetramer probed by NeNePo femtosecond pump-probe spectroscopy

We present results on the ultrafast dynamics of mass-selected neutral Ag₄ clusters using NeNePo (negative ion - neutral - positive ion) femtosecond pump-probe spectroscopy. One-color pump-probe spectra of the Ag₄ ^-/Ag₄/Ag₄ ⁺ system measured at 385 nm and an internal cluster temperature of 20 K display a complex beat structure over more than 60 ps. The oscillatory structure is attributed to vibrational wave packet dynamics in an excited “dark" state of neutral Ag₄. A dominant 740 fs wave packet period as well as wave packet dephasing and rephasing are observed in the spectra. Fourier analysis of the spectra yields a group of frequencies centered around 45 cm^-1 and an anharmonicity χ _e2νχ _eχ _e of 2.65 cm^-1 for the active vibrational mode. Received 30 November 2000     

Investigations on field desorption products from silver surfaces by mass spectrometry

Field evaporation of silver and field desorption of silver surface compounds were investigated by analysing positive ions with a mass spectrometer. In particular, the well known adsorption states of oxygen, and further the interactions of H₂O, NH₃, H₂, CO and CH₄ were measured in the field ion mass spectrometer under steady state fields of > 0.1 V/Å with a sensitivity of < 0.1 ions s^?1 and at temperatures between 80 °K and 425 °K. Although oxygen is usually chemisorbed at Ag surfaces, no AgO⁺, AgO⁺₂ or other Ag-O compounds could be detected as positive ions, Ag⁺ and O₂⁺ are the only observed ions at best image fields in oxygen up to fields of field evaporation of Ag⁺(≈ 2.2 V/Å). Even after the actual adsorption of oxygen with zero-field (6 × 10⁵ Langmuir at 10^?3 Torr) at 323 °K and 473 °K and subsequent application of the desorption field at 210°K no silver-oxygen compounds were found in positive ionic form. Small quantities of AgO⁺ and AgO⁺₂ were only formed — besides Ag(H₂O)_x⁺ complexes — if atomic oxygen was supplied by the field induced dissociation of water.Gases which do not adsorb on silver under zero-field conditions (H₂, CO, CH₄, N₂) yield the ions Ag(H₂)_n, Ag(CO)_n⁺, n=1, 2; AgCH₄⁺, AgN₂⁺. The situation with H₂O and NH₃ is more complicated: Molecular ions [Ag(H₂O)_n]⁺·mH₂O, n=1,…, 4, m=1,…, 8 and [Ag(NH₃)_n]⁺·mNH₃, n=1, 2, m=1,…, 6 are found besides Ag⁺.From the temperature and field dependence conclusions are drawn about the mechanisms of evaporation and formation of ionic surface complexes. The activation energies of evaporation of Ag⁺ are found to depend on the square root of the field strength. In general, the generation of surface compounds can be described by field induced reactions rather than usual gas adsorption.