Frequency upconversion luminescence from Yb(+3)-Tm(+3) codoped PbO-GeO(2) glasses containing silver nanoparticles

Infrared-to-visible and infrared-to-infrared frequency upconversion processes in Yb(3+)-Tm(3+) doped PbO-GeO(2) glasses containing silver nanoparticles (NPs) were investigated. The experiments were performed by exciting the samples with a diode laser operating at 980 nm (in resonance with the Yb(3+) transition (2)F(7/2)->(2)F(5/2)) and observing the photoluminescence (PL) in the visible and infrared regions due to energy transfer from Yb(3+) to Tm(3+) ions followed by excited state absorption in the Tm3+ ions. The intensified local field in the vicinity of the metallic NPs contributes for enhancement in the PL intensity at 480 nm (Tm(3+) :(1)G(4)->(3)H(6)) and at 800 nm (Tm(3+) : (3)H(4) -> (3)H(6)). (C) 2009 American Institute of Physics. [doi:10.1063/1.3211300]

Preparation and characterization of the novels terpolymers of poly-{trans-[RuCl(2)(vpy)(4)]-styrene-divinylbenzene} and styrene-divinylbenzene-vinylpiridine impregnated with silver nanoparticles

This paper reports the preparation and characterization of poly-{trans-[RuCl(2)(vpy)(4)]-styrene-divinylbenzene} and styrene-divinylbenzene-vinylpiridine filled with nanosilver. Theses materials were synthesized by non aqueous polymerization through a chemical reaction using benzoyl peroxide as the initiator. The nanosilver was obtained from chemical reduction using NaBH(4) as reducing agent and sodium citrate as stabilizer. The nanometric dimension of nanosilver was monitored by UV-visible and confirmed through TEM. The morphology was characterized by SEM and the thermal properties were done by TGA and DSC. The antimicrobial action of the polymers impregnated with nanosilver was evaluated using both microorganisms, Staphylococcus aureus and Escherichia coli. The antimicrobial activity of the poly-{trans-[RuCl(2)(vpy)(4)]-styrene-divinylbenzene} filled with nanosilver was confirmed by the presence of an inhibition halo of the bacterial growth in seeded culture media, but was not confirmed to the styrene-divinylbenzene-vinylpiridine. The present work suggest that trans - [RuCl(2)(vpy)(4)] complex facilitate the release of silver ion from the media.

Luminescence of Tb(3+) doped TeO(2)-ZnO-Na(2)O-PbO glasses containing silver nanoparticles

Luminescence properties of Tb(3+) doped TeO(2)-ZnO-Na(2)O-PbO glasses containing silver nanoparticles (NPs) were investigated. The absorption band due to the surface plasmon resonance in the NPs was observed. Its amplitude increases with the heat treatment of the samples that controls the nucleation of the NPs. Tb(3+) emission bands centered at approximate to 485, approximate to 550, approximate to 585, and approximate to 623 nm were detected for excitation at 377 nm. The whole spectrum is intensified by the appropriate annealing time of the samples. Enhancement by approximate to 200% of the Tb(3+) luminescence at 550 nm was observed for samples annealed at 270 degrees C during 62 h. This enhancement effect is due to the local field amplitude that increases with the amount of silver NPs and their aggregates. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3010867]

Surface-plasmon-enhanced frequency upconversion in Pr(3+) doped tellurium-oxide glasses containing silver nanoparticles

A frequency upconversion process in Pr(3+) doped TeO(2)-ZnO glasses containing silver nanoparticles is studied under excitation with a nanosecond laser operating at 590 nm, in resonance with the (3)H(4)-->(1)D(2) transition. The excited Pr(3+) ions exchange energy in the presence of the nanoparticles, originating efficient conversion from orange to blue. The enhancement in the intensity of the luminescence at similar to 482 nm, corresponding to the (3)P(0)-->(3)H(4) transition, is due to the influence of the large local field on the Pr(3+) ions, which are located near the metallic nanoparticles. (C) 2008 American Institute of Physics.

Influence of the heat treatment on the nucleation of silver nanoparticles in Tm(3+) doped PbO-GeO(2) glasses

Nucleation of silver nanoparticles (NPs) in Tm(3+) doped PbO-GeO(2) (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 Tm(3+) 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.

Electron beam induced second-harmonic generation in Er(3+) doped PbO-GeO(2) glasses containing silver nanoparticles

Electron beam induced second harmonic generation (SHG) is studied in Er(3+) doped PbO-GeO(2) glasses containing silver nanoparticles with concentrations that are controlled by the heat-treatment of the samples. The SHG is observed at T = 4.2 K using a p-polarized laser beam at 1064 nm. Enhancement of the SHG is observed in the samples that are submitted to electron beam incidence. The highest value of the nonlinear susceptibility, 2.08 pm/V, is achieved for the sample heat-treated during 72 h and submitted to an electron beam current of 15 nA. The samples that were not exposed to the electron beam present a susceptibility of a parts per thousand 0.5 pm/V.

Size effects on silver nanoparticles` properties

In this work a systematic study of the dependence of the structural, electronic, and vibrational properties on nanoparticle size is performed. Based on our total energy calculations we identified three characteristic regimes associated with the nanoparticle`s dimensions: (i) below 1.5 nm (100 atoms) where remarkable molecular aspects are observed; (ii) between 1.5 and 2.0 nm (100 and 300 atoms) where the molecular behavior is influenced by the inner core crystal properties; and (iii) above 2.0 nm (more than 300 atoms) where the crystal properties are preponderant. In all considered regimes the nanoparticle`s surface modulates its properties. This modulation decreases with the increasing of the nanoparticle`s size.

Silver Nanoparticles Obtained in PAH/PAA-Based Multilayers by Photochemical Reaction

Carboxylic acid groups in PAH/PAA-based multilayers bind silver cations by ion exchange with the acid protons. The aggregation and spatial distribution of the nanoparticles proved to be dependent oil the process used to reduce the silver acetate aqueous solution. The reducing method with ambient light formed larger nanoparticles with diameters ranging from 4-50 nm in comparison with the reduction method using UV light, which gave particles with diameters of 2-4 nm The high toughness of samples reduced by ambient light is a result of two population distributions of particle sizes caused by different mechanisms when compared with the UV light process. According to these phenomena, a judicious choice of the spectral source call be used as a way to control the type and size of silver nanoparticles formed on PEMs. Depending on the energy of the light source, the Ag nanoparticles present cubic and/or hexagonal crystallographic structures, as confirmed by XRD. Beyond the kinetically controlled process of UV photoinduced cluster formation, the annealing produced by UV light allowed a second mechanism to modify the growth rates, spatial distribution, and phases.

High performance magnetic separation of gold nanoparticles for catalytic oxidation of alcohols

We present the magnetic separation approach to facilitate the recovery of gold nanoparticle (AuNP) catalysts. The use of magnetically recoverable supports for the immobilization of AuNPs instead of traditional oxides, polymers or carbon based solids guarantees facile, clean, fast and efficient separation of the catalyst at the end of the reaction cycle. Magnetic separation can be considered an environmentally benign separation approach, since it minimizes the use of auxiliary substances and energy for achieving catalyst recovery. The catalyst preparation is based on the immobilization of Au(3+) on the surface of core-shell silica-coated magnetite nanoparticles, followed by metal reduction using two different methods. AuNPs were prepared by thermal reduction in air and by hydrogen reduction at mild temperature. Interestingly, the mean particle size of the supported AuNPs was similar (ca. 5.9 nm), but the polydispersity of the samples is quite different. The catalytic activity of both catalysts in the aerobic oxidation of alcohols was investigated and a distinct selectivity for benzyl alcohol oxidation was observed.

Clean preparation of methyl esters in one-step oxidative esterification of primary alcohols catalyzed by supported gold nanoparticles

Methyl esters were prepared by the clean, one-step catalytic esterification of primary alcohols using molecular oxygen as a green oxidant and a newly developed SiO(2)-supported gold nanoparticle catalyst. The catalyst was highly active and selective in a broad range of pressure and temperature. At 3 atm O(2) and 130 degrees C benzyl alcohol was converted to methyl benzoate with 100% conversion and 100% selectivity in 4 h of reaction. This catalytic process is much ""greener"" than the conventional reaction routes because it avoids the use of stoichiometric environmentally unfriendly oxidants, usually required for alcohol oxidation, and the use of strong acids or excess of reactants or constant removal of products required to shift the equilibrium to the desired esterification product.

Production and characterization of RF-sputtered PbO-GeO(2) amorphous thin films containing silver and gold nanoparticles

In the present work we report the characterization of PbO-GeO(2) films containing silver nanoparticles (NPs). Radio Frequency (RF) co-sputtering was used for deposition of amorphous films on glass substrates. Targets of 60PbO-40GeO(2) (in wt%) and bulk silver with purity of 99.99% were RF-sputtered using 3.5 m Torr of argon. The concentration of silver and gold NPs in the films was controlled varying the RF-power applied to the targets (40-50W for the PbO-GeO(2) target; 6-8 W for the metallic target). The films obtained were annealed in air at different temperatures and various periods of time. Absorption measurements have shown strong NPs surface plasmon bands. Different widths and peak wavelengths were observed, indicating that size, shape and distribution of the silver NPs are dependent on the deposition process parameters and on the annealing of the samples. X-Ray Fluorescence and Transmission Electron Microscopy were also used to characterize the samples. (C) 2010 Elsevier B.V. All rights reserved.

On the Stabilization of Gold Nanoparticles over Silica-Based Magnetic Supports Modified with Organosilanes

The immobilization of gold nanoparticles (Au NPs) on silica is made possible by the functionalization of the silica surfaces with organosilanes. Au NPs could only be stabilized and firmly attached to silica-support surfaces that were previously modified with amino groups. Au NPs could not be stabilized on bare silica surfaces and most of the NPs were then found in the solution. The metal-support interactions before and after the Au NP formation, observed by X-ray absorption fine structure spectroscopy (XAFS), indicate a stronger interaction of gold-(III) ions with amino-modified silica surfaces than with the silanol groups in bare silica. An amino-modified, silica-based, magnetic support was used to prepare an active Au NP catalyst for the chemoselective oxidation of alcohols, a reaction of great interest for the fine chemical industry.

Aerobic oxidation of monoterpenic alcohols catalyzed by ruthenium hydroxide supported on silica-coated magnetic nanoparticles

Ruthenium hydroxide supported on silica-coated magnetic nanoparticles was shown to be an efficient heterogeneous catalyst for the liquid-phase oxidation of a wide range of alcohols using molecular oxygen as a sole oxidant in the absence of co-catalysts or additives. The material was prepared through the loading of the amino modified support with ruthenium(III) ions from an aqueous solution of ruthenium(III) chloride followed by treatment with sodium hydroxide to form ruthenium hydroxide species. Characterizations suggest that ruthenium hydroxide is highly dispersed on the support surface, with no ruthenium containing crystalline phases being detected. Various carbonylic monoterpenoids important for fragrance and pharmaceutical industries can be obtained in good to excellent yields starting from biomass-based monoterpenic alcohols, such as isobomeol, perillyl alcohol, carveol, and citronellol. The catalyst undergoes no metal leaching and can be easily recovered by the application of an external magnet and re-used. (C) 2011 Elsevier Inc. All rights reserved.

Photoluminescence enhancement by gold nanoparticles in Eu(3+) doped GeO(2)-Bi(2)O(3) glasses

We report large photoluminescence (PL) enhancement in Eu(3+)-doped GeO(2)-Bi(2)O(3) glasses containing gold nanoparticles (NPs). Growth of approximate to 1000% in the PL intensity corresponding to the Eu(3+) transition (5)D(0)->(7)F(2), at 614 nm, was observed in comparison with a reference sample that does not contain gold NPs. Other PL bands from 580 to 700 nm are also enhanced. The enhancement of the PL intensity is attributed to the increased local field in the Eu(3+) locations due to the presence of the NPs and the energy transfer from the excited NPs to the Eu(3+) ions.

Supramolecular Approach to Gold Nanoparticle/Triruthenium Cluster Hybrid Materials and Interfaces

A systematic and comprehensive study of the interaction of citrate-stabilized gold nanoparticles with triruthenium cluster complexes of general formula [Ru(3)(CH(3)COO)(6)(L)](+) [L = 4-cyanopyridine (4-CNpy), 4,4`-bipyridine (4,4`-bpy) or 4,4`-bis(pyridyl)ethylene (bpe)] has been carried out. The cluster-nanoparticle interaction in solution and the construction of thin films of the hybrid materials were investigated in detail by electronic and surface plasmon resonance (SPR) spectroscopy, Raman scattering spectroscopy and scanning electron microscopy (SEM). Citrate-stabilized gold nanoparticles readily interacted with [Ru(3)O(CH(3)COO)(6)(L)(3)](+) complexes to generate functionalized nanoparticles that tend to aggregate according to rates and extents that depend on the bond strength defined by the characteristics of the cluster L ligands following the sequence bpe > 4,4`-bpy >> 4-CNpy. The formation of compact thin films of hybrid AuNP/[Ru(3)O(CH(3)COO)(6)(L)(3)](+) derivatives with L = bpe and 4,4`-bpy indicated that the stability/lability of AuNP-cluster bonds as well as their solubility are important parameters that influence the film contruction process. Fluorine-doped tin oxide electrodes modified with thin films of these nanomaterials exhibited similar electrocatalytic activity but much higher sensitivity than a conventional gold electrode in the oxidation of nitrite ion to nitrate depending on the bridging cluster complex, demonstrating the high potential for the development of amperometric sensors.