Ag Aggregates Research Articles

Plasmonic Ag Nanoparticles: Correlating Nanofabrication and Aggregation for SERS Detection of Thiabendazole Pesticide.

The level of aggregation and aggregate morphology of metallic nanoparticles are factors that influence the SERS signal (surface-enhanced Raman scattering), affecting reproducibility and sensitivity. This study presents a systematic evaluation of the colloidal aggregation on the SERS signal by combining transmission electron microscopy and UV-vis extinction spectroscopy. It focuses on the effect of two methods of sample preparation ("external standard method-ESM" and "standard addition method-SAM") on the SERS signal using the fungicide thiabendazole (TBZ) in Ag colloid as a probe molecule. The TBZ critical concentration (concentration for which SERS reaches the maximum intensity) was 6.0 × 10-6 mol/L for ESM and 1.5 × 10-6 mol/L for SAM. Besides, TBZ exhibited a sigmoid-type isotherm for ESM, indicating formation of a TBZ first layer on Ag nanoparticles at lower concentrations (Ag aggregates more compact; size <500 nm) and TBZ multilayers at higher concentrations (Ag aggregates more branched; >2 μm). For SAM, the TBZ first layer formation was also observed at lower concentrations (Ag aggregates more branched; <2 μm). However, at higher concentrations, the Ag colloid degradation/precipitation was observed (Ag aggregates more compact; >2 μm). The Ag aggregation mechanisms align with reaction-limited colloidal aggregation at lower concentrations and diffusion-limited colloidal aggregation at higher concentrations. We believe these results contribute to the SERS research field despite all of the work already done over its 50-year history.

Effect of NiAl alloy microparticles deposited in flexible SERS substrates on the limit of detection of rhodamine B molecules.

Flexible-SERS (FSERS) substrates were fabricated by depositing Ni64Al36(NiAl)-alloy-microparticles and/or spherical Ag-NPs (sizes of 10-40 nm) on recycled plastics, which had an aluminum layer on their surface. First, FSERS substrates made of Al + Ag-NPs and an area of 1 cm2 were used to detect rhodamine B (RhB) molecules. The limit-of-detection (LOD) for RhB was 8.35 × 10-22 moles (∼503 molecules), and the enhancement factor (EF) was 3.11 × 1015. After adding NiAl-microparticles to the substrate, the LOD decreased to 8.35 × 10-24 moles (∼5 molecules) and the EF was increased to 2.05 × 1017. Such EF values were calculated with respect to substrates made only with Al + NiAl-alloy (without Ag-NPs), which did not show any Raman signal. Other FSERS substrates were made with graphene-layer + Ag-NPs or graphene-layer + NiAl-alloy + Ag-Nps, and the best LOD and EF values were 8.35 × 10-22 moles and 6.89 × 1015, respectively. Overall, combining the Ag-NPs and NiAl-alloy microparticles allowed for the zeptomole detection of RhB. This was possible due to the formation of Ag aggregates around the alloy microparticles, which enhanced the number of hotspots. If no alloy is present in the FSERS substrates, the detection of RhB is lowered. Overall, we presented a low-cost FSERS substrate that does not require expensive Au films or Au-NPs (as previously reported) to detect RhB at the zeptomole level.

Synthesis and characterization of Ag@M-BTC (M = Zn & Cd) Nanocomposites for efficient removal of methylene blue and indigo carmine

Two MOF based composite materials decorated with Ag NPs viz. Ag@M-BTC (BTC= 1,3,5-benzenetricarboxylate; M=Zn & Cd) were synthesised and characterized using various physicochemical techniques, including FT-IR, PXRD, FE-SEM, EDX, HR-TEM, BET and XPS. The FT-IR spectra of the nanocomposites (NCs) and the pristine MOFs suggest retention of the MOF structure in the resulting composite materials and the PXRD patterns confirm the presence of metallic Ag within the crystalline phase of the MOFs. The observed rough surfaces on the NCs as evidenced from FE-SEM micrographs, indicates the deposition of Ag NPs on the surface of the MOFs. Furthermore, HR-TEM images reveal the presence of nanosized Ag aggregates of spherical shape inside the MOF matrix as well as on the surface. The adsorption activity of the synthesised NCs have been assessed for Methylene Blue (MB) and Indigo Carmine (IC). It is observed that the NCs, Ag@Zn-BTC (1a) and Ag@Cd-BTC (2a) performs better degradation as compared to that of pristine MOFs. These NCs can degrade MB completely (100 %) after 50 min treatment time, while maximum 91 % degradation was recorded for the IC dye. Here, the degradation process can be thought of as operating via chemisorption phenomena, supported by theoretical calculations. Additionally, these NCs can be reused up-to three times for the effective degradation of dyes.

Probing the structural and spectroscopic characteristics of Ag2O-modified Li2O–CaO–B2O3 glasses doped with Nd2O3

Currently, there is growing interest in Ag2O doping in oxide glasses through optimal selection of excitation wavelengths to achieve efficient luminescence via either up or down-conversion processes. In this present work, we report the influence of Ag nanoparticles/aggregates on the structural and spectroscopic characteristics of melt-quenched Ag2O - co-doped (19.5-x)Li2O+70B2O3+10CaO+0.5Nd2O3+xAg2O glasses. Systematic studies were conducted using XRD, Raman spectroscopy, HR-TEM, MAS-NMR, UV–Visible–NIR, Photoluminescence, and decay kinetics techniques. The XRD analysis conclusively indicates the absence of crystalline peaks. However, HR-TEM analysis showed a reduction in the size of AgNPs from 14 nm to 11 nm with an increase of Ag2O concentration from 0.25 mol% to 0.5 mol%, respectively. The RAMAN and MAS-NMR (11B and 7Li) revealed the modification in the local structure induced by the Ag2O as revealed by the predominant borate structural units, and silver (Ag) acted as a modifier in the glass matrix. The absorption spectra of all samples exhibit a characteristic peak of Nd3+ ions. Interestingly, the LCBNd0.5Ag0.5 glass sample exhibits the SPR peak at 416 nm, indicating that the lower limit of Ag2O in LCBNd0.5 is <0.5 mol%. Luminescence studies at different excitation wavelengths (350, 525, and 584 nm) reveal the predominant emission at 877 nm and 1058 nm, whose emission intensity increased with Ag2O concentration. Samples with Ag2O-doped LCBNd glasses exhibit identical lifetime values, indicating the absence of luminescence-quenching and the presence of Ag aggregates leading to the SPR effect. Based on our findings, the LCBNd0.5Ag0.5 sample demonstrated superior performance to other samples, with the highest emission under an excitation of 350 nm.

Experimental and Theoretical Studies on Ag Nanoparticles with Enhanced Plasmonic Response, Formed Within Al2O3 Thin Films Deposited by Magnetron Sputtering

AbstractReactive magnetron sputtering was employed to prepare nanocomposite thin films of Ag/Al2O3, on a glass substrate. The films are characterized by the formation of Ag nanoparticles embedded in the Al2O3 matrix, after thermal treatment at 600 °C, which are responsible for the appearance of an outstanding pronounced and narrow localized surface plasmon resonance (LSPR) band. Electron microscopy analysis also revealed the presence of larger Ag fractal aggregates at the film’s surface, responsible for a broad band absorption. Noteworthily, the LSPR band maximum remains at the same position (about 412 nm) for Ag concentrations ranging from 23 to 34 at.%, despite some discernible alterations in both LSPR band intensity and width. An optimized thin film is characterized by full transparency in non-resonant wavelengths due to suppression of Ag aggregates at the film’s surface, while maintaining the LSPR behavior. To better explain the plasmonic behavior of the Ag/Al2O3 films, discrete dipole approximation was used to determine the extinction, scattering, and absorption efficiencies of Ag spheres surrounded by an Al2O3 cap layer. This allowed to ascertain some nanostructural features of the films, pointing to the formation of Ag nanoparticles with average sizes in the order of 40 nm.

Luminescent Au(III)-M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions†.

The syntheses and structures of a series of complexes based on the C∧C-chelated Au(III) unit (C∧C = 4,4'-bis(t-butyl) 2,2'-biphenyl-1,1'-diyl) are reported, namely, [{(C∧C)Au(C≡CtBu)2}2M2], (C∧C)Au(C≡CR)(C≡NXyl), and [{(C∧C)Au(C≡CR)2}{M(C≡NXyl)}] (M = Ag, Cu; R = tBu, C6H4tBu-4, C6H4OMe-4; Xyl = 3,5-Me2C6H3). The X-ray structures reveal a broad range of dispositions determined by the different coordination modes of Ag(I) or Cu(I). The complexes are bright photoemitters in the solid state and in poly(methyl methacrylate) (PMMA) films. The photoluminescence is dominated by 3IL(C∧C) transitions, with indirect effects from the rest of the molecules, as supported by theoretical calculations. This work opens up the possibility of accessing Au(III) carbon-rich anions to construct photoluminescent aggregates.

Monitoring Ag nanoparticles growth in undoped and Er3+-doped glasses by in-situ UV–Vis spectroscopy and its luminescent properties

Heavy metal germanate glass compositions containing silver and erbium were prepared using the melt-quenching methodology. Ag nanoparticle formation was achieved by controlled thermal treatment and the growth was monitored by in-situ UV–Vis spectroscopy. After treatment, TEM images revealed that Ag nucleation begins after 60 min reaching an average size of 4.3 nm after 210 min. The photoluminescent properties were studied through nanoclusters Ag emission and visible upconversion of Er3+, which point out a clear dependence on the Ag nanoparticles size on the luminescent properties of the material. Furthermore, Judd–Ofelt parameters were calculated and significantly varied in respect to Ag addition and heat treatment conditions, corroborating with the proposed tunable emission, and the presence of Ag aggregates. Therefore, these results highlight the importance of the Ag nanoparticles size to control the luminescent properties of these glasses, demonstrating their potential for development of optical applications including white and green/red tunable emitting devices.

A porphyrin-based ratiometric SERS sensor for high-throughput and ultrasensitive cadmium ion detection.

We propose a novel method for highly sensitive SERS detection of Cd2+ ions based on TMPyP-triggered Ag aggregates, which is achieved via a simple electrostatic interaction. In particular, this sensing system is relatively simple, but provides high sensitivity and excellent selectivity in a high-throughput fashion.

Tunable and high-color-rendering white light emissions in full visible spectral range in Ag-aggregates/Sm3+ co-doped germanate glass fluorophors

To achieve a tunable and high-color-rendering white light emission in full visible spectral range, the Ag-aggregates/Sm3+ co-doped germanate glass fluorophors were prepared by a melt-quenching method. Under the excitation of different wavelengths, the intense broadband emissions covering full visible spectral range from blue to red were gained in the germanate glasses only containing Ag-aggregates. From the optical spectral analyses, it was found that with increasing the excitation wavelengths, the emission peak position exhibits red-shift. However, the red component in the emission spectra is still of relative lack for realizing high quality white light, therefore Sm3+ was introduced as co-dopant to supply the red spectral component. In this way, a series of chroma-tunable and full-color-emitting white lights with color coordinates from (0.26, 0.25) to (0.30, 0.32) were successfully realized based on adjusting the excitation wavelengths and Sm3+ concentration. Particularly, the color rendering index (CRI) up to 97.6 was achieved. Furthermore, the luminescence thermal stability of Ag-aggregates/Sm3+ co-doped germanate glass fluorophors was investigated based on the Arrhenius model, and the corresponding ΔE values for Ag aggregates and Sm3+ emissions were confirmed to be 0.25 and 0.19 eV, respectively. In addition, a temperature sensing model was established based on the luminescence intensity ratio of Ag-aggregates to Sm3+, and the thermochromatic property of Ag-aggregates/Sm3+ co-doped germanate glasses was also evaluated. It was found that the luminescence color coordinates of Ag-aggregates/Sm3+ co-doped glass fluorophors always lie in the white light region when the sample temperature increases from 301 to 693 K, thus indicating that Ag-aggregates/Sm3+ co-doped glass fluorophors have potential application in solid-state lighting sources as a single-component white lighting material.

Effect of silver co-doping on luminescence of the Pr3+-doped lithium tetraborate glass

Spectroscopic and luminescent properties of the Pr-doped and Pr–Ag co-doped borate glasses with Li2B4O7 (Li2O–2B2O3) composition are studied and discussed. Experimental and theoretical oscillator strengths (fexp and ftheor), phenomenological parameters (Ω2, Ω4, Ω6), radiative properties (Arad, β, τrad), and quantum efficiencies (η) of the Pr3+ luminescence were calculated basing on the obtained experimental results and Judd–Ofelt theory. Most intense band of the Pr3+ luminescence is peaked at 601 nm (1D2 → 3H4 transition). Presence of the isolated Ag+ (4d10, 1S0) ions, small non-plasmonic Ag aggregates (Agmn+ nanoclusters), and plasmonic Ag metallic nanoparticles in the Li2B4O7:Pr,Ag glass was proposed basing on analysis of the photoluminescence and optical absorption spectra. Observed enhancement of luminescence intensity and increasing of stimulated emission cross-section and quantum efficiency of luminescence in the Li2B4O7:Pr,Ag glass is explained by energy transfer from Ag species to the Pr3+ ions as wells local-field effect induced by Ag nanoparticles.

The Role of Substrate on Thermal Evolution of Ag/TiO2 Nanogranular Thin Films.

In multicomponent thin films, properties and functionalities related to post-deposition annealing treatments, such as thermal stability, optical absorption and surface morphology are typically rationalized, neglecting the role of the substrate. Here, we show the role of the substrate in determining the temperature dependent behaviour of a paradigmatic two-component nanogranular thin film (Ag/TiO2) deposited by gas phase supersonic cluster beam deposition (SCBD) on silica and sapphire. Up to 600 °C, no TiO2 grain growth nor crystallization is observed, likely inhibited by the Zener pinning pressure exerted by the Ag nanoparticles on the TiO2 grain boundaries. Above 600 °C, grain coalescence, formation of However, the two substrates steer the evolution of the film morphology and optical properties in two different directions. anatase and rutile phases and drastic modification of the optical absorption are observed. On silica, Ag is still present as NPs distributed into the TiO2 matrix, while on sapphire, hundreds of nm wide Ag aggregates appear on the film surface. Moreover, the silica-deposited film shows a broad absorption band in the visible range while the sapphire-deposited film becomes almost transparent for wavelengths above 380 nm. We discuss this result in terms of substrate differences in thermal conductivity, thermal expansion coefficient and Ag diffusivity. The study of the substrate role during annealing is possible since SCBD allows the synthesis of the same film independently of the substrate, and suggests new perspectives on the thermodynamics and physical exchanges between thin films and their substrates during heat treatments.

Detection of Silver Nanoparticles in Seawater Using Surface-Enhanced Raman Scattering.

Nanomaterials significantly contribute to the development of new solutions to improve consumer products properties. Silver nanoparticles (AgNPs) are one of the most used, and as human exposure to such NPs increases, there is a growing need for analytical methods to identify and quantify nanoparticles present in the environment. Here we designed a detection strategy for AgNPs in seawater using surface-enhanced Raman Scattering (SERS). Three commercial AgNPs coated with polyvinylpyrrolidone (PVP) were used to determine the relative impact of size (PVP-15nmAgNPs and PVP-100nmAgNPs) and aggregation degree (predefined Ag aggregates, PVP-50–80nmAgNPs) on the SERS-based detection method. The study of colloidal stability and dissolution of selected AgNPs into seawater was carried out by dynamic light scattering and UV-vis spectroscopy. We showed that PVP-15nmAgNPs and PVP-100nmAgNPs remained colloidally stable, while PVP-50–80nmAgNPs formed bigger aggregates. We demonstrated that the SERS-based method developed here have the capacity to detect and quantify single and aggregates of AgNPs in seawater. The size had almost no effect on the detection limit (2.15 ± 1.22 mg/L for PVP-15nmAgNPs vs. 1.51 ± 0.71 mg/L for PVP-100nmAgNPs), while aggregation caused an increase of 2.9-fold (6.08 ± 1.21 mg/L). Our results demonstrate the importance of understanding NPs transformation in seawater since this can influence the detection method performance.

A Three-Dimensional Printable Liquid Metal-Like Ag Nanoparticle Ink for Making a Super-Stretchable and Highly Cyclic Durable Strain Sensor.

Fabrication of metal nanoparticle (NP)-based strain sensors with both a broad working range and linearity range is still a significant challenge. Typically, homogeneous conductive percolation networks are indispensable for linear sensing performance, whereas inhomogeneous microstructures may inevitably arise under large strain due to the formation of defects in rigid NPs. In this study, a sandwich-structured strain sensor with an extraordinarily large stretchability (800%) yet self-healing property is fabricated by three-dimensional printing using a liquid metal-like Ag NP ink. The strain sensor shows an initial conductivity of 248 S cm-1, a good linearity in two strain ranges, and a long-term stability after undergoing 5000 cycles under a strain level of 100%. Such highly comprehensive sensing performance is attributed to the unique structure of the Ag NP ink, in which Ag NPs coalesce together after room-temperature sintering triggered by chlorides, and then, the sintered Ag aggregates tend to form continuous conductive networks through hydrogen bonds between polyacrylic acid and carboxymethylcellulose. Further, the free flow of Ag aggregates is the root cause that leads to the change of relative resistance as demonstrated by finite element simulation. This Ag NP-based strain sensor shows high potential for application in monitoring human knuckle motion.

Spectroscopic and luminescent properties of the lithium tetraborate glass co-doped with Nd and Ag

Spectroscopic and luminescent properties of the Nd-doped and Nd–Ag co-doped borate glasses with Li2B4O7 (Li2O–2B2O3) basic composition are investigated and analysed using optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics) experimental methods and Judd–Ofelt analysis. Optical absorption, photoluminescence spectra and decay kinetics of Nd3+ ions were registered and detailed analysed. Experimental and theoretical oscillator strengths (fexp and ftheor), Judd–Ofelt intensity parameters (Ω2, Ω4, Ω6), and important to laser applications radiative parameters such as probabilities of radiative transitions (Arad), branching ratios of luminescence (β), radiative lifetimes (τrad), emission cross-sections (σem), and quantum efficiency (η) of the Nd3+ luminescence in the Li2B4O7:Nd and Li2B4O7:Nd,Ag glasses have been calculated. Broad absorption band of surface plasmon resonance (SPR) related to silver nanoparticles was observed in the Li2B4O7:Nd,Ag glass. Presence of the Ag paramagnetic centres and aggregates in the Li2B4O7:Nd,Ag glass was confirmed by EPR spectroscopy. Photoluminescence emission and excitation spectra as well as decay kinetics of the Ag+ ions and small non-plasmonic Ag aggregates or nanoclusters were registered and discussed. Observed enhancement of the Nd3+ luminescence intensity in the Li2B4O7:Nd,Ag glass is explained by effects induced by SPR of the Ag nanoparticles as wells energy transfer from Ag+ ions and Ag aggregates to the Nd3+ ions.

Plasmonic effect of diffused Ag nanoparticles in EB evaporated Ag/TiO2 bilayer thin films and role of oxygen pressure

Oxygen pressure mediated interfacial diffusion of silver up to top surface of thick (∼120 nm) TiO2 layer in e-beam evaporated Ag/TiO2 bilayer thin films has been observed. This effect has been investigated in oxygen pressure range of 5.9 × 10−5-5.8 × 10−4 mbar during evaporation. The amount of Ag diffusion (5–24%) has been found to be correlated with the induced porosity of TiO2 layer. Both compositional and structural characterizations confirm Ag0 chemical state of diffused silver. Scanning Electron Microscopy revealed Ag aggregates having an approximate average diameter of ∼4 nm and ∼24 nm on top surface. Spectroscopic ellipsometry analysis demonstrates that plasmonic absorption caused by these Ag nanoparticles manifests significant modulation of effective complex refractive indices (ECRI) of TiO2 layer. Specifically, the imaginary part of ECRI of TiO2 exhibits substantial non-zero value (∼6.5 × 10−2) in the visible wavelength range which is otherwise close to zero (<10−5) for intrinsic TiO2 thin film. Finally, the optical role of diffused silver on wavelength and peak of interference absorption in Ag/TiO2 bilayer thin film system has been demonstrated. This investigation gives insight on plasmonic contribution of diffused Ag nanoparticles and its consequence on ECRI of dielectric thin film due to in-situ e-beam evaporation without any post deposition treatment.

Spectroscopic and luminescent properties of the lithium tetraborate glass co-doped with Tm and Ag

Spectroscopic properties of the Tm3+ (4f12, 3H6) ions in Tm-doped and Tm–Ag co-doped glasses with Li2B4O7 (or Li2O–2B2O3) basic composition are studied. All investigated glasses show intense blue, red, and infrared emission bands of the Tm3+ ions. Experimental and theoretical oscillator strengths (fexp and fcal), Judd–Ofelt intensity parameters (Ω2, Ω4, Ω6) and radiative properties such as probabilities of radiative transition (Arad), branching ratios (β), radiative lifetimes (τrad), and quantum efficiencies (η) of the Tm3+ luminescence in the Li2B4O7:Tm and Li2B4O7:Tm,Ag were calculated. Presence of the Ag0 (4d105s1, 2S1/2) and Ag2+ (4d9, 2D5/2) paramagnetic centres and their aggregates in the Li2B4O7:Tm,Ag glass was confirmed by electron paramagnetic resonance. Luminescence spectra and decay kinetics of the Ag+ (4d10, 1S0) ions and small non-plasmonic Ag aggregates were registered and discussed. Increasing of quantum efficiency and yield of the Tm3+ luminescence in the Li2B4O7:Tm,Ag glass is explained by energy transfer from Ag species to the Tm3+ ions.

Deposition of Ag Films on Liquid Substrates via Thermal Evaporation for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman scattering (SERS) substrates were prepared by depositing Ag atoms on liquid surfaces via thermal evaporation at room temperature. These free-sustained substrates result in the formation of uniform Ag films, in which ramified Ag aggregates consist of substantial Ag nanoclusters with narrow gaps of several nanometers in between. SERS spectra of rhodamine 6G were investigated for this substrate to evaluate the SERS performance of this characteristic film morphology, and the results indicated that the SERS intensity from the closely-packed Ag nanostructures and small intervals were significantly enhanced. The dependence of SERS enhancement on the film thickness, nanoparticle size, and gap width was studied. An analytical model was proposed to simulate the electric field distribution during SERS detection, and the results validated the experimental observations.

Ag-Sensitized NIR-Emitting Yb3+-Doped Glass-Ceramics

The optical photoluminescent (PL) emission of Yb3+ ions in the near infrared (NIR) spectral region at about 950–1100 nm has many potential applications, from photovoltaics to lasers and visual devices. However, due to their simple energy-level structure, Yb3+ ions cannot directly absorb UV or visible light, putting serious limits on their use as light emitters. In this paper we describe a broadband and efficient strategy for sensitizing Yb3+ ions by Ag codoping, resulting in a strong 980 nm PL emission under UV and violet-blue light excitation. Yb-doped silica–zirconia–soda glass–ceramic films were synthesized by sol-gel and dip-coating, followed by annealing at 1000 °C. Ag was then introduced by ion-exchange in a molten salt bath for 1 h at 350 °C. Different post-exchange annealing temperatures for 1 h in air at 380 °C and 430 °C were compared to investigate the possibility of migration/aggregation of the metal ions. Studies of composition showed about 1–2 wt% Ag in the exchanged samples, not modified by annealing. Structural analysis reported the stabilization of cubic zirconia by Yb-doping. Optical measurements showed that, in particular for the highest annealing temperature of 430 °C, the potential improvement of the material’s quality, which would increase the PL emission, is less relevant than Ag-aggregation, which decreases the sensitizers number, resulting in a net reduction of the PL intensity. However, all the Ag-exchanged samples showed a broadband Yb3+ sensitization by energy transfer from Ag aggregates, clearly attested by a broad photoluminescence excitation spectra after Ag-exchange, paving the way for applications in various fields, such as solar cells and NIR-emitting devices.

Processes underlying the laser photochromic effect in colloidal plasmonic nanoparticle aggregates**Project funded by the Russian Foundation for Basic Research, the Government of the Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science (Grant 18-42-243023), the RF Ministry of Science and Higher Education, and the State Contract with Siberian Federal University for Scientific Research. A.E. thanks the grant of the President of

We have studied the dynamic and static processes occurring in disordered multiparticle colloidal Ag aggregates with natural structure and affecting their plasmonic absorption spectra under pico- and nanosecond pulsed laser radiations, as well as the physical origin responsible for these processes. We have shown that depending on the duration of the laser pulse, the mechanisms of laser modification of such aggregates can be associated both with changes in the resonant properties of the particles due to their heating and melting (picosecond irradiation mode) and with the particle shifts in the resonant domains of the aggregates (nanosecond pulses) which depend on the wavelength, intensity, and polarization of the radiation. These mechanisms result in formation of a narrow dip in the plasmonic absorption spectrum of the aggregates near the laser radiation wavelength and affect the shape and position of the dip. The effect of polydispersity of nanoparticle aggregates on laser photochromic reaction has been studied.

Concentrated Ag Nanoparticles in Dodecane as Phase Change Materials for Thermal Energy Storage

Silver colloids with concentrations of up to 0.1 M Ag, mass fraction = 1.3%, were prepared in dodecane and eicosane via the thermal reduction of silver neodecanoate using oleoyl sarcosine as a particle stabilizer. The dodecane colloids contained mainly spherical crystallites of fcc Ag with an average diameter of 5 nm, which despite their high concentration have remained stable against precipitation for over two years at room temperature. Images from CitoViva and transmission electron microscopies showed that the small Ag crystallites coexisted with larger particle aggregates. Colloids made in dodecane exhibited thermal conductivities that increased slightly with raising both the Ag concentration and the temperature up to 13.8% at [Ag] = 80 mM, mass fraction = 1%. These modest thermal conductivity enhancements are consistent with predictions based on classical formulations and imply that the Ag aggregates played no role at expediting heat transport. Kinetic data from the particle formation process indicated that the neodecanoate ligand served as an electron donor during the thermal reduction of Ag(I). Optical signals in the visible range generated during the initial stages of particle formation evolved into stronger absorptions upon exposure to ambient light. The optical signals persisted for days under air and seemed to originate from photochemically generated Ag clusters.