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We observe correlation between the length of surface plasmon polariton propagation in silver nanowires and the enhancement of fluorescence intensity due to coupling with localized plasmon resonance...

Single nanocrystal spectroscopy is employed to demonstrate metal-enhanced optical response of Er3+/Yb3+ doped up-conversion nanocrystals deposited on graphene upon coupling with silver nanowires. Direct interaction between nanocrystals and graphene results in quenching of up-conversion emission and shortening of luminescence decay times, due to the energy transfer to graphene. The amount of the energy absorbed by graphene can be enhanced by coupling Er3+/Yb3+ doped up-conversion nanocrystals with silver nanowires. Microscopy studies with high spatial resolution together with time-resolved analysis of nanocrystal luminescence show increase of the emission rates with fourfold enhancement of the intensity for nanocrystals placed in the vicinity of silver nanowires. This strong enhancement emerges despite simultaneous interaction with graphene. The hybrid nanostructure provides thus a way to combine optical activity of up-conversion nanocrystals and enhancement provided by metallic nanowires with excellent electrical and mechanical properties of graphene.

In this paper, we demonstrate remote activation and detection of the 2-photon up-conversion luminescence via surface plasmon polaritons propagating in a long silver nanowire. The hybrid nanostructure was assembled by locally depositing a submicron droplet of nanocrystal-containing colloidal solution on one of the ends of the metallic nanowire. When – using a classic confocal microscope – the second end of the nanowire, without the nanocrystals, is illuminated with infrared laser light, we observe strong emission from the same end. Therefore, it indicates that surface plasmon polaritons activated with infrared light at the second end of the nanowire propagate along it and can excite nanocrystals in the droplet at the opposite end. Subsequently, the excited nanocrystals up-convert the energy and by launching surface plasmon polaritons can guide the up-converted luminescence back to the starting point. The emergence of this effect is much more pronounced for a laser polarized along the nanowire. The spectral and temporal character of this emission reveals strong interactions between surface plasmon polaritons and electronic states of the nanocrystals. The details of local and non-local aspects of the effects of remote excitation and guiding of energy in a silver nanowire are elucidated using a unique experimental setup, based on two microscope objectives for spatial separation and control of both excitation and emission beams.

We present tip-enhanced upconversion photoluminescence (PL) images of Er(3+)- and Yb(3+)-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip-sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er(3+) in the visible region. Very efficient enhancement of upconversion PL is discussed in the context of the two-photon nature of the excitation process and homoenergy transfer between the ions within the nanocrystals. Comparison between different nanocrystals and tips shows a strong influence of the tip shape on the image contrast that becomes particularly relevant for the larger dimensions of the investigated nanocrystals.

We report a comprehensive study on the influence of solvent and organic ligands on the up-converted emission characteristics of NaYF4 nanowires. We have modified the hydrothermal reaction procedure, and used a “microwave flash heating method” to obtain 1.5 μm long and 100 nm wide up-converting NaYF4 nanowires. As-synthesized particles were dispersed in cyclohexane, and a ligand removal procedure has been performed leading to nanowires soluble in water and heavy water. The infrared emission of Er3+ ions was quenched through coupling to the vibrational modes of water molecules and the values of slopes of double logarithmic plots of power dependencies were changed. Besides the spectroscopic characterization of colloidal solutions of NaYF4 up-converting nanowires, we have also performed single particle studies of steady-state emission and luminescence kinetics. In the case of solvent-free separated particles, the ligand molecules provided the main nonradiative depopulation channels, and efficiently shortened the luminescence lifetimes. The output luminescence color also varied for colloidal solutions and single particle studies, which can be of importance for imaging and single particle tracking applications.

We investigated the angular radiation patterns, a key characteristic of an emitting system, from individual silver nanowires decorated with rare earth ion-doped nanocrystals. Back focal plane radiation patterns of the nanocrystal photoluminescence after local two-photon excitation can be described by two emission channels: excitation of propagating surface plasmons in the nanowire followed by leakage radiation and direct dipolar emission observed also in the absence of the nanowire. Theoretical modeling reproduces the observed radiation patterns which strongly depend on the position of excitation along the nanowire. Our analysis allows us to estimate the branching ratio into both emission channels and to determine the diameter-dependent surface plasmon quasi-momentum, important parameters of emitter-plasmon structures.

Fluorescence spectroscopy is applied to study the influence of plasmon excitations in spherical Au nanoparticles on the optical properties of chlorophyll-containing light-harvesting complexes. The separation between the two nanostructures is controlled via silica layer with varied thickness. We observe strong increase of the emission intensity for a 12- nm-thick spacer and the increase is accompanied with shortening of the fluorescence lifetime, which allows us to separate contributions of absorption and emission rate enhancement. At the same time we find an increase of photobleaching. These findings are interpreted as a result of spectral overlap between plasmon resonance and chlorophyll fluorescence.

We present semiempirical approach based on the Judd–Ofelt theory and apply it for modeling the spectral properties of fluoride glasses activated with the rare earth (RE) ions. This method provide a powerful tool for simulating both ground state absorption (GSA) and excited state absorption (ESA) spectra of RE ions, e.g. Nd3+, Ho3+, Er3+ and Tm3+ in the ZBLAN glass matrix. The results of theoretical calculations correspond to the experimentally measured data. We also demonstrate that the spectra obtained using the presented approach are applicable in the analysis of up-conversion excitation schemes in these optoelectronically relevant materials.

We study the fluorescence properties of peridinin-chlorophyll-protein light-harvesting complex reconstituted with both chlorophyll a and chlorophyll b coupled to spherical gold nanoparticles. Since there is a bidirectional energy transfer between the chlorophylls, the impact of plasmon excitations upon the energy transfer dynamics can be studied in such a hybrid nanostructure. The results show that the emission of both chlorophyll a and chlorophyll b in a reconstituted PCP is strongly enhanced when the light-harvesting complexes are separated from the metallic nanoparticles by a 12-nm-thick SiO2 layer, the average enhancement reaches a factor of 8. The analysis of fluorescence decay curves indicates that the energy transfer between chlorophyll a and chlorophyll b is also influenced by plasmon excitations in gold nanoparticles.

In this work we demonstrate confocal uorescence imaging of hybrid nanostructures composed of silver nanowires and peridinin chlorophyll protein light-harvesting complexes. The length of silver nanowires, which reaches 10 μm, allows for determination of the nanowire position and consequently direct correlation with the uorescence image. In this way we probe the in uence of plasmon induced electromagnetic eld on the uorescence of light-harvesting complexes. When the nanowires are spaced from the light-harvesting complexes by a 10 nm thick dielectric layer, we observe a uorescence enhancement, which depends upon the laser excitation wavelength. The measured enhancement values are 2.5 and 1.9 for 405 nm and 485 nm, respectively. Larger enhancement for the 405 nm excitation is attributed to direct creation of plasmon excitations in the silver nanowires.

Mechanical property measurements were made on used sections of mobile landing surfaces for the vertical take off and landing military aircraft. Additionally, property measurements were made on used sections of anchors used to restrain aircrafts movement during full power engine operations following maintenance. In both cases, the material used was aluminum alloy 6061 in the T6 temper. Tensile, hardness and electrical conductivity tests were performed. The landing surfaces were hollow core; the top portion showed more degradation than the bottom due to the former being in closer proximity to aircraft exhaust gases. The used anchor panels showed significant levels of mechanical degradation, falling well below SAE minimum standards.

Navy AM2 mats are used as portable aircraft landing platforms for the Short Take-off/Vertical Landing (STOVL) aircraft operations. This investigation presents the study performed to determine whether the surface discoloration is a precursor to degradation in the mechanical property of the AM2 mat material. The red discoloration on the mat surfaces had a clear correlation with the decrease in yield strength, ultimate strength, and hardness properties.

An interesting competition between two anti-Stokes emissions has been observed and interpreted in ZBLAN and fluoroaluminate (ALF) glasses activated by Ho3+ and Nd3+ ions, respectively. The intensity of an emission line situated spectrally close to the excitation wavelength, was seen to increase with temperature, whereas the intensity of another, upconverted emission line, in the same conditions, was seen to decrease. Both effects are believed to be caused by the same mechanism, which we have identified as the anti-Stokes multiphonon excitation of the state responsible for the first emission, followed by upconversion of the ESA (excited state absorption) or an energy transfer type process. Analysis of the kinetics of the observed effects enabled us to fit a theoretical model to the experimental data. It appears likely that the described competition may be a universal feature not restricted to the materials described in this work.

We present the excited state absorption (ESA) spectroscopy of ZBLAN:Er 3+ glass. The experimental spectra were measured in broad spectral range (500–1800 nm) by the CW pump-probe technique. Judd–Ofelt (JO) approach was employed to interpret the results and to simulate the ESA spectra which were successfully confronted with the experiment. We also propose a systematic approach for prediction of various types of up-conversion mechanisms such as ESA up-conversion and photon avalanche (PA). Careful investigations were made to indicate possible up-conversion excitation channels in a wide spectral range, from 400 nm up to 2 μm.

3CaO–Ga 2 O 3 –3GeO 2 glass excited state absorption spectra-activated with Ho 3+ (Ho 2 O 3 – 0.7 wt% content) have been measured and analysed. Up-converted emission channels have been identified and the predicted up-converted emission bands have been registered under Ar ion laser ( λ = 488 nm) excitation according to the excited state absorption data. A mechanism of up-converted transitions for Ho 3+ centres in this prototype glass network is proposed on the basis of the obtained results.

The effects of curing temperature, based on new, low-temperature powder coating methods and traditional high-temperature powder coating methods, were studied. Heat-sensitive aluminum alloys (2024-T3, 6061-T6, and 7075-T6) were subjected to two different heat-treatment cycles, which were based on temperatures of 121 and 204 °C. Findings indicate that although both cure temperatures achieved powder coatings adhesion and thickness appropriate for industrial uses, the high-temperature cure treatment negatively affected the mechanical properties.

We present excited state absorption (ESA) spectroscopy of Nd3+-activated fluoroaluminate glass. The ESA spectra were measured in the range from 550 to 1800 nm by the continuous-wave pump-probe technique. Judd–Ofelt (JO) formalism was employed to interpret the results. The obtained intensity parameters and linewidths were used to simulate the ESA spectra, which were successfully compared with the experimental data. The calculated ESA spectra were also used to precisely assign previously observed upconverted emissions and to predict additional ones, which were experimentally verified. The presented upconverted luminescence spectrum contains several anti-Stokes emission lines at 355 nm, 381 nm, 412 nm and 448 nm, and is in good agreement with the calculations.

The broadband optical gain peaking around 1100 nm has been registered in the ZAS glass activated by Cr3+ ions. The gain spectrum spreads over ∼300 nm range and on the short wavelength side it is accompanied by the excited state absorption (ESA) of the maximum around 750 nm. The ZAS glass, being designed as a parent glass for more sophisticated glass ceramic (awaited to be a promising laser medium), contrary to this ceramic, appeared itself to be interesting gain medium.

The purpose of this study was to test the heat resistance of eight different combinations of coatings that are applied on Marine Corps AM2 Al 6061-T6 mats. The objective was to determine which coating is best suited for use on mats exposed to exhaust from short take off and vertical landing aircraft. Each coating combination was first exposed to the flame of three torches from a constant distance for different periods of time. Then, conductivity, hardness, tensile tests and optical microscopy were conducted. The plate with NiAl bond coating, Al2O3–ZrO2 heat resistance coating, and NiCr–SiC non-skid coating outperformed other coating combinations.

Phase-sensitive and frequency-resolved detection techniques are used for the initial state-resolved excited state absorption (ESA) measurements in ZBLAN:Ho3+ glass. Both experimental techniques were applied simultaneously in a broad spectral range (550–1750 nm) for the first time. Estimated results are compared and discussed in detail. A simple kinetic model, used for qualitative considerations, is presented and successfully compared with the experimental data. The measured spectra will be useful for identifying new up-conversion excitation channels in the considered system, where ESA transitions originating from several excited levels are observed.

We describe the optical properties of a simple plasmonic network, which consists of silver nanowires coupled with nanocrystals doped with rare-earth-ions. The nanocrystals exhibit anti-Stokes emission called up-conversion. First of all, we demonstrate efficient coupling between a single silver nanowire and nearby nanocrystals via plasmonic excitations. These plasmonic interactions result in an enhancement of the up-converted emission intensity of nanocrystals located in the close vicinity of the nanowires, mostly due to increased radiative emission rates. We prove that luminescence can be either emitted directly by the nanocrystals or transferred to the nanowire. Imaging of angular-resolved emission patterns in the Fourier plane reveals plasmon-mediated luminescence, where the up-converted radiation is emitted via the nanowire antenna as leakage radiation. The luminescence signal can be distributed by plasmonic network for quite long distances reaching tens of micrometers.

We report on the upconverted luminescence in neodymium-activated fluoroaluminate glass obtained with 800 nm diode laser excitation. Several anti-Stokes emissions: at 588, 607, 720 and 750 nm are observed and appropriate transitions are assigned. For both latter emissions we observe strong dependence on temperature: the 720 nm emission intensity decreases with temperature, whereas the 750 nm emission increases. Interpretations are presented in terms of the influence of oxygen-affected sites on the radiationless transitions and multiphonon anti-Stokes excitation. The models provide reasonable fits to the experimental data.

Used AM2 mats (aircraft landing platforms) composed of Aluminum 6061-T6 were machined into tensile and conductivity bars. Samples were then subjected to five different temperatures: 315.6, 371.1, 426.7, 482.2 and 537.8 °C (600, 700, 800, 900 and 1000 °F), seven different time intervals (10, 20, 30, 70, 90, 120 and 150 s), and eight different exposure times (1, 2, 3, 5, 7, 10, 15 and 20 times). The ultimate strength, yield strength, and percent elongation of the samples were determined. Conductivity and hardness tests were also performed to assess the effect of thermal exposure.

We demonstrate efficient coupling between plasmons in a single silver nanowire and nanocrystals doped with rare earth ions, α-NaYF4:Er(3+)/Yb(3+). Plasmonic interaction results in a sevenfold increase of the up-converted emission of nanocrystals located in the vicinity of the nanowires as well as much faster luminescence decays. The enhancement of the emission can be precisely controlled by the polarization of the excitation laser and is significantly stronger for polarization parallel to the nanowire antennas. Imaging of angular-resolved emission patterns in the Fourier plane reveals plasmon-mediated luminescence, where the up-converted radiation is emitted via the nanowire antennas as leakage radiation.

We studied physical properties of hybrid nanostructures consisting of α-NaYF4:Tm3+/Yb3+ nanocrystals coupled to single silver nanowires. By using confocal fluorescence microscope we observed much higher intensity of the upconversion emission form nanocrystals placed in the vicinity of nanowires as compared to isolated ones. At the same time Fluorescence Life-time Imaging Microscopy demonstrates shortening of the fluorescence decays times for metal-coupled nanocrystals. We conclude that plasmon-enhanced emission rates are mainly responsible for enhanced up-conversion efficiency.

In this paper we demonstrate direct excitation of propagating plasmons in silver nanowires. The plasmons are excited either directly by an infrared excitation or indirectly via up-conversion process in rare-earth doped nanocrystals placed in the vicinity of the silver nanowires. In order to map propagating plasmons in silver nanowires, we designed an experimental setup which enables precise, diffraction-limited focusing of the laser, while at the same time both wide-field and confocal imaging of fluorescence.

Fluorescence imaging of hybrid nanostructures composed of a bacterial light-harvesting complex LH2 and Au nanorods with controlled coupling strength is employed to study the spectral dependence of the plasmon-induced fluorescence enhancement. Perfect matching of the plasmon resonances in the nanorods with the absorption bands of the LH2 complexes facilitates a direct comparison of the enhancement factors for longitudinal and transverse plasmon frequencies of the nanorods. We find that the fluorescence enhancement due to excitation of longitudinal resonance can be up to five-fold stronger than for the transverse one. We attribute this result, which is important for designing plasmonic functional systems, to a very different distribution of the enhancement of the electric field due to the excitation of the two characteristic plasmon modes in nanorods., Research in Poland was supported by the WELCOME project “Hybrid Nanostructures as a Stepping Stone towards Efficient Artificial Photosynthesis” funded by the Foundation for Polish Science and EUROCORES project “BOLDCATS” funded by the European Science Foundation. Part of sample characterization measurements was carried out at the facilities of National Laboratory FAMO in the Institute of Physics, NCU in Torun. We thank Wojciech Zaleszczyk for performing SEM characterization of Au nanorods. THPB thanks the Indonesian Ministry of Research and Technology for SINAS Grant (RT-2012-0264) and the Indonesian Ministry of Education and Culture for the International Research Collaboration Grant (0541/023-04.1.01/00/2012). MKS and JA acknowledge funding from the ETORTEK project nanoiker of the Department of Industry of the Government of the Basque Country, project IT756-13 of the Department of Education and Culture of the Basque Country, scholarship AP-2012-4204 from the Spanish Ministry of Education, Culture and Sport, and the project FIS2010-19609-C02-01 of the Spanish Ministry of Innovation.

International audience; The interaction of thiols (glutathione, cysteine, and cysteamine) with yellow-emitting siloxane-capped ZnO QDs was studied. A gradual enlargement of the PL emission band resulting in white-light emission was observed upon reaction with thiols, while the diameter (ca. 4 nm) and the crystallinity of the dots were not affected. The appearance of broad white-emission was accompanied by a decrease of the photoluminescence quantum yield from 16% to 5-6%. Generation of surface defect states through interaction of the thiols with Zn surface atoms of the dots provoking shrunk of the siloxane capping may be responsible of that broadband emission throughout most of the light spectrum.

We show that the fluorescence of peridinin-chlorophyll a-protein complexes can be strongly enhanced via coupling with plasmon excitations localized in metal nanostructures. The results of ensemble and single-molecule spectroscopy experiments at room temperature demonstrate six-fold increase of the emission intensity of the light-harvesting complex when it is placed in the vicinity of chemically prepared silver islands. Irrespective of the enhancement, we observe no effect of the metal nanoparticle on the fluorescence emission energy of the complex. This observation implies that plasmon excitations may be applied for controlling the optical properties of complex biomolecules.

We report on single nanocrystal fluorescence microscopy of blends composed of colloidal up-converting NaYF4 nanocrystals doped with rare-earth ions embedded in poly(3-hexylthiophene) (P3HT) polymer. By probing both steady-state and time-resolved fluorescence properties of individual nanocrystals excited with infra-red 980 nm laser, we demonstrate that upon up-conversion to the visible spectral range, the energy is efficiently transferred from the nanocrystals to P3HT. From the analysis of fluorescence lifetimes, the energy transfer efficiency for 550 nm emission of the nanocrystals was estimated to be 60%. This observation renders the up-converting nanocrystals as potential structures for improving light-harvesting efficiency of polymers in the near-infrared spectral region.

The influence of plasmon excitations in spherical gold nanoparticles on the optical properties of a light-harvesting complex 2 (LH2) from the purple bacteria Rhodopseudomonas palustris has been studied. Systematic analysis is facilitated by controlling the thickness of a silica layer between Au nanoparticles and LH2 complexes. Fluorescence of LH2 complexes features substantial increase when these complexes are separated by 12 nm from the gold nanoparticles. At shorter distances, non-radiative quenching leads to a decrease of fluorescence emission. The enhancement of fluorescence originates predominantly from an increase of absorption of pigments comprising the LH2 complex.

A competition between two anti-Stokes emissions has been observed and interpreted in ZBLAN glass activated by Ho(3+) ions. The first anti-Stokes emission intensity was seen to increase with temperature, whereas another, upconverted emission, was seen to decrease under the same conditions. Both observed tendencies are believed to be caused by the same effect: the multiphonon anti-Stokes excitation of the state responsible for the first emission. Analysis of the kinetics and fits of the theoretical model to experimental data are presented.

The excited state absorption (ESA) spectra of ZBLAN glass activated by trivalent holmium ions have been measured in a wide spectral range (550–1750 nm) and simulated using such theoretical tools as the Judd–Ofelt formalism and McCumber theory of stimulated emission. We also propose a systematic approach for prediction of various types of up-conversion mechanisms in a given type of material. Experimental results on ESA up-conversion processes in ZBLAN:Ho3+ under red and infrared laser excitation, which confirm theoretical analysis, are presented. The optical linewidths were studied using high resolution laser spectroscopy at low temperatures and the existence of different crystallographic sites for Ho3+ ions was revealed.

We report on experimental and theoretical studies of plasmon-induced effects in a hybrid nanostructure composed of light-harvesting complexes and metallic nanoparticles in the form of semicontinuous silver film. The results of continuous-wave and time-resolved spectroscopy indicate that absorption of the light-harvesting complexes is strongly enhanced upon coupling with the metallic film spaced by 25 nm of a dielectric silica layer. This conclusion is corroborated by modeling, which confirms the morphology of the silver island film.

A sort of nontrivial competition between the excited state absorption (ESA) and optical gain is shown and interpreted for 9 m-long optical fiber. Using a typical SiO2:Nd3+ fiber we observe an interesting nonmonotonic dependence of the gain on signal (probe beam) intensity with substantial contribution of the ESA. This behavior is simulated via kinetic analysis.