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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.

A large, two-orders-of-magnitude enhancement of fluorescence emission from cyanobacterial Photosystem I (PSI) coupled to plasmonic excitations in silver island films was observed. Such a high value has not been reported for metal-enhanced fluorescence of photosynthetic pigment-protein complexes before. The dramatic enhancement of the PSI emission occurs when PSI is excited resonantly into the Qx and Qy bands of chlorophyll a. In contrast, excitation in the carotenoid absorption band yields ten times lower enhancement factors. We attribute these large values of enhancement factor to plasmon-induced activation of excitation and emission channels absent for isolated PSI complexes.

Spectrally resolved and kinetic response of electroluminescence was monitored from resistively heated carbon nanotube (CNT) macroassemblies. Sensitive detection system and custom-made setup for high-speed optoelectronic measurements were employed to investigate unsorted and single chirality-enriched CNTs. By increasing the content of (7,6) or (6,5) CNTs in a sample, the E11 emission peak in the infrared region became more narrow (∼150 nm), hence approaching that of commercial emitters for this spectral range. Moreover, electroluminescence initiation in CNTs occurred very rapidly and reached its full intensity within tens of milliseconds. Interestingly, observed delay between bias voltage application and electroluminescence proved triplet-triplet annihilation in the macroscopic assembly of CNTs.

We observe that introducing a layer of reduced graphene oxide between electrochemically deposited gold nanoparticles and natural photosynthetic Fenna–Matthews–Olson (FMO) complex from green sulfur bacteria, results in an increase of the fluorescence emission of the FMO. This increase is not accompanied with any substantial change of the fluorescence dynamics. Our findings indicate that incorporating graphene-based materials in hybrid assemblies yields better performance of such structures, thus holds promise for designing biosensing and optoelectronic devices.

Forscher der LMU Munchen haben gezeigt, dass sich mit Hilfe von Silbernanoteilchen die Effizienz von Lichtsammelkomplexen enorm steigern lasst. Da es sich hierbei um die zentralen Funktionstrager fur das Einsammeln von Licht bei der Photosynthese handelt, konnte diese Entdeckung bedeutsam fur die Entwicklung neuartiger Hybrid-Solarzellen sein.

We investigate the applicability of a corrole molecule, 5,15-bis(pentafluorophenyl)- 10-(4-methylphenyl)-corrole, as a possible fluorescent sensor of oxygen. Upon illumination we observe a strong increase of the fluorescence intensity and the emission spectrum broadens considerably towards a short wavelength range. This behaviour is in contrast to most fluorescent molecules, which typically feature photobleaching. For the corrole studied here, classic photobleaching is observed only when the sample is placed in a vacuum. This unique behaviour of fluorescence emission suggests the use of these molecules in all-optical oxygen sensor architectures.

Light emission from carbon nanotube (CNT) films was explored in both the near-infrared and the infrared spectral regions upon application of external bias voltage. We obviated the need to use sophisticated vacuum apparatus by employing state-of-the-art optics and detection system. It enabled us to sensitively probe electroluminescence at relatively low temperatures (T ∼ 300 °C) in ambient conditions and investigate the character of emission from CNT assemblies in real life conditions. The observed spectral response revealed distinct features and the results strongly suggest that CNT assemblies are promising candidates for optoelectronic applications, particularly in the field of telecommunication.

Optical microscopy and spectroscopy of hybrid nanostructures composed of chlorophyll-containing photosynthetic complexes and silver nanowires reveal strong enhancement of fluorescence intensity of chlorophylls bound to the protein. This effect results from interaction between excited states of molecules embedded in the photosynthetic complex and plasmon excitations in metallic nanowires. Wide-field microscopy images reveal twofold increase of the emission intensity for complexes located at the ends of the nanowires as compared to the ones lying along the nanowires. Complementary spectrally and temporally resolved experiments indicate about 10-fold average increase of the chlorophyll fluorescence rate upon coupling with the metallic nanoparticles.

Plasmonic nanoparticles are commonly used to tune and direct the radiation from electric dipolar emitters. Less progress has been made towards understanding complementary systems of magnetic nature. However, it has been recently shown that high-index dielectric spheres can act as effective magnetic antennas. Here we explore the concept of coupling dielectric magnetic antennas with either an electric or magnetic dipolar emitter in a similar fashion to the purely electric systems reported previously. We investigate the enhancement of radiation from systems comprising admixtures of these electric and magnetic elements and perform a full study of its dependence on the distance and polarization of the emitter with respect to the antenna. A comparison to the plasmon antennas reveals remarkable symmetries between electric and magnetic systems, which might lead to novel paradigms in the design of nanophotonic devices that involve magnetic activity. © 2012 Optical Society of America., Financial support from the ETORTEK 2011 “nanoiker” of the Department of the Industry of the Basque Country Government, the WELCOME program “Hybrid nanostructures as a steppingstone towards efficient artificial photosynthesis” awarded by the Foundation for Polish Science, the Spanish MEC FIS2010-19609-C02-02, Consolider NanoLight (CSD2007-00046) and FIS2009-13430-C02 research grants and the Comunidad de Madrid Microseres-CM Program (S2009/TIC-1476) are gratefully acknowledged. RE and JA acknowledge support from the Spanish National project Euroinvestigación EUI200803816 CUBiHOLE.

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.

Butenandtstrasse 11, D-81377 Munich, Germany Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA Department of Biology and Biotechnology, Ruhr-University Bochum, 44780 Bochum, Germany Department of Biology I–Botany, Ludwig-Maximilian-University, D-80638 Munich, Germany Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia

We study the magnetization dynamics in CdMnTe quantum dots using subwavelength optical microscopy imaging at B=0 T. For continuous laser illumination each dot exhibits strong and unique circular polarization despite completely unpolarized ensemble emission. This implies that after an exciton recombines, the spontaneous ferromagnetic alignment of magnetic impurities persists for over 100 μs, which is a million times longer than in CdMnTe quantum wells. The spin memory effect points toward a qualitatively different picture of magnetization dynamics in the zero-dimensional limit.

Using polarization-resolved photoluminescence imaging in external magnetic fields we measure statistically significant distributions of exchange splitting, diamagnetic shift and effective g-factor of excitons in tens of single CdTe quantum dots. Comparison between the as-grown and annealed structures shows strong suppression of ensemble inhomogeneities, with the average exchange splitting reduced by half and significant narrowing of the g-factor distribution. Remarkably, the average value of the excitonic g-factor remains unchanged. This unique ability to yield highly uniform quantum dot ensembles without hampering the exciton Zeeman splitting makes annealing a highly attractive means for tuning the spin properties of quantum dot excitons.

The authors show that energy transfer is a feasible mechanism for exciting fluorescence of single light-harvesting complexes with different characters of the fluorescing state. This approach is applied for excitons consisting of 18 strongly coupled bacteriochlorophylls in light-harvesting complex 2 as well as for peridinin-chlorophyll-protein monomers containing either two chlorophyll a molecules or a pair of chlorophyll a and chlorophyll b characterized with the emission energy difference of 400cm−1. Using this method the authors are able to observe fluorescence spectral dynamics on the scale comparable or larger than the emission linewidth of a single chromophore.

Resonant Raman scattering is a sensitive means to probe electronic states in semiconductor materials even when such states are not accessible either through photoluminescence or transport techniques. We show that resonant Raman scattering can be used to probe the excited state distribution of CdTe∕ZnTe quantum dots at room temperature. In particular we apply this technique to study the changes of such quantum dots after rapid thermal annealing.

We report on low temperature polarization-resolved imaging of single magnetic self-assembled CdMnTe quantum dots (QDs) in the absence of magnetic field. Using longitudinal optical phonon-assisted absorption to photoexcite spin-polarized excitons into a QD ground state, we find that the magnetic impurities within CdMnTe QDs can be aligned ferromagnetically with a single emission lines exhibiting a circular polarization as large as 65%. These results demonstrate that the magnetization of a single magnetic QD can be optically controlled with a suitably polarized laser.

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.

We use a solid immersion lens to study single magnetic dots with a spatial resolution of 200 nm. The results demonstrate that Mn ions in a single dot can be aligned by optical excitation. This alignment is observed only for the dots resonantly populated via LO phonons

The properties of superlattices consisting of 2 monolayer wide CdTe insertions into ZnTe spacer barriers with thickness ranging from 3 to 75 monolayers are investigated by means of transmission electron microscopy and photoluminescence spectroscopy. We show that quasi zero-dimensional CdTe islands form in this highly lattice-mismatched system. For spacer thickness smaller than 25 monolayers, the islands are vertically correlated along the axis tilted by 40° with respect to the growth direction, while for thicker ZnTe spacers no correlation is observed. The electronic coupling between the correlated islands manifests itself by the appearing of an additional emission band at energies lower to those corresponding to uncorrelated dots. The optical spectroscopy data reveal zero-dimensional localization of excitons by the electronically coupled islands. The decay time of the excitonic recombination is found to be over an order of magnitude longer in the case of the coupled islands than in the case of isolated ones.

We report on single dot photoluminescence imaging and spectroscopy at B=0T on magnetically doped CdMnTe self-assembled quantum dots with average Mn concentration of several percent. Quasi-resonant excitation with circularly polarized laser leads to formation of magnetic polarons with magnetization induced by the laser light. In this case all quantum dots are polarized in the same direction. In contrast, when the dots are populated using above the barrier excitation, with randomly polarized excitons, the resultant magnetization is random and varies from dot to dot. These experiments demonstrate a way to control the magnetization of magnetically doped quantum dots by means of light excitation. In addition, they point towards extremely long spin memory times in these structures, reaching hundreds of microseconds, making CdMnTe quantum dots promising candidates for local magnetic field sources on the nanoscale.

We report on confocal microscopy imaging of hybrid nanostructures composed of silver nanowires and corroles. Both nanomaterials were separated by a 30 nm thick SiO2 spacer in order to inhibit uorescence quenching. The results show that for such a hybrid nanostructure the average enhancement of the uorescence intensity reached 2.5. Importantly, the coupling to plasmon excitations in metallic nanowires leaves no e ect on the uorescence spectrum of the organic molecules.

We demonstrate a way to conjugate a light-harvesting complex, peridinin chlorophyll protein, with silver nanowires using biotin-streptavidin linker. In the case of conjugated structure we observe slight increase of the uorescence intensity of the chlorophyll emission followed by the gradual decrease of the intensity due to photobleaching. For a non-conjugated mixture of peridinin chlorophyll protein with silver nanowires only the photobleaching takes place. The results suggest a possible way to fabricate hybrid nanostructures comprising light-harvesting complexes and metallic nanoparticles for achieving the e cient plasmon-induced enhancement of absorption of the light-harvesting complexes.

Exciton magnetic polarons in CdMnTe QDs form through the spontaneous ferromagnetic alignment of the Mn. We show evidence that after EMP recombination, the Mn magnetization persists, directly impacting the next occupation.

Measurements of optical properties of epitaxially grown CdMnTe quantum dots are presented. Magnetic ions are incorporated into the structure by passivating the substrate surface with Mn prior the quantum dot deposition. As expected, the intensity of intra-Mn transition increases with the time of manganese passivation. The formation of magnetic quantum dots is evidenced by presence of single emission lines in the micro-photoluminescence spectrum. The width of single dot emission lines is much broader than observed for non-magnetic quantum dots. The broadening is caused by thermal fluctuations of magnetization in quantum dots. Resonant spectroscopy results indicate that the exciton-optical phonon scattering is the main energy relaxation mechanism in these structures. The measurements suggest that post-growth thermal processing offers the possibility of tuning the magnetic properties of these structures.

In this work we demonstrate enhancement of the fluorescence collection efficiency for chlorophyll-containing photosynthetic complexes deposited on SiO2 spherical nanoparticles. Microscopic images of fluorescence emission reveal ring-like emission patterns associated with chlorophyll-containing complexes coupled to electromagnetic modes within the silica nanoparticles. The interaction leaves no effect upon the emission spectra of the complexes, and the transient behavior of the fluorescence also remains unchanged, which indicates no influence of the silica nanoparticles on the radiative properties of the fluorophores. We interpret this enhancement as a result of efficient scattering of electromagnetic field by the dielectric nanoparticles that increases collection efficiency of fluorescence emission.