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Liu W, Herrmann AK, Bigall NC, Rodriguez P, Wen D, Oezaslan M, Schmidt TJ, Gaponik N, Eychmüller A. Noble metal aerogels-synthesis, characterization, and application as electrocatalysts. Acc Chem Res 2015; 48:154-62. [PMID: 25611348 PMCID: PMC4578670 DOI: 10.1021/ar500237c] [Citation(s) in RCA: 165] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
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Metallic and catalytically active materials with high surface area
and large porosity are a long-desired goal in both industry and academia.
In this Account, we summarize the strategies for making a variety
of self-supported noble metal aerogels consisting of extended metal
backbone nanonetworks. We discuss their outstanding physical and chemical
properties, including their three-dimensional network structure, the
simple control over their composition, their large specific surface
area, and their hierarchical porosity. Additionally, we show some
initial results on their excellent performance as electrocatalysts
combining both high catalytic activity and high durability for fuel
cell reactions such as ethanol oxidation and the oxygen reduction
reaction (ORR). Finally, we give some hints on the future challenges
in the research area of metal aerogels. We believe that metal aerogels
are a new, promising class of electrocatalysts for polymer electrolyte
fuel cells (PEFCs) and will also open great opportunities for other
electrochemical energy systems, catalysis, and sensors. The
commercialization of PEFCs encounters three critical obstacles,
viz., high cost, insufficient activity, and inadequate long-term durability.
Besides others, the sluggish kinetics of the ORR and alcohol oxidation
and insufficient catalyst stability are important reasons for these
obstacles. Various approaches have been taken to overcome these obstacles,
e.g., by controlling the catalyst particle size in an optimized range,
forming multimetallic catalysts, controlling the surface compositions,
shaping the catalysts into nanocrystals, and designing supportless
catalysts with extended surfaces such as nanostructured thin films,
nanotubes, and porous nanostructures. These efforts have produced
plenty of excellent electrocatalysts, but the development of multisynergetic
functional catalysts exhibiting low cost, high activity, and high
durability still faces great challenges. In this Account, we
demonstrate that the sol–gel process
represents a powerful “bottom-up” strategy for creating
nanostructured materials that tackles the problems mentioned above.
Aerogels are unique solid materials with ultralow densities, large
open pores, and ultimately high inner surface areas. They magnify
the specific properties of nanomaterials to the macroscale via self-assembly,
which endow them with superior properties. Despite numerous investigations
of metal oxide aerogels, the investigation of metal aerogels is in
the early stage. Recently, aerogels including Fe, Co, Ni, Sn, and
Cu have been obtained by nanosmelting of hybrid polymer–metal
oxide aerogels. We report here exclusively on mono-, bi- and multimetallic
noble metal aerogels consisting of Ag, Au, Pt, and Pd and their application
as electrocatalysts.
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Selzer F, Weiss N, Kneppe D, Bormann L, Sachse C, Gaponik N, Eychmüller A, Leo K, Müller-Meskamp L. A spray-coating process for highly conductive silver nanowire networks as the transparent top-electrode for small molecule organic photovoltaics. NANOSCALE 2015; 7:2777-2783. [PMID: 25584968 DOI: 10.1039/c4nr06502f] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present a novel top-electrode spray-coating process for the solution-based deposition of silver nanowires (AgNWs) onto vacuum-processed small molecule organic electronic solar cells. The process is compatible with organic light emitting diodes (OLEDs) and organic light emitting thin film transistors (OLETs) as well. By modifying commonly synthesized AgNWs with a perfluorinated methacrylate, we are able to disperse these wires in a highly fluorinated solvent. This solvent does not dissolve most organic materials, enabling a top spray-coating process for sensitive small molecule and polymer-based devices. The optimized preparation of the novel AgNW dispersion and spray-coating at only 30 °C leads to high performance electrodes directly after the deposition, exhibiting a sheet resistance of 10.0 Ω □(-1) at 87.4% transparency (80.0% with substrate). By spraying our novel AgNW dispersion in air onto the vacuum-processed organic p-i-n type solar cells, we obtain working solar cells with a power conversion efficiency (PCE) of 1.23%, compared to the air exposed reference devices employing thermally evaporated thin metal layers as the top-electrode.
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53
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Hatami S, Würth C, Kaiser M, Leubner S, Gabriel S, Bahrig L, Lesnyak V, Pauli J, Gaponik N, Eychmüller A, Resch-Genger U. Absolute photoluminescence quantum yields of IR26 and IR-emissive Cd(1-x)Hg(x)Te and PbS quantum dots--method- and material-inherent challenges. NANOSCALE 2015; 7:133-143. [PMID: 25407424 DOI: 10.1039/c4nr04608k] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Bright emitters with photoluminescence in the spectral region of 800-1600 nm are increasingly important as optical reporters for molecular imaging, sensing, and telecommunication and as active components in electrooptical and photovoltaic devices. Their rational design is directly linked to suitable methods for the characterization of their signal-relevant properties, especially their photoluminescence quantum yield (Φ(f)). Aiming at the development of bright semiconductor nanocrystals with emission >1000 nm, we designed a new NIR/IR integrating sphere setup for the wavelength region of 600-1600 nm. We assessed the performance of this setup by acquiring the corrected emission spectra and Φ(f) of the organic dyes Itrybe, IR140, and IR26 and several infrared (IR)-emissive Cd(1-x)Hg(x)Te and PbS semiconductor nanocrystals and comparing them to data obtained with two independently calibrated fluorescence instruments absolutely or relative to previously evaluated reference dyes. Our results highlight special challenges of photoluminescence studies in the IR ranging from solvent absorption to the lack of spectral and intensity standards together with quantum dot-specific challenges like photobrightening and photodarkening and the size-dependent air stability and photostability of differently sized oleate-capped PbS colloids. These effects can be representative of lead chalcogenides. Moreover, we redetermined the Φ(f) of IR26, the most frequently used IR reference dye, to 1.1 × 10(-3) in 1,2-dichloroethane DCE with a thorough sample reabsorption and solvent absorption correction. Our results indicate the need for a critical reevaluation of Φ(f) values of IR-emissive nanomaterials and offer guidelines for improved Φ(f) measurements.
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54
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Weiß N, Müller-Meskamp L, Selzer F, Bormann L, Eychmüller A, Leo K, Gaponik N. Humidity assisted annealing technique for transparent conductive silver nanowire networks. RSC Adv 2015. [DOI: 10.1039/c5ra01303h] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The capacity of polyvinylpyrrolidone (PVP) to adsorb water vapor was used to decrease the sheet resistance of silver nanowires (AgNW) based electrodes.
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55
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Adam M, Tietze R, Gaponik N, Eychmüller A. QD-Salt Mixed Crystals: the Influence of Salt-Type, Free-Stabilizer, and pH. Z PHYS CHEM 2014. [DOI: 10.1515/zpch-2014-0598] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Colloidal quantum dots (QDs) bear a huge potential in different
application fields due to their unique properties. Unfortunately,
their limited stability against environmental influences and the
limited processability of the colloidal solutions restricts, among
other factors, their widespread implementation. Incorporating the QDs
into an inorganic matrix allows overcoming of these barriers. In this
manuscript, we demonstrate the reproducible incorporation of high
quality CdTe QDs capped with thioglycolic acid into NaCl
and KCl salt crystals. In comparison to previous reports, here
we avoided the production of powder-like, weakly emitting mixed
crystals and/or a loss of large amounts of QDs due to
aggregation. The optimum conditions for this process were found by the
variation of the amount of additional free-stabilizer and the pH of
the saturated salt solutions. Both variables exhibit high influence on
the colloidal stability of the QDs, ensuring the electrostatic forces
on their surface to be high enough to prevent
agglomeration. Incorporation in NaCl as host matrix is
accompanied with pronounced etching of the QDs, causing a blue shift
of the photoluminescence (PL)-spectra upon incorporation while
KCl preserves the original optical properties of the QDs. Under
optimized conditions, even the matrix-induced red shift of the
emission upon incorporation can be overcome, resulting in a higher
predictability of the mixed crystal preparation.
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56
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Zhukovsky SV, Ozel T, Mutlugun E, Gaponik N, Eychmuller A, Lavrinenko AV, Demir HV, Gaponenko SV. Hyperbolic metamaterials based on quantum-dot plasmon-resonator nanocomposites. OPTICS EXPRESS 2014; 22:18290-18298. [PMID: 25089449 DOI: 10.1364/oe.22.018290] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We theoretically demonstrate that nanocomposites made of colloidal semiconductor quantum dot monolayers placed between metal nanoparticle monolayers can function as multilayer hyperbolic metamaterials. Depending on the thickness of the spacer between the quantum dot and nanoparticle layers, the effective permittivity tensor of the nanocomposite is shown to become indefinite, resulting in increased photonic density of states and strong enhancement of quantum dot luminescence. This explains the results of recent experiments [T. Ozel et al., ACS Nano 5, 1328 (2011)] and confirms that hyperbolic metamaterials are capable of increasing the radiative decay rate of emission centers inside them. The proposed theoretical framework can also be used to design quantum-dot/nanoplasmonic composites with optimized luminescence enhancement.
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57
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Zhang X, Marocico CA, Lunz M, Gerard VA, Gun'ko YK, Lesnyak V, Gaponik N, Susha AS, Rogach AL, Bradley AL. Experimental and theoretical investigation of the distance dependence of localized surface plasmon coupled Förster resonance energy transfer. ACS NANO 2014; 8:1273-83. [PMID: 24490807 DOI: 10.1021/nn406530m] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The distance dependence of localized surface plasmon (LSP) coupled Förster resonance energy transfer (FRET) is experimentally and theoretically investigated using a trilayer structure composed of separated monolayers of donor and acceptor quantum dots with an intermediate Au nanoparticle layer. The dependence of the energy transfer efficiency, rate, and characteristic distance, as well as the enhancement of the acceptor emission, on the separations between the three constituent layers is examined. A d(-4) dependence of the energy transfer rate is observed for LSP-coupled FRET between the donor and acceptor planes with the increased energy transfer range described by an enhanced Förster radius. The conventional FRET rate also follows a d(-4) dependence in this geometry. The conditions under which this distance dependence is valid for LSP-coupled FRET are theoretically investigated. The influence of the placement of the intermediate Au NP is investigated, and it is shown that donor-plasmon coupling has a greater influence on the characteristic energy transfer range in this LSP-coupled FRET system. The LSP-enhanced Förster radius is dependent on the Au nanoparticle concentration. The potential to tune the characteristic energy transfer distance has implications for applications in nanophotonic devices or sensors.
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58
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Dubavik A, Lesnyak V, Gaponik N, Eychmüller A. A Versatile Approach for a Variety of Amphiphilic Nanoparticles: Semiconductor – Plasmonic – Magnetic. Z PHYS CHEM 2014. [DOI: 10.1515/zpch-2014-0474] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
In this work we summarize last achievements of the colloidal synthesis
and applications of different amphiphilic nanoparticles, among which
are semiconductor, metal and metal oxide materials. All these
nanoparticles have been obtained employing polyethylene glycol based
stabilizers which provide compatibility with a wide variety of media
from nonpolar organics to water. Owing to their versatile solubility,
the materials obtained have the ability of spontaneous multiphase
transfer. Moreover, they have been shown to permeate through cell
membranes avoiding endocytosis which makes them particularly
interesting for bio-applications.
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59
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Melnikau D, Savateeva D, Lesnyak V, Gaponik N, Fernández YN, Vasilevskiy MI, Costa MF, Mochalov KE, Oleinikov V, Rakovich YP. Resonance energy transfer in self-organized organic/inorganic dendrite structures. NANOSCALE 2013; 5:9317-9323. [PMID: 23949098 DOI: 10.1039/c3nr03016d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Hybrid materials formed by semiconductor quantum dots and J-aggregates of cyanine dyes provide a unique combination of enhanced absorption in inorganic constituents with large oscillator strength and extremely narrow exciton bands of the organic component. The optical properties of dendrite structures with fractal dimension 1.7-1.8, formed from J-aggregates integrated with CdTe quantum dots (QDs), have been investigated by photoluminescence spectroscopy and fluorescence lifetime imaging microscopy. Our results demonstrate that (i) J-aggregates are coupled to QDs by Förster-type resonant energy transfer and (ii) there are energy fluxes from the periphery to the centre of the structure, where the QD density is higher than in the periphery of the dendrite. Such an anisotropic energy transport can be only observed when dendrites are formed from QDs integrated with J-aggregates. These QD/J-aggregate hybrid systems can have applications in light harvesting systems and optical sensors with extended absorption spectra.
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60
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Lesnyak V, Gaponik N, Eychmüller A. Colloidal semiconductor nanocrystals: the aqueous approach. Chem Soc Rev 2013; 42:2905-29. [PMID: 23165911 DOI: 10.1039/c2cs35285k] [Citation(s) in RCA: 224] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
This article summarizes the main achievements and challenges in the field of the aqueous synthesis of semiconductor quantum dots in colloidal solutions. Developments in the last two decades demonstrate the great potential of this approach to synthesize nanocrystalline materials with superior properties such as strong photoluminescence, long time stability and compatibility with biological media, and the variability in assembling and self-assembling into larger structures or on surfaces. Being relatively straightforward, the aqueous approach provides some advantages such as versatility, scalability, environmental friendliness and cost effectiveness, leading in summary to very attractive application perspectives.
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61
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Seker UOS, Mutlugun E, Hernandez-Martinez PL, Sharma VK, Lesnyak V, Gaponik N, Eychmüller A, Demir HV. Bio-nanohybrids of quantum dots and photoproteins facilitating strong nonradiative energy transfer. NANOSCALE 2013; 5:7034-7040. [PMID: 23803876 DOI: 10.1039/c3nr01417g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Utilization of light is crucial for the life cycle of many organisms. Also, many organisms can create light by utilizing chemical energy emerged from biochemical reactions. Being the most important structural units of the organisms, proteins play a vital role in the formation of light in the form of bioluminescence. Such photoproteins have been isolated and identified for a long time; the exact mechanism of their bioluminescence is well established. Here we show a biomimetic approach to build a photoprotein based excitonic nanoassembly model system using colloidal quantum dots (QDs) for a new bioluminescent couple to be utilized in biotechnological and photonic applications. We concentrated on the formation mechanism of nanohybrids using a kinetic and thermodynamic approach. Finally we propose a biosensing scheme with an ON/OFF switch using the QD-GFP hybrid. The QD-GFP hybrid system promises strong exciton-exciton coupling between the protein and the quantum dot at a high efficiency level, possessing enhanced capabilities of light harvesting, which may bring new technological opportunities to mimic biophotonic events.
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62
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Liu W, Rodriguez P, Borchardt L, Foelske A, Yuan J, Herrmann AK, Geiger D, Zheng Z, Kaskel S, Gaponik N, Kötz R, Schmidt TJ, Eychmüller A. Bimetall-Aerogele: hoch effiziente Elektrokatalysatoren für die Sauerstoffreduktion. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201303109] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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63
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Liu W, Rodriguez P, Borchardt L, Foelske A, Yuan J, Herrmann AK, Geiger D, Zheng Z, Kaskel S, Gaponik N, Kötz R, Schmidt TJ, Eychmüller A. Bimetallic Aerogels: High-Performance Electrocatalysts for the Oxygen Reduction Reaction. Angew Chem Int Ed Engl 2013; 52:9849-52. [DOI: 10.1002/anie.201303109] [Citation(s) in RCA: 221] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Indexed: 11/10/2022]
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64
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Mundra P, Otto T, Gaponik N, Eychmüller A. Automated setup for spray assisted layer-by-layer deposition. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:074101. [PMID: 23902085 DOI: 10.1063/1.4811662] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The design for a setup allowing the layer-by-layer (LbL) assembly of thin films consisting of various colloidal materials is presented. The proposed system utilizes the spray-assisted LbL approach and is capable of autonomously producing films. It provides advantages to existing LbL procedures in terms of process speed and applicability. The setup offers several features that are advantageous for routine operation like an actuated sample holder, stainless steel spraying nozzles, or an optical liquid detection system. The applicability is demonstrated by the preparation of films containing semiconductor nanoparticles, namely, CdSe∕CdS quantum dots and a polyelectolyte. The films of this type are of potential interest for applications in optoelectronic devices such as light-emitting diodes or solar cells.
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65
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Rakovich A, Nabiev I, Sukhanova A, Lesnyak V, Gaponik N, Rakovich YP, Donegan JF. Large enhancement of nonlinear optical response in a hybrid nanobiomaterial consisting of bacteriorhodopsin and cadmium telluride quantum dots. ACS NANO 2013; 7:2154-2160. [PMID: 23448202 DOI: 10.1021/nn3049939] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We report wavelength-dependent enormous enhancement of the nonlinear refractive index of wild-type bacteriorhodopsin in the presence of semiconductor quantum dots. The effect is strongest in the region just below the absorption edge of both constituents of this hybrid material and in samples that show strong Förster resonance energy transfer. We show that enhancements of up to 4000% can be achieved by controlled engineering of the hybrid structure involving variations of the molar ratio of the constituents. This new hybrid material with exceptional nonlinear properties will have numerous photonic and optoelectronic applications employing its photochromic, energy transfer, and conversion properties.
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66
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Leubner S, Hatami S, Esendemir N, Lorenz T, Joswig JO, Lesnyak V, Recknagel S, Gaponik N, Resch-Genger U, Eychmüller A. Experimental and theoretical investigations of the ligand structure of water-soluble CdTe nanocrystals. Dalton Trans 2013; 42:12733-40. [DOI: 10.1039/c3dt50802a] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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67
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Yuan J, Wen D, Gaponik N, Eychmüller A. Enzyme-Encapsulating Quantum Dot Hydrogels and Xerogels as Biosensors: Multifunctional Platforms for Both Biocatalysis and Fluorescent Probing. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201205791] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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68
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Yuan J, Wen D, Gaponik N, Eychmüller A. Enzyme-Encapsulating Quantum Dot Hydrogels and Xerogels as Biosensors: Multifunctional Platforms for Both Biocatalysis and Fluorescent Probing. Angew Chem Int Ed Engl 2012; 52:976-9. [DOI: 10.1002/anie.201205791] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Revised: 11/06/2012] [Indexed: 12/21/2022]
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69
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Zhang X, Marocico CA, Lunz M, Gerard VA, Gun'ko YK, Lesnyak V, Gaponik N, Susha AS, Rogach AL, Bradley AL. Wavelength, concentration, and distance dependence of nonradiative energy transfer to a plane of gold nanoparticles. ACS NANO 2012; 6:9283-9290. [PMID: 22973978 DOI: 10.1021/nn303756a] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Nonradiative energy transfer to metal nanoparticles is a technique used for optical-based distance measurements which is often implemented in sensing. Both Förster resonant energy transfer (FRET) and nanometal surface energy transfer (NSET) mechanisms have been proposed for emission quenching in proximity to metal nanoparticles. Here quenching of emission of colloidal quantum dots in proximity to a monolayer of gold nanoparticles is investigated. Five differently sized CdTe quantum dots are used to probe the wavelength dependence of the quenching mechanism as their emission peak moves from on resonance to off resonance with respect to the localized surface plasmon peak of the gold nanoparticle layer. The gold nanoparticle concentration and distance dependences of energy transfer are discussed. Photoluminescence quenching and lifetime data are analyzed using both FRET and NSET models and the extracted characteristic distances are compared with theory. Good agreement with FRET theory has been found for quantum dots with emission close to the localized surface plasmon resonance, though larger than expected Förster radii are observed for quantum dots with emission red-shifted with respect to the localized surface plasmon peak. Closer agreement between experimental and theoretical characteristic distances can be found across the full wavelength range within a NSET approach.
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70
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Otto T, Müller M, Mundra P, Lesnyak V, Demir HV, Gaponik N, Eychmüller A. Colloidal nanocrystals embedded in macrocrystals: robustness, photostability, and color purity. NANO LETTERS 2012; 12:5348-54. [PMID: 22978450 DOI: 10.1021/nl3027444] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The incorporation of colloidal quantum dots (QDs) into ionic crystals of various salts (NaCl, KCl, KBr, etc.) is demonstrated. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Moreover, the ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment and as a result providing them with extraordinary high photo- and chemical stability. A prototype of a white light-emitting diode (WLED) with a color conversion layer consisting of this kind of mixed crystals is demonstrated. These materials may also find applications in nonlinear optics and as luminescence standards.
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71
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Wolf A, Lesnyak V, Gaponik N, Eychmüller A. Quantum-Dot-Based (Aero)gels: Control of the Optical Properties. J Phys Chem Lett 2012; 3:2188-93. [PMID: 26295769 DOI: 10.1021/jz300726n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
In this work, we have developed novel hybrid quantum dot gels based on the controllable and reversible assembly of nanoparticles via metal-tetrazole complexation. Combining in one hybrid network nanocrystals of different semiconductors (ZnSe and CdTe) as well as quantum dots of different sizes (green and red emitting CdTe) with different band gaps, we have examined energy relations within these systems and act out a facile route to the color design of the resulting gels. Efficient energy pumping from donor quantum dots to acceptors leads to a remarkable enhancement of the emission intensity of the gel. Furthermore, by integrating three different quantum dot types into one network, we obtained a white-light-emitting aerogel.
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72
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Mutlugun E, Hernandez-Martinez PL, Eroglu C, Coskun Y, Erdem T, Sharma VK, Unal E, Panda SK, Hickey SG, Gaponik N, Eychmüller A, Demir HV. Large-area (over 50 cm × 50 cm) freestanding films of colloidal InP/ZnS quantum dots. NANO LETTERS 2012; 12:3986-93. [PMID: 22783904 DOI: 10.1021/nl301198k] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We propose and demonstrate the fabrication of flexible, freestanding films of InP/ZnS quantum dots (QDs) using fatty acid ligands across very large areas (greater than 50 cm × 50 cm), which have been developed for remote phosphor applications in solid-state lighting. Embedded in a poly(methyl methacrylate) matrix, although the formation of stand-alone films using other QDs commonly capped with trioctylphosphine oxide (TOPO) and oleic acid is not efficient, employing myristic acid as ligand in the synthesis of these QDs, which imparts a strongly hydrophobic character to the thin film, enables film formation and ease of removal even on surprisingly large areas, thereby avoiding the need for ligand exchange. When pumped by a blue LED, these Cd-free QD films allow for high color rendering, warm white light generation with a color rendering index of 89.30 and a correlated color temperature of 2298 K. In the composite film, the temperature-dependent emission kinetics and energy transfer dynamics among different-sized InP/ZnS QDs are investigated and a model is proposed. High levels of energy transfer efficiency (up to 80%) and strong donor lifetime modification (from 18 to 4 ns) are achieved. The suppression of the nonradiative channels is observed when the hybrid film is cooled to cryogenic temperatures. The lifetime changes of the donor and acceptor InP/ZnS QDs in the film as a result of the energy transfer are explained well by our theoretical model based on the exciton-exciton interactions among the dots and are in excellent agreement with the experimental results. The understanding of these excitonic interactions is essential to facilitate improvements in the fabrication of photometrically high quality nanophosphors. The ability to make such large-area, flexible, freestanding Cd-free QD films pave the way for environmentally friendly phosphor applications including flexible, surface-emitting light engines.
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73
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Yuan J, Gaponik N, Eychmüller A. Application of Polymer Quantum Dot-Enzyme Hybrids in the Biosensor Development and Test Paper Fabrication. Anal Chem 2012; 84:5047-52. [DOI: 10.1021/ac300714j] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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74
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Otto T, Mundra P, Schelter M, Frolova E, Dorfs D, Gaponik N, Eychmüller A. Application Prospects of Spray-Assisted Layer-by-Layer Assembly of Colloidal Nanoparticles. Chemphyschem 2012; 13:2128-32. [DOI: 10.1002/cphc.201200210] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Indexed: 11/11/2022]
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75
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Jiang P, Schroeder T, Bath M, Lesnyak V, Gaponik N, Eychmüller A, Benson O. Incoherent photon conversion in selectively infiltrated hollow-core photonic crystal fibers for single photon generation in the near infrared. OPTICS EXPRESS 2012; 20:11536-11547. [PMID: 22565773 DOI: 10.1364/oe.20.011536] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
At present, there exist a number of on-demand single photon sources with high emission rates and stability even at room temperature. However, their emission wavelength is restricted to specific transitions in single quantum emitters. Single photon generation in the near infrared, possibly within the telecom band, though most urgently needed, is particularly crucial. In this paper, we suggest an experimental method to convert visible single photons from a defect center in diamond to the near infrared. The conversion relies on efficient absorption by colloidal quantum dots and subsequent Stokes-shifted emission. The desired target wavelength can be chosen almost arbitrarily by selecting quantum dots with a suitable emission spectrum. A hollow core photonic crystal fiber selectively filled with a solution of quantum dots was used to achieve at the same time a single photon absorption probability of near unity and a very high re-collection efficiency of Stokes-shifted fluorescence (theoretically estimated to be 26%). A total conversion efficiency of light of 0.1% is achieved. Experimental strategies to significantly enhance this number are presented.
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