Debye Institute for Nanomaterials Science

Utrecht, Netherlands

Debye Institute for Nanomaterials Science

Utrecht, Netherlands
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Rabouw F.T.,Debye Institute for Nanomaterials Science | Lunnemann P.,FOM Institute for Atomic and Molecular Physics | Lunnemann P.,Technical University of Denmark | Van Dijk-Moes R.J.A.,Debye Institute for Nanomaterials Science | And 5 more authors.
Nano Letters | Year: 2013

Progress to reduce nonradiative Auger decay in colloidal nanocrystals has recently been made by growing thick shells. However, the physics of Auger suppression is not yet fully understood. Here, we examine the dynamics and spectral characteristics of single CdSe-dot-in-CdS-rod nanocrystals. These exhibit blinking due to charging/discharging, as well as trap-related blinking. We show that one-dimensional electron delocalization into the rod-shaped shell can be as effective as a thick spherical shell at reducing Auger recombination of the negative trion state. © 2013 American Chemical Society.

News Article | September 12, 2016

Fig. Visualisation of disorder-confined light in a photonic crystal. The green membrane is a photonic crystal with a waveguide; the patterns on top of it indicate the light signal that is stored. Credit: Utrecht University Faculty of Science Researchers at the Debye Institute for Nanomaterials Science, together with colleagues from the University of Twente and Thales Research and Technology (France), have found a non-invasive technique to measure the intensity profile of light that is confined by disorder in nano-sized photonic devices. This method may eventually lead to faster optical communications, and faster processing in quantum information technologies. The researchers published their results in the leading optical journal Optics Express on 12 September 2016. Every nanostructure suffers from unavoidable disorder: a disturbance of its function caused by unavoidable irregularities in nanofabrication. Contrary to what the name might suggest, disorder in a nanostructure is not necessarily a disadvantage. Disorder can cause light to be tightly confined, and if its intensity profile is measured accurately, the confined light might be used to make components for quantum information technology and high speed optical communication. One bottleneck in high-speed optical communication is that light signals have to be converted to electronic signals at nodes to switch data to different destinations. This conversion can be avoided with the help of optical buffers that store light signals temporarily. Right now, these buffers are usually implemented with optical fibres that are several centimeters long, which can store light for a few nanoseconds. However, with smart use of disorder-induced confinement, nanophotonic circuits 100 times smaller – only one-tenth of a millimeter long – can store light for a similar time. Photonic crystal waveguides are nanophotonic structures in which light confinement by disorder widely occurs. In order to make use of the confined light, the first essential step is to identify where the light is confined and what its spatial profile is. Compared to the previous measuring methods, which perturb the structure, Jin Lian (Debye Institute) and his colleagues have developed a new non-invasive method to precisely identify the spatial and spectral information, using local heating. The researchers used a blue laser to slightly heat a small spot on the crystal. The response of the optical system reveals how much light is confined there. Explore further: Unavoidable disorder used to build nanolaser More information: Measurement of the profiles of disorder-induced localized resonances in photonic crystal waveguides by local tuning,

Rabouw F.T.,Debye Institute for Nanomaterials Science | Meijerink A.,Debye Institute for Nanomaterials Science
Journal of Physical Chemistry C | Year: 2015

Cooperative energy transfer (ET) is a quantum cutting (or downconversion) process where a luminescent center splits its excited state energy in two by simultaneous transfer to two nearby acceptor centers, thus yielding two low-energy photons for each high-energy photon absorbed. It has the potential to greatly enhance the efficiency of phosphors for lighting or the UV/blue response of next generation photovoltaics. Many pairs of luminescent centers have been claimed to enable quantum cutting by cooperative ET. However, direct proof that the ET mechanism is cooperative is often lacking. Here we present a model that can be used to fit or predict the dynamics of cooperative ET in codoped crystals, as a function of the concentration of acceptor centers. It also yields an analytical expression for the efficiency of cooperative ET. Our model can be used to provide evidence for quantum cutting materials, quantify the ET parameter(s), and optimize the doping concentration. © 2015 American Chemical Society.

Versteegh M.A.M.,University Utrecht | Versteegh M.A.M.,Debye Institute for Nanomaterials Science | Dieks D.,University Utrecht
American Journal of Physics | Year: 2011

Identical classical particles are distinguishable. This distinguishability affects the number of ways W a macrostate can be realized on the microlevel, and from the relation S=k ln W leads to a nonextensive expression for the entropy. This result is usually considered incorrect because of its inconsistency with thermodynamics. It is sometimes concluded from this inconsistency that identical particles are fundamentally indistinguishable and that quantum mechanics is indispensable for making sense of this inconsistency. In contrast, we argue that the classical statistics of distinguishable particles and the resulting nonextensive entropy function are perfectly acceptable from both a theoretical and an experimental perspective. The inconsistency with thermodynamics can be removed by taking into account that the entropy concept in statistical mechanics is not completely identical to the thermodynamical one. We observe that even identical quantum particles are in some cases distinguishable, and conclude that quantum mechanics is irrelevant to the Gibbs paradox. © 2011 American Association of Physics Teachers.

Pietra F.,Debye Institute for Nanomaterials Science | Van Dijk - Moes R.J.A.,Debye Institute for Nanomaterials Science | Ke X.,University of Antwerp | Bals S.,University of Antwerp | And 3 more authors.
Chemistry of Materials | Year: 2013

CdSe(core)/CdS(shell) nanorods (NRs) have been extensively investigated for their unique optical properties, such as high photoluminescence (PL) quantum efficiency (QE) and polarized light emission. The incorporation of these NRs in silica (SiO2) is of high interest, since this renders them processable in polar solvents while increasing their photochemical stability, which would be beneficial for their application in LEDs and as biolabels. We report the synthesis of highly luminescent silica-coated CdSe/CdS NRs, by using the reverse micelle method. The mechanism for the encapsulation of the NRs in silica is unravelled and shown to be strongly influenced by the NR shape and its asymmetry. This is attributed to both the different morphology and the different crystallographic nature of the facets terminating the opposite tips of the NRs. These results lead to the formation of a novel class of NR architectures, whose symmetry can be controlled by tuning the degree of coverage of the silica shell. Interestingly, the encapsulation of the NRs in silica leads to a remarkable increase in their photostability, while preserving their optical properties. © 2013 American Chemical Society.

Pietra F.,Debye Institute for Nanomaterials Science | Rabouw F.T.,Debye Institute for Nanomaterials Science | Evers W.H.,Debye Institute for Nanomaterials Science | Byelov D.V.,Debye Institute for Nanomaterials Science | And 3 more authors.
Nano Letters | Year: 2012

We study the self-assembly of colloidal CdSe/CdS nanorods (NRs) at the liquid/air interface combining time-resolved in situ grazing-incidence small angle X-ray scattering (GISAXS) and ex situ transmission electron microscopy (TEM). Our study shows that NR superstructure formation occurs at the liquid/air interface. Short NRs self-assemble into micrometers long tracks of NRs lying side by side flat on the surface. In contrast, longer NRs align vertically into ordered superstructures. Systematic variation of the NR length and initial concentration of the NR dispersion allowed us to tune the orientation of the NRs in the final superstructure. With GISAXS, we were able to follow the dynamics of the self-assembly. We propose a model of hierarchical self-organization that provides a basis for the understanding of the length-dependent self-organization of NRs at the liquid/air interface. This opens the way to new materials based on NR membranes and anisotropic thin films. © 2012 American Chemical Society.

Lunnemann P.,FOM Institute for Atomic and Molecular Physics | Lunnemann P.,Technical University of Denmark | Rabouw F.T.,Debye Institute for Nanomaterials Science | Van Dijk-Moes R.J.A.,Debye Institute for Nanomaterials Science | And 3 more authors.
ACS Nano | Year: 2013

We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage's method that uses nanometer-controlled optical mode density variations near a mirror, not only allows an extraction of calibrated ensemble-averaged rates, but for the first time also to quantify the full inhomogeneous dispersion of radiative and non radiative decay rates across thousands of nanocrystals. We apply the technique to novel ultrastable CdSe/CdS dot-in-rod emitters. The emitters are of large current interest due to their improved stability and reduced blinking. We retrieve a room-temperature ensemble average quantum efficiency of 0.87 ± 0.08 at a mean lifetime around 20 ns. We confirm a log-normal distribution of decay rates as often assumed in literature, and we show that the rate distribution-width, that amounts to about 30% of the mean decay rate, is strongly dependent on the local density of optical states. © 2013 American Chemical Society.

Beale A.M.,Debye Institute for NanoMaterials Science | Jacques S.D.M.,Debye Institute for NanoMaterials Science | Weckhuysen B.M.,Debye Institute for NanoMaterials Science
Chemical Society Reviews | Year: 2010

Heterogeneous catalysis is a term normally used to describe a group of catalytic processes, yet it could equally be employed to describe the catalytic solid itself. A better understanding of the chemical and structural variation within such materials is thus a pre-requisite for the rationalising of structure-function relationships and ultimately to the design of new, more sustainable catalytic processes. The past 20 years has witnessed marked improvements in technologies required for analytical measurements at synchrotron sources, including higher photon brightness, nano-focusing, rapid, high resolution data acquisition and in the handling of large volumes of data. It is now possible to image materials using the entire synchrotron radiative profile, thus heralding a new era of in situ/operando measurements of catalytic solids. In this tutorial review we discuss the recent work in this exciting new research area and finally conclude with a future outlook on what will be possible/challenging to measure in the not-too-distant future. © 2010 The Royal Society of Chemistry.

Granados Del Aguila A.,Radboud University Nijmegen | Jha B.,Radboud University Nijmegen | Pietra F.,Debye Institute for Nanomaterials Science | Groeneveld E.,Debye Institute for Nanomaterials Science | And 4 more authors.
ACS Nano | Year: 2014

Light emission of semiconductor nanocrystals is a complex process, depending on many factors, among which are the quantum mechanical size confinement of excitons (coupled electron-hole pairs) and the influence of confined phonon modes and the nanocrystal surface. Despite years of research, the nature of nanocrystal emission at low temperatures is still under debate. Here we unravel the different optical recombination pathways of CdSe/CdS dot-in-rod systems that show an unprecedented number of narrow emission lines upon resonant laser excitation. By using self-assembled, vertically aligned rods and application of crystallographically oriented high magnetic fields, the origin of all these peaks is established. We observe a clear signature of an acoustic-phonon assisted transition, separated from the zero-phonon emission and optical-phonon replica, proving that nanocrystal light emission results from an intricate interplay between bright (optically allowed) and dark (optically forbidden) exciton states, coupled to both acoustic and optical phonon modes. © 2014 American Chemical Society.

News Article | November 8, 2016

By sending light through a material several times, it is possible to find a path through which much more light can pass through the material. The researchers then measure the amount of light that makes it through this path at different wavelengths. Credit: Utrecht University Faculty of Science Shining a light through opaque materials seems impossible. And yet, researchers at the Debye Institute for Nanomaterials Science (Utrecht University) and the University of Twente have managed to increase the transmission of light through an opaque material by shining it along special paths. This could lead to a better understanding of the transport of light through materials such as skin. The researchers published their results in the prestigious journal Optics Express on 7 November, 2016. Light diffusion is a phenomenon that occurs when light waves come into contact with an uneven surface or in an object with an inhomogeneous structure. This diffusion makes it impossible to see through skin, paper or clouds, for example. These materials are largely opaque, and only a small percentage of the light can penetrate through them. And yet these materials do have open channels, special paths through the material that the light waves can follow, no matter how thick the material is. Utrecht Ph.D. student Jeroen Bosch has located these open channels to send much more light through an opaque material. In order to discover precisely how the light should be projected on the material, the researchers "played ping pong" with the light. "We send the light through the material in a random manner, and then we use data about the scattering of the light to send it along the same path in a slightly different manner," Bosch explains. "That way, more light passes through the material." By repeating the process several times – sending the light back and forth through the material – the researchers discovered what shape the light wave must have in order to make its way through the material. All colours are different The shape of the wave front – the front edge of the light wave – determines the degree to which the light can penetrate through the material. And the optimal shape of the wave front is different for every colour of light. "The principle works for all wavelengths, but for each wavelength, there is only a single shape of wave front that works," says Bosch. "If you fix the shape of the wave front and then change the wavelength, you see that less and less light penetrates through the material." This knowledge of wavelength dependency of open channels provides the researchers with a measurement for the 'path length' of these open channels. How long does the light travel along such a special path? The answer to this question provides insight into the transport of light through diffusive materials, which is extremely useful for looking into and through such materials. More information: Jeroen Bosch et al. Frequency width of open channels in multiple scattering media, Optics Express (2016). DOI: 10.1364/OE.24.026472

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