Search

A major goal of in vivo imaging is to obtain individualized structural, functional, and molecular information to provide personalized medicine. In particular, optical imaging uses non-ionizing radiation to provide functional information such as hemoglobin concentration and also visualize exogenous contrast agents as well as molecular and functional markers. Indeed, in vivo optical imaging extends across a wide range of applications, from cellular to organ levels. At high end of the spectrum, diffuse optical tomography (DOT) can penetrate up to 10 centimeters but only offer low-resolution images (> 5mm) due to highly scattering nature of the tissue. Significant effort has been spent on multi-modality imaging techniques to improve the resolution of DOT. While combining DOT with spatial information defined by a separate anatomical imaging modality is promising, there are many challenges and inaccuracies that arise with co-registration. However this can be overcome with a novel multi-modality imaging technique, Photo-Magnetic Imaging (PMI) which uses MRI as a detector to provide both high resolution anatomical and optical information. PMI takes advantage of the 3D measurement capabilities of MR thermometry (MRT) to non-invasively measure the temperature increase of the medium induced by a laser to acquire a temperature map of the entire volume. As DOT measures the photon flux only from the boundary, the major advantage of PMI is that high absorbing regions can be resolved directly from the high spatial resolution temperature map. These measurements can then be converted to obtain the optical absorption properties of the tissue using a reconstruction algorithm to model the light propagation and heat transfer in tissue. This thesis will present the development of the first preclinical in vivo small animal PMI system prototype using the safety standards set by the American National Standard Institution. To optimize the system for in vivo studies, a fast PMI reconstruction method was also developed to accelerate the original PMI reconstruction method ~1000 times faster. These promising results validated the practicality of PMI for preclinical studies and showed the potential of PMI for clinical studies. This led to the development of the first human PMI prototype for clinical breast studies.

Accomplishing equilibrium in terms of transfer efficiency for dual-band wireless energy transfer (WET) system remains as one of key concerns particularly in the implementation of a single transmitter device which supports simultaneous energy and data transfer functionality. Three stages of design method are discussed in addressing the aforementioned concern. A single layer dual-band printed spiral resonator for non-radiative wireless energy transfer operating at 6.78 MHz and 13.56 MHz is presented. By employing multi-coil approach, measured power transfer efficiency for a symmetrical link separated at axial distance of 30 mm are 72.34% and 74.02% at the respective frequency bands. When operating distance is varied between 30 mm to 38 mm, consistency of simulated peak transfer efficiency above 50% is achievable.

Here we designed and synthesized CdSe/CdSe1-xTex core/crown nanoplatelets (NPLs) with controlled crown compositions by using the core-seeded-growth approach. We confirmed the uniform growth of the crown regions with well-defined shape and compositions by employing transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. By precisely tuning the composition of the CdSe1-xTex crown region from pure CdTe (x = 1.00) to almost pure CdSe doped with several Te atoms (x = 0.02), we achieved tunable excitonic properties without changing the thickness of the NPLs and demonstrated the evolution of type-II electronic structure. Upon increasing the Te concentration in the crown region, we obtained continuously tunable photoluminescence peaks within the range of ∼570 nm (for CdSe1-xTex crown with x = 0.02) and ∼660 nm (for CdSe1-xTex crown with x = 1.00). Furthermore, with the formation of the CdSe1-xTex crown region, we observed substantially improved photoluminescence quantum yields (up to ∼95%) owing to the suppression of nonradiative hole trap sites. Also, we found significantly increased fluorescence lifetimes from ∼49 up to ∼326 ns with increasing Te content in the crown, suggesting the transition from quasi-type-II to type-II electronic structure. With their tunable excitonic properties, this novel material presented here will find ubiquitous use in various efficient light-emitting and -harvesting applications. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Accepted version The authors gratefully acknowledge the financial support from Singapore National Research Foundation under the programs of NRF-NRFI2016-08 and NRF-CRP-6-2010-02 and the Science and Engineering Research Council, Agency for Science, Technology and Research (A*STAR) of Singapore; EU-FP7 Nanophotonics4Energy NoE; and TUBITAK EEEAG 114E449 and 114F326. H.V.D. acknowledges support from ESF-EURYI and TUBAGEBIP. Y.K., O.E., and T.E. acknowledge support from TUBITAK BIDEB.

The presence of an excitonic element in close proximity of a plasmonic nanostructure, under certain conditions, may lead to a nonradiative resonant energy transfer known as Exciton Plasmon Resonant Energy Transfer (EPRET) process. The exciton-plasmon coupling and dynamics have been intensely studied in the last decade; still many relevant aspects need more in-depth studies. Understanding such phenomenon is not only important from fundamental viewpoint, but also essential to unlock many promising applications. In this review we investigate the plasmon-exciton resonant energy transfer in different hybrid systems at the nano- and mesoscales, in order to gain further understanding of such processes across scales and pave the way towards active plasmonic devices.

The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law., We thank the EPSRC (EP/H040218 and EP/I019278) for financial support.

Recent studies show that the spectral behaviour of localized surface plasmon resonances (LPSRs) in metallic nanoparticles su er from both a redshift and a broadening in the transition from the far- to the near-field regimes. An interpretation of this efect was given in terms of the evanescent and propagating components of the angular spectrum representation of the radiated eld. Due to the increasing interest awakened by magnetodielectric materials as a both low-loss material option for nanotechnology applications, and also for their particular scattering properties, here we study the spectral response of a magnetodielectric nanoparticle as a basic element of a dielectric nano-antenna. This study is made by analyzing the changes su ered by the scattered electromagnetic field when propagating from the surface of this dielectric nanostructure to the far-zone in terms of propagating and evanescent plane wave components of the radiated fields. This research was supported by MICINN (Spanish Ministry of Science and Innovation) with project FIS2013- 45854-P.

An all-solution processed and all-colloidal laser is demonstrated using tailored CdSe/CdS core/shell quantum dots, which exhibit highly stable and low-threshold optical gain owing to substantially suppressed non-radiative Auger recombination. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Plasmonics exhibits the potential to break the diffraction limit and bridge the gap between electronics and photonics by routing and manipulating light at the nanoscale. However, the inherent and strong energy dissipation present in metals, especially in the near-infrared and visible wavelength ranges, significantly hampers the applications in nanophotonics. Therefore, it is a major challenge to mitigate the losses. One way to compensate the losses is to incorporate gain media into plasmonics. Here, we experimentally show that the incorporation of gain material into a local surface plasmonic system (Au/silica/silica dye core-multishell nanoparticles) leads to a resonant energy transfer from the gain media to the plasmon. The optimized conditions for the largest loss compensation are reported. Both the coupling distance and the spectral overlap are the key factors to determine the resulting energy transfer. The interplay of these factors leads to a non-monotonous photoluminescence dependence as a function of the silica spacer shell thickness. Nonradiative transfer rate is increased by more than 3 orders of magnitude at the resonant condition, which is key evidence of the strongest coupling occurring between the plasmon and the gain material. © 2012 American Chemical Society.

Supporting Information: The details of preparation of peptide, buffer solutions, and nanocrystals, layer-by-layer assembly, isothermal titration calorimetry, circular dichroism spectroscopy, quartz crystal microbalance, atomic force microscopy, and time-resolved photoluminescence studies, and protease digestion and control experiments. A bottom-up approach for constructing colloidal semiconductor quantum dot (QDot) nanocomposites that facilitate nonradiative Förster-type resonance energy transfer (FRET) using polyelectrolyte peptides was proposed and realized. The electrostatic interaction of these polypeptides with altering chain lengths was probed for thermodynamic, structural, and morphological aspects. The resulting nanocomposite film was successfully cut with the protease by digesting the biomimetic peptide layer upon which the QDot assembly was constructed. The ability to control photoluminescence decay lifetime was demonstrated by proteolytic enzyme activity, opening up new possibilities for biosensor applications.

Cataloged from PDF version of article. his work demonstrates the comparative studies of non-radiative resonance energy transfer in bi-polymer nanoparticles based on fluorescent conjugated polymers. For this purpose, poly[(9,9-dihexylfluorene) (PF) as a donor (D) and poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) as an acceptor (A) have been utilized, from which four different bi-polymer nanoparticle systems are designed and synthesized. Both, steady-state fluorescence spectra and time-resolved fluorescence measurements indicate varying energy transfer efficiencies from the host polymer PF to the acceptor polymer MEH-PPV depending on the D-A distances and structural properties of the nanoparticles. The first approach involves the preparation of PF and MEH-PPV nanoparticles separately and mixing them at a certain ratio. In the second approach, first PF and MEH-PPV solutions are mixed prior to nanoparticle formation and then nanoparticles are prepared from the mixture. Third and fourth approaches involve the sequential nanoparticle preparation. In the former, nanoparticles are prepared to have PF as a core and MEH-PPV as a shell. The latter is the reverse of the third in which the core is MEH-PPV and the shell is PF. The highest energy transfer efficiency recorded to be 35% is obtained from the last system, in which a PF layer is sequentially formed on MEH-PPV NPs. © 2010 Optical Society of America.

The dynamics of aggregation between electrostatically bound carboxylate and amine terminated poly(amidoamine) {PAMAM} dendrimers have been investigated in aqueous medium. Unlike the covalently connected tecto (dendrimer) analogues, aggregates of electrostatically bound PAMAM dendrimers can self-assemble in a dendritic pattern, generating fascinating fractal structures. The kinetic studies of the aggregation in water by dynamic light scattering (DLS) experiments suggest that diffusion limited colloidal aggregation (DLCA) is the prevailing mechanism for the fractal growth between 3.5 generation carboxylate terminated PAMAM dendrimer and fourth generation amine terminated PAMAM dendrimer. The fractal aggregation observed in aqueous medium was further corroborated by scanning and transmission electron microscopic studies. Furthermore, unprecedented enhancement in the intrinsic emission intensity from PAMAM dendrimer was observed associated with the dendritic aggregation of the dendrimer units. Most importantly, the present study suggests that electrostatic self-assembly can be utilized as an effective synthetic strategy to generate highly stable, nano-to microscale higher order complex structures from PAMAM dendrimers, which significantly reduces the nonradiative pathways of the excitons, resulting in many fold enhancements in the intrinsic emission intensity from the system. � 2010 American Chemical Society.

We propose and demonstrate highly efficient nonradiative Foumlrster resonance energy transfer (FRET) facilitated by the use of positively charged CdSe/ZnS core-shell nanocrystals (NCs) for light-harvesting in solution. With rhodamine B dye molecules used as the acceptors, our time-resolved photoluminescence measurements show substantial lifetime modifications of these amine-functionalized NC donors from 18.16 to 1.88 ns with FRET efficiencies >90% in solution. These strong modifications allow for light-harvesting beyond the absorption spectral range of the acceptor dye molecules.

We proposed and demonstrated architectural tuning of color chromaticity by controlling photoluminescence decay kinetics through nonradiative Förster resonance energy transfer in the heterostructure of layer-by-layer spaced CdTe nanocrystal (NC) solids. We achieved highly sensitive tuning by precisely adjusting the energy transfer efficiency from donor NCs to acceptor NCs via controlling interspacing between them at the nanoscale. By modifying decay lifetimes of donors from 12.05 to 2.96 ns and acceptors from 3.68 to 14.57 ns, we fine-tuned chromaticity coordinates from (x,y) = (0.575,0.424) to (0.632, 0.367). This structural adjustment enabled a postsynthesis color tuning capability, alternative or additive to using the size, shape, and composition of NCs. © 2009 American Institute of Physics.

Conference name: Conference on Lasers and Electro-Optics 2009 Date of Conference: 31 May–5 June 2009 We present white light generating nonradiative Förster resonance energy transfer at a rate of (2ns)-1 directly from epitaxial InGaN/GaN quantum wells to CdSe/ZnS heteronanocrystals in their close proximity at chromaticity-coordinates (x,y)=(0.42,0.39) and correlated-color-temperature CCT=3135K. ©2009 Optical Society of America.

LEDs made of In(x)Ga(1-x)N and (Al(x)Ga(1-x))(1-y)In(y)P suffer from significantly reduced quantum efficiency and luminous efficiency in the green/yellow spectral ranges. To address these problems, we present the design, growth, fabrication, hybridization, and characterization of proof-of-concept green/yellow hybrid LEDs that utilize radiative and nonradiative [Forster resonance energy transfer (FRET)] energy transfers in their colloidal semiconductor nanocrystals (NCs) integrated on near-UV LEDs. In our first NC-LED, we realize a color-converted LED that incorporate green-emitting CdSe/ZnS core/shell NCs (lambda(PL) = 548 nm) on near-UV InGaN/GaN LEDs (lambda(EL) = 379 nm). In our second NC-LED, we implement a color-converted FRET-enhanced LED. For that, we hybridize a custom-design assembly of cyan-and green-emitting CdSe/ZnS core/shell NCs (lambda(PL) = 490 and 548 nm) on near-UV LEDs. Using a proper mixture of differently sized NCs, we obtain a quantum efficiency enhancement of 9% by recycling trapped excitons via FRET. With FRET-NC-LEDs, we show that it is possible to obtain a luminous efficacy of 425 lm/W(opt) and a luminous efficiency of 94 lm/W, using near-UV LEDs with a 40% external quantum efficiency. Finally, we investigate FRET-converted light-emitting structures that use nonradiative energy transfer directly from epitaxial quantum wells to colloidal NCs. These proof-of-concept demonstrations show that FRET-based NC-LEDs hold promise for efficient solid-state lighting in green/yellow.

A comprehensive set of theoretical Coster-Kronig and fluorescence yields are presented for atomic numbers 18 less than or equal to Z less than or equal to 100. These quantities are based on ab initio relativistic calculations. Agreement with experimental values is fair for omega (1) and generally good for omega (2), omega (3) (Z greater than or equal to 54) [1]. Therefore, atomic L shell fluorescence (omega (1), omega (2), omega (3)) and Auger yields (a(1), a(2) and a(3)) for some elements in the atomic number range 59 less than or equal to Z less than or equal to 85 were determined. These selected measured semi-empirical values were also fitted by least squares to polynomials in the Z of the form Sigma (n)a(n)Z(n) and compared with theoretical and with earlier fitted values. (C) 2000 Elsevier Science B.V. All rights reserved.