Sideways scattering in double resonant plasmonic nanostructures for light harvesting applications.

Numerical simulations of light scattering by elongated metal nanoparticles in an asymmetric arrangement show resonant scattering in two near-infrared wavelength ranges associated with different surface plasmon modes. The main scattering directions of the two plasmon modes are in opposite diagonal directions and almost perpendicular to each other. At wavelengths in-between the two plasmon resonances our simulations showed for the first time strong scattering at approximately ± 90°, which is parallel to the incident electric field direction.

Low-power upconversion in dye-doped polymer nanoparticles.

Examples of nanoscale low-power upconverting systems are rapidly increasing because of their potential application in numerous areas such as bioimaging or drug delivery. The fabrication of dye-doped cross-linked rubbery nanoparticles that exhibit upconversion even at relatively low power densities is reported here. The nanoparticles were prepared by surfactant-free emulsion polymerization of n-butylacrylate with divinylbenzene as a cross-linker, followed by dyeing of the resulting particles with a two-chromophore system composed of a palladium porphyrin sensitizer, and diphenylanthracene.

Highly twisted triarylamines for photoinduced intramolecular charge transfer.

9-(N,N-Dianisylamino)anthracene (9DAAA), 9-(N,N-dianisylamino)dinaphth([1,2-a:2'-1'-j]-anthracene (9DAAH), and 9,10-bis(N,N-dianisylamino)anthracene (910BAA) were synthesized as highly twisted triarylamines with potential for photoexcited internal charge transfer. Crystallography of 9DAAA shows its dianisylamino group to be twisted nearly perpendicular to its anthracene unit, similar to a report for 910BAA. The solution fluorescence spectra show strong bathochromic shifts for each of the three molecular systems with strongly decreased quantum efficiency in higher polarity solvents.

Efficient quantum dot-quantum dot and quantum dot-dye energy transfer in biotemplated assemblies.

CdSe semiconductor nanocrystal quantum dots are assembled into nanowire-like arrays employing microtubule fibers as nanoscale molecular "scaffolds." Spectrally and time-resolved energy-transfer analysis is used to assess the assembly of the nanoparticles into the hybrid inorganic biomolecular structure. Specifically, we demonstrate that a comprehensive study of energy transfer between quantum dot pairs on the biotemplate and, alternatively, between quantum dots and molecular dyes embedded in the microtubule scaffold comprises a powerful spectroscopic tool for evaluating the assembly process.

Time-resolved surface plasmon polariton coupled exciton and biexciton emission.

We discuss the coupling between optically excited semiconductor nanocrystals (NC) and thin metal films in both the single and multi-exciton regime. Using time-resolved photoluminescence spectroscopy, we determine the decay dynamics of free space and surface plasmon polariton (SPP) coupled emission. The two dynamics are found to be distinctly different at very small NC-metal separations and at photon energies close to the SPP resonance frequency.

A laser pointer driven microheater for precise local heating and conditional gene regulation in vivo. Microheater driven gene regulation in zebrafish.

Background: Tissue heating has been employed to study a variety of biological processes, including the study of genes that control embryonic development. Conditional regulation of gene expression is a particularly powerful approach for understanding gene function. One popular method for mis-expressing a gene of interest employs heat-inducible heat shock protein (hsp) promoters.

Block-copolymer-based plasmonic nanostructures.

We report on the fabrication and optical characterization of dense and ordered arrays of metal nanoparticles. The metal arrays are produced by reducing metal salts in block copolymer (BCP) templates made by solvent annealing of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) or poly(styrene-b-ethylene oxide) (PS-b-PEO) diblock copolymer thin films in mixed solvents. The gold and gold/silver composite nanoparticle arrays show characteristic surface plasmon resonances in the visible wavelength range.

Radiative rate enhancements in ensembles of hybrid metal-semiconductor nanostructures.

We report on radiative decay rate modifications of dipole emitters in the proximity of anisotropic metal nanostructures. Using time, angle, and polarization resolved photoluminescence spectroscopy, we show that resonant interactions between surface plasmons in gold nanodisks and excitons in semiconductor nanocrystals require both spectral and orientational overlap resulting in radiative rate enhancements with directional characteristics. Numerical simulations of emission decay dynamics based on local electric field enhancements are in excellent agreement with experimental results.

Single-exciton optical gain in semiconductor nanocrystals.

Nanocrystal quantum dots have favourable light-emitting properties. They show photoluminescence with high quantum yields, and their emission colours depend on the nanocrystal size--owing to the quantum-confinement effect--and are therefore tunable. However, nanocrystals are difficult to use in optical amplification and lasing.

Nanocrystal-based light-emitting diodes utilizing high-efficiency nonradiative energy transfer for color conversion.

We report a practical implementation of high-efficiency color conversion in an electrically pumped light-emitting diode (LED) using nonradiative energy transfer. On the basis of a new LED design that offers both strong energy-transfer coupling and efficient carrier injection, we show that a hybrid structure comprising a single monolayer of CdSe nanocrystals assembled on top of an InGaN/GaN quantum well provides nearly 10% color conversion efficiency. This value is significantly higher than that for a traditional absorption-re-emission color-conversion scheme in a similar device structure.

Effect of the thiol-thiolate equilibrium on the photophysical properties of aqueous CdSe/ZnS nanocrystal quantum dots.

We study the effect of thiols on the emission efficiency of aqueous CdSe/ZnS core/shell nanocrystal quantum dots (NQDs). We observe that the impact of thiol addition on emission quantum yields (QYs) is time-, concentration-, and pH-dependent. Further, we use a combination of time-resolved spectroscopic methods to determine the mechanism by which thiol addition can cause either increases or decreases in QYs.

Multicolor light-emitting diodes based on semiconductor nanocrystals encapsulated in GaN charge injection layers.

Numerous technologies including solid-state lighting, displays, and traffic signals can benefit from efficient, color-selectable light sources that are driven electrically. Semiconductor nanocrystals are attractive types of chromophores that combine size-controlled emission colors and high emission efficiencies with excellent photostability and chemical flexibility. Applications of nanocrystals in light-emitting technologies, however, have been significantly hindered by difficulties in achieving direct electrical injection of carriers.

Synthesis and characterization of Co/CdSe core/shell nanocomposites: bifunctional magnetic-optical nanocrystals.

Nanocomposite materials provide the possibility for multifunctional properties in contrast with their more-limited single-component counterparts. Here, we report the synthesis and characterization of the first all-inorganic core/shell hybrid magnetic-optical nanoparticle, cobalt/cadmium selenide. The core/shell nanocrystals are prepared in a facile one-pot reaction, and their microstructure is analyzed using low- and high-resolution transmission electron microscopy.

Energy-transfer pumping of semiconductor nanocrystals using an epitaxial quantum well.

As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies--for example, displays, fluorescence tagging, solid-state lighting and lasers. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals.