Interest In Quantum Dots Research Articles

Singlet oxygen generation by hybrid structures based on CdSe/ZnS quantum dots and tetraphenylporphyrin in organic medium

Photophysical properties of hybrid structures based on CdSe/ZnS quantum dots (QDs) and tetraphenylporphyrin (TPP) molecules have been studied. The hybrid structures are characterized by higher singlet oxygen (SO) generation compared to free TPP molecules due to high intracomplex Förster Resonance Energy Transfer (FRET) efficiency and saving TPP in the monomeric form in the hybrid structures. We show that all energy transferred from QDs to TPP is fully used to generate singlet oxygen since there are no new nonradiative channels in the structures. We believe that our result will stimulate renewed interest in QD based structures with photosensitizers as theranostics agents.

Photostability of Semiconductor Quantum Dots in Response to UV Exposure.

The interest in quantum dots (QDs) and their popularity in life science applications stems from their high photostability and unique optical properties such as superior light absorption. Photostability of semiconductor QDs is reportedly higher than that of organic dyes, but QDs may also be affected by light exposure. The outcome of such exposure may depend on many experimental factors, can lead to either an increase or decrease in the photoluminescent efficiency of QDs and is difficult to predict. QDs may therefore require experimental testing for their photostability especially prior to quantitative applications. A simple QD testing procedure described here showed a substantial degree of photobleaching when exposed to UV; nevertheless, the rate of change was noticeably lower than that measured for traditional organic dyes, as expected. The procedure reported is also applicable to traditional organic dyes and allows for quantitative comparisons to be conducted.

Wavelength-tunable InAsP quantum dots in InP nanowires

There is considerable interest in quantum dots incorporated in nanowires for nanolasers and quantum emitters. In this letter, we demonstrate single InAsP quantum dots embedded in InP nanowires grown by metalorganic vapor-phase epitaxy. Despite the abrupt change of growth conditions at the interface, InAsP quantum dots can be grown in pure wurtzite InP nanowires. We develop a model and analyze the effects of the thickness of InAsP quantum dots and the composition of As on the formation of dislocations. Furthermore, the InAsP/InP quantum dot nanowires show bright photoluminescence up to room temperature without any surface passivation. The emission from the quantum dots could be well tuned by adjusting the dot size either vertically or laterally. The study demonstrates the potential of this material system for optoelectronic applications.

High‐density quantum dots composites and its photolithographic patterning applications

With the growing interest in quantum dots (QDs), many applications are emerging recently. In particular, the display industry has shown widespread interest in using QDs as the next generation colorants. One application is to replace conventional color filters with QD‐based color conversion films to significantly improve color purity and luminous efficiency. However, QD blending which is capable of photolithographic patterning is a very challenging problem due to its low dispersion property and aggregations in polar medias. Herein, we report a photo‐patternable QD dispersion that can produce fine patterns through a photolithography process. First, the QDs dispersed in a nonpolar solvent, for example, chloroform or hexane, were separated and dried to obtain a QD powder. And then, the dispersion characteristics of the QD powders were investigated after mixing commercial dispersants and UV curable oligomers. Furthermore, the QD dispersion was investigated up to 30 wt.% of QDs by mixing with various commercial additives. We have studied the optical property changes of QDs during the photocuring process and the heating process prior to actual application. And, we have studied the surface characteristics of the fine QDs patterns after patterning process. As a result, it was confirmed that QDs are able to be well dispersed up to 30 wt.%.

A Millifluidic Reactor System for Multistep Continuous Synthesis of InP/ZnSeS Nanoparticles

AbstractDespite the growing interest in quantum dots for applications ranging from bioimaging to display technologies, the reproducible and high‐quality synthesis of Cd‐free quantum dots (QDs) on a large scale remains challenging. Conventional large‐scale batch synthesis techniques are limited by slow precursor heating/cooling/mixing, poor reproducibility and low productivity. In recent years, the continuous flow synthesis of QDs using microfluidic approaches has shown promise to overcome the shortcomings of batch synthesis. However, the application of microfluidic reactors for synthesis of Cd‐free QDs exhibiting high photoluminescence quantum yield (PL QY) at high production rate remains a challenge. Here, we report a modular millifluidic reactor for the fully continuous multi‐step synthesis of InP/ZnSeS core‐shell QDs, that integrates the precise control over reaction conditions with the potential for gram‐scale production rates. We use a design of experiment approach to understand and optimize the process parameters for the synthesis, resulting in PL QY up to 67% with good reproducibility in terms of both QY and peak position (less than 5% standard deviation). Additionally, by changing the process parameters for different reaction stages (core and shell reactors), the wavelength of the InP/ZnSeS particles can be tuned to cover nearly the entire visible spectrum (480–650 nm).

PHOTON GENERATION EFFICIENCY AND ENTANGLEMENT IN QUANTUM DOT SYSTEMS

The interest in quantum dots as sources of quantum light is based upon the potential for high photon generation efficiency that originates in their atom-like energy structure. Quantum dots can be excited resonantly and coherently, where generation of photon pairs calls for a specific excitation method of two-photon resonant excitation of the biexciton. Though this method is very efficient, it was very often showing sub-unity excitation efficiency that could be observed, for instance, in the maximum amplitude of the Rabi oscillations. Investigation of the dephasing processes in this excitation technique is of strategic interest for quantum communication technologies.

Imaging and Manipulating Energy Transfer Among Quantum Dots at Individual Dot Resolution

Many processes of interest in quantum dots involve charge or energy transfer from one dot to another. Energy transfer in films of quantum dots as well as between linked quantum dots has been demonstrated by luminescence shift, and the ultrafast time-dependence of energy transfer processes has been resolved. Bandgap variation among dots (energy disorder) and dot separation are known to play an important role in how energy diffuses. Thus, it would be very useful if energy transfer could be visualized directly on a dot-by-dot basis among small clusters or within films of quantum dots. To that effect, we report single molecule optical absorption detected by scanning tunneling microscopy (SMA-STM) to image energy pooling from donor into acceptor dots on a dot-by-dot basis. We show that we can manipulate groups of quantum dots by pruning away the dominant acceptor dot, and switching the energy transfer path to a different acceptor dot. Our experimental data agrees well with a simple Monte Carlo lattice model of energy transfer, similar to models in the literature, in which excitation energy is transferred preferentially from dots with a larger bandgap to dots with a smaller bandgap.

PHOTON GENERATION EFFICIENCY AND ENTANGLEMENT IN QUANTUM DOT SYSTEMS

The interest in quantum dots as sources of quantum light is based upon the potential for high photon generation efficiency that originates in their atom-like energy structure. Quantum dots can be excited resonantly and coherently, where generation of photon pairs calls for a specific excitation method of two-photon resonant excitation of the biexciton. Though this method is very efficient, it was very often showing sub-unity excitation efficiency that could be observed, for instance, in the maximum amplitude of the Rabi oscillations. Investigation of the dephasing processes in this excitation technique is of strategic interest for quantum communication technologies.

Diagnostic and Therapeutic Applications of Quantum Dots in Nanomedicine.

The interest in Quantum Dots as a class of nanomaterials has grown considerably since their discovery by Ekimov and Efros in the early 1980s. Although this early work focussed primarily on CdSe-based nanocrystals, the field has now expanded to include various classes of nanoparticles with different types of core, shell or passivation chemistry. Such differences can have a profound effect on the optical properties and potential biocompatibility of the resulting constructs. Although QDs have predominantly been used for imaging and sensing applications, more examples of their use as therapeutics are beginning to emerge. In this chapter we discuss the progress made over the past decade in developing QDs for imaging and therapeutic applications.

Revisiting elementary quantum mechanics with the BenDaniel-Duke boundary condition

The past decade has seen an upsurge of interest in quantum dots and nanostructures. These are essentially structures of size 1to10nm. We discuss a simplified model of a quantum dot in which we employ the effective mass approximation and the BenDaniel-Duke boundary condition. The latter accounts for the fact that the effective carrier mass inside the well, mi, is different from the mass outside, m0. The energies and the charge distributions in the nanostructure are determined by the mass discontinuity factor β=mi∕m0. The charge density at the interface becomes larger as β→0. We propose a novel quantum scale σ∼β2V0L2, where V0 is the barrier height and L is the well size. The scale σ represents a mass modified potential strength. An asymptotic analysis shows that the charge densities and energies of the carrier depend simply on σ. We also propose a definition of the penetration depth analogous to the one proposed by Garrett. Our study of tunneling reveals that the one-dimensional analog of the Ramsauer-Townsend resonances becomes increasingly sharp and well defined as β→0.