Colloidal III–V Nitride Quantum Dots

Colloidal quantum dots (QDs) have attracted intense attention in both fundamental studies and practical applications. To date, the size, morphology, and composition-controlled syntheses have been successfully achieved in II–VI semiconductor nanocrystals. Recently, III-nitride semiconductor quantum dots have begun to draw significant interest due to their promising applications in solid-state lighting, lasing technologies, and optoelectronic devices. The quality of nitride nanocrystals is, however, dramatically lower than that of II–VI semiconductor nanocrystals. In this review, the recent development in the synthesis techniques and properties of colloidal III–V nitride quantum dots as well as their applications are introduced

Sideband pump-probe technique resolves nonlinear modulation response of PbS/CdS quantum dots on a silicon nitride waveguide

For possible applications of colloidal nanocrystals in optoelectronics and nanophotonics, it is of high interest to study their response at low excitation intensity with high repetition rates, as switching energies in the pJ/bit to sub-pJ/bit range are targeted. We develop a sensitive pump-probe method to study the carrier dynamics in colloidal PbS/CdS quantum dots deposited on a silicon nitride waveguide after excitation by laser pulses with an average energy of few pJ/pulse. We combine an amplitude modulation of the pump pulse with phase-sensitive heterodyne detection. This approach permits to use co-linearly propagating co-polarized pulses. The method allows resolving transmission changes of the order of 10(-5) and phase changes of arcseconds. We find a modulation on a sub-nanosecond time scale caused by Auger processes and biexciton decay in the quantum dots. With ground state lifetimes exceeding 1 mu s, these processes become important for possible realizations of opto-electronic switching and modulation based on colloidal quantum dots emitting in the telecommunication wavelength regime

“Green” Quantum Dots: Basics, Green Synthesis, and Nanotechnological Applications

Nanotechnological development of new materials involves the discovery or design of materials at small length scales with controlled physical and chemical properties than can be tuned or modified in function of their applications. One of the most suitable examples of nanoparticles used for this purpose are quantum dots, a type of colloidal fluorescent semiconducting nanocrystalline material that has the possibility, due to its unique optical and electronic properties, to be used in numerous technological applications such as biosensing, in vivo imaging techniques, photovoltaics, nanomedicine, molecular pathology, and drug delivery. Thus, there are almost endless possibilities for quantum dots materials. In spite of the fast advance in the search of quantum dots with better nanomaterial performance, environmentally benign and sustainable production is still lacking. Although the use of these materials is developing promptly, there is increasing concern that these materials might pose potential risks to human health. Herein, we discuss principal properties of quantum dots, including their functional architecture and toxicity, and review the main studies about “green” quantum dots synthesis to be aligned with green nanotechnology approach for nontoxic, cleaner, safer, and more responsible processes. The organometallic colloidal synthesis and the aqueous colloidal synthesis, as well as their drawbacks and benefits, are conferred. Recent advances in technological and biological quantum dots–based applications are also discussed in this chapter

Colloidal Quantum Dot Based Photonic Circuits and Devices

Colloidal quantum dots have desirable optical properties which can be exploited to realize a variety of photonic devices and functionalities. However, colloidal dots have not had a pervasive utility in photonic devices because of the absence of patterning methods. The electronic chip industry is highly successful due to the well-established lithographic procedures. In this thesis we borrow ideas from the semiconductor industry to develop lithographic techniques that can be used to pattern colloidal quantum dots while ensuring that the optical properties of the quantum dots are not affected by the process. In this thesis we have developed colloidal quantum dot based waveguide structures for amplification and switching applications for all-optical signal processing. We have also developed colloidal quantum dot based light emitting diodes. We successfully introduced CdSe/ZnS quantum dots into a UV curable photo-resist, which was then patterned to realize active devices. In addition, passive devices (devices without quantum dots) were integrated to active devices via waveguide couplers. Use of photo-resist devices offers two distinct advantages. First, they have low scattering loss and secondly, they allow good fiber to waveguide coupling efficiency due to the low refractive index which allows for large waveguide cross-sections while supporting single mode operation. Practical planar photonic devices and circuits incorporating both active and passive structures can now be realized, now that we have patterning capabilities of quantum dots while maintaining the original optical attributes of the system. In addition to the photo-resist host, we also explored the incorporation of colloidal quantum dots into a dielectric silicon dioxide and silicon nitride one-dimensional microcavity structures using low temperature plasma enhanced chemical vapor deposition. This material system can be used to realize microcavity light emitting diodes that can be realized on any substrate. As a proof of concept demonstration we show a 1550 nm emitting all-dielectric vertical cavity structure embedded with PbS quantum dots. Enhancement in spontaneous emission from the dots embedded in the microcavity is also demonstrated

Preparation and Characterization of Self-Assembled Thin Film of MPS-Capped ZnS Quantum Dots for Optical Applications

For this study, we prepared colloidal ZnS quantum dots using 3-mercaptopropyltrimethoxysilane (MPS) as the capping agent. Colloidal ZnS quantum dots were directly deposited on glass substrates by a spin coating process. Therefore, self-assembled films made of ZnS quantum dots in a SiO2 network were obtained using only one production step. The films were heat-treated at 100°, 125°, 150°, 175° and 200°C in an N2 atmosphere. The results showed that the dimension of quantum dots changed from 2.8 nm to 3.2 nm by heat treatment. The refractive index, extinction coefficient, thickness, and dielectric coefficient values of the films were calculated. The present study showed that size and the refractive indices of films can be controlled by the heat treatment. Therefore, such films can be a good candidate in optical filter applications

InAs colloidal quantum dots synthesis via aminopnictogen precursor chemistry

Despite their various potential applications, InAs colloidal quantum dots have attracted considerably less attention than more classical II-VI materials because of their complex syntheses that require hazardous precursors. Recently, aminophosphine has been introduced as a cheap, easy-to-use and efficient phosphorus precursor to synthesize InP quantum dots. Here, we use aminopnictogen precursors to implement a similar approach for synthesizing InAs quantum dots. We develop a two-step method based on the combination of aminoarsine as the arsenic precursor and aminophosphine as the reducing agent. This results in state-of-the-art InAs quantum dots with respect to the size dispersion and band gap range. Moreover, we present shell coating procedures that lead to InAs/ZnS(e) core/shell quantum dots that emit in the infrared region. This innovative synthesis approach can greatly facilitate the research on InAs quantum dots and may lead to synthesis protocols for a wide range of III-V quantum dots

Stable DHLA–PEG capped PbS quantum dots: from synthesis to near-infrared biomedical imaging

The short shelf-life of water-soluble quantum dots (QDs) due to colloidal instability represents a major drawback to their exploitation. This work examines the colloidal stability of PbS nanoparticles capped with dihydrolipoic acid–polyethylene glycol (DHLA–PEG) ligands terminated with functional groups such as –NH 2 , –COOH, OMe and –N3 and their application for in vivo imaging. We prove a mechanism of colloidal instability and develop a strategy to produce for the first time stable PEG-capped PbS quantum dots with high quantum yield and optical emission in the first and the second near-infrared (NIR) windows of low absorption of biological tissues. The NIR imaging of in vivo biodistribution is demonstrated at wavelengths 4 1000 nm, with benefits of reduced tissue absorption and light scattering. The stability, biocompatibility and potential for further QD functionalization open up realistic prospects for non-invasive bioimaging applications

controlled coupling of a single quantum dot to a gold nanocone antenna

Multiexcitonic transitions and emission of several photons per excitation comprise a very attractive feature of semiconductor quantum dots for optoelectronics applications. However, these higher-order radiative processes are usually quenched in colloidal quantum dots by Auger and other nonradiative decay channels. To increase the multiexcitonic quantum efficiency, several groups have explored plasmonic enhancement, so far with moderate results. By controlled positioning of individual quantum dots in the near field of gold nanocone antennas, we enhance the radiative decay rates of monoexcitons and biexcitons by 109 and 100 folds at quantum efficiencies of 60 and 70%, respectively, in very good agreement with the outcome of numerical calculations. We discuss the implications of our work for future fundamental and applied research in nano-optics