The total electron charge density (shown in green) of a quantum dot of gallium arsenide, containing just 465 atoms

Effectively a quantum dot is something capable of confining a single electron or a few, and in which the electrons occupy discrete energy states just as they would in an atom. Quantum dots have been called artificial atoms, and in fact , and the ability to control energy states of the electrons by applying a voltage has led to the exotic idea of a material which can emulate different elements.

QUANTUM DOTS SOUND VERY EXOTIC and indeed they are in terms of the way they work which is dictated by the rules of quantum mechanics.

PROPERTIES

Tunable Emission PatternAn interesting property of quantum dots is that the peak emission wavelength is independent of the wavelength of the excitation light, assuming that it is shorter than the wavelength of the absorption onset. The bandwidth of the emission spectra, denoted as the Full Width at Half Maximum (FWHM) stems from the temperature, natural spectral line width of the quantum dots, and the size distribution of the population of quantum dots within a solution or matrix material. Spectral emission broadening due to size distribution is known as inhomogeneous broadening and is the largest contributor to the FWHM. Narrower size distributions yield smaller FWHM. For CdSe, a 5% size distribution corresponds to ~ 30nm FWHM.

Molecular CouplingColloidally prepared quantum dots are free floating and can be attached to a variety of molecules via metal coordinating functional groups. These groups

include but are not limited to thiol, amine, nitrile,phosphine, phosphine oxide, phosphonic acid, carboxylicacid or others ligands. This ability greatly increases the flexibility of quantum dots with respect to the types of environments in which they can be applied. By bonding appropriate molecules to the surface, the quantum dots can be dispersed or dissolved in nearly any solvent or incorporated into a variety of inorganic and organic films. In addition, the surface chemistry can be used to effectively alter the properties of the quantum dot, including brightness and electronic lifetime.

Tunable Absorption PatternIn addition to emissive advantages, quantum dots display advantages in their absorptive properties. In contrast to bulk semiconductors, which display a rather uniform absorption spectrum, the absorption spectrum for quantum dots appears as a series of overlapping peaks that get larger at shorter wavelengths. Owing once more to the discrete nature of electron energy levels in quantum dots, each peak corresponds to an energy transition between discrete electron-hole (exciton) energy levels. The quantum dots will not absorb light that has a wavelength longer than that of the first exciton peak, also referred to as the absorption onset. Like all other optical and electronic properties, the wavelength of the first exciton peak (and all subsequent peaks) is a function of the composition and size of the quantum dot. Smaller quantum dots result in a first exciton peak at shorter wavelengths.

Optical PropertiesAn immediate optical feature of colloidal quantum dots is their coloration. While the material which makes up a quantum dot defines its intrinsic energy signature, the nanocrystal's quantum confined size is more significant at energies near the band gap. Thus quantum dots of the same material, but with different sizes, can emit light of different colors. The physical reason is the quantum confinement effect. The larger the dot, the redder (lower energy) is its fluorescence spectrum. Conversely, smaller dots emit bluer (higher energy) light. The coloration is directly related to the energy levels of the quantum dot. Quantitatively speaking, the band gap energy that determines the energy (and hence color) of the fluorescent light is inversely proportional to the square of the size of the quantum dot. Larger quantum dots have more energy levels which are also more closely spaced. This allows the quantum dot to absorb photons containing less energy, i.e., those closer to the red end of the spectrum. Recent Observations have shown that the shape of the Crystal lattice also might change the color

Quantum Dots - Quantum YieldThe percentage of absorbed photons that result in an emitted photon is called Quantum Yield (QY). QY is controlled by the existence of nonradiative transition of electrons and holes between energy levels transitions that

produce no electromagnetic radiation. Nonradiative recombination largely occurs at the dot's surface and is therefore greatly influenced by the surface chemistry.

Adding Shells to Quantum Dots:Capping a core quantum dot with a shell (several atomic layers of an inorganic wide band semiconductor) reduces non-radiative recombination and results in brighter emission, provided the shell is of a different semiconductor material with a wider band gap than the Core semiconductor material.The higher QY of Core-Shell quantum dots comes about due to changes in the surface chemistry of the core quantum dot. The surface of quantum dots that lack a shell has both free (unbonded) electrons, in addition to crystal defects. Both ofthese characteristics tend to reduce QY by allowing for nonradiative electron energy transitions at the surface.The addition of a shell reduces the opportunities for these nonradiative transitions by giving conduction band electrons an increased probability of directly relaxing to the valence band.The shell also neutralizes the effects of many types of surface defects.

PRODUCTIONThere are several ways to confine excitons in semiconductors, resulting in different methods to produce quantum dots. In general, quantum wires, wells and dots are grown by advanced epitaxial techniques in nanocrystals produced by chemical methods or by ion implantation, or in nanodevices made by state-of-the-art lithographic techniques.

Colloidal synthesisColloidal semiconductor nanocrystals are synthesized from precursor compounds dissolved in solutions, much like traditional chemical processes. The synthesis of colloidal quantum dots is based on a three-component system composed of: precursors, organic surfactants, and solvents. When heating a reaction medium to a sufficiently high temperature, the precursors chemically transform into monomers. Once the monomers reach a high enough supersaturation level, the nanocrystal growth starts with a nucleation process. The temperature during the growth process is one of the critical factors in determining optimal conditions for the nanocrystal growth. It must be high enough to allow for rearrangement and annealing of atoms during the synthesis process while being low enough to promote crystal growth. Another critical factor that has to be stringently controlled during nanocrystal growth is the monomer concentration. The growth process of nanocrystals can occur in two different regimes, “focusing” and “defocusing”. At high monomer concentrations, the critical size (the size

where nanocrystals neither grow nor shrink) is relatively small, resulting in growth of nearly all particles. In this regime, smaller particles grow faster than large ones (since larger crystals need more atoms to grow than small crystals) resulting in “focusing” of the size distribution to yield nearly monodisperse particles. The size focusing is optimal when the monomer concentration is kept such that the average nanocrystal size present is always slightly larger than the critical size. When the monomer concentration is depleted during growth, the critical size becomes larger than the average size present, and the distribution “defocuses” as a result of Ostwald ripening.There are colloidal methods to produce many different semiconductors. Typical dots are made of binary alloys such as cadmium selenide, cadmium sulfide, indium arsenide, and indium phosphide. Although, dots may also be made from ternary alloys such as cadmium selenide sulfide, these quantum dots can contain as few as 100 to 100,000 atoms within the quantum dot volume, with a diameter of 10 to 50 atoms. This corresponds to about 2 to 10 nanometers, and at 10 nm in diameter, nearly 3 million quantum dots could be lined up end to end and fit within the width of a human thumb.Large batches of quantum dots may be synthesized via colloidal synthesis. Due to this scalability and the convenience of benchtop conditions, colloidal synthetic methods are promising for commercial applications. It is acknowledged to be the least toxic of all the different forms of synthesis.

FabricationSelf-assembled quantum dots are typically between 5 and 50 nm in size. Quantum dots defined by lithographically patterned gate electrodes, or by etching on two-dimensional electron gases in semiconductor heterostructures can have lateral dimensions exceeding 100 nm.Some quantum dots are small regions of one material buried in another with a larger band gap. These can be so-called core-shell structures, e.g., with CdSe in the core and ZnS in the shell or from special forms of silica called ormosil.Quantum dots sometimes occur spontaneously in quantum well structures due to monolayer fluctuations in the well's thickness.Self-assembled quantum dots nucleate spontaneously under certain conditions during molecular beam epitaxy (MBE) and metallorganic vapor phase epitaxy (MOVPE), when a material is grown on a substrate to which it is not lattice matched. The resulting strain produces coherently strained islands on top of a two-dimensional "wetting-layer." This growth mode is known as Stranski–Krastanov growth. The islands can be subsequently buried to form the quantum dot. This fabrication method has potential for applications in quantum cryptography (i.e. single photon sources) and quantum computation. The main limitations of this method are the cost of fabrication and the lack of control over positioning of individual dots.Individual quantum dots can be created from two-dimensional electron or hole gases present in remotely doped quantum wells or semiconductor

heterostructures called lateral quantum dots. The sample surface is coated with a thin layer of resist. A lateral pattern is then defined in the resist by electron beam lithography. This pattern can then be transferred to the electron or hole gas by etching, or by depositing metal electrodes (lift-off process) that allow the application of external voltages between the electron gas and the electrodes. Such quantum dots are mainly of interest for experiments and applications involving electron or hole transport, i.e., an electrical current.The energy spectrum of a quantum dot can be engineered by controlling the geometrical size, shape, and the strength of the confinement potential. Also, in contrast to atoms, it is relatively easy to connect quantum dots by tunnel barriers to conducting leads, which allows the application of the techniques of tunneling spectroscopy for their investigation.The quantum dot absorption features correspond to transitions between discrete,three-dimensional particle in a box states of the electron and the hole, both confined to the same nanometer-size box.These discrete transitions are reminiscent of atomic spectra and have resulted in quantum dots also being called artificial atoms. Confinement in quantum dots can also arise from electrostatic potentials (generated by external electrodes, doping, strain, or impurities).

Viral assemblyLee et al. (2002) reported using genetically engineered M13 bacteriophage viruses to create quantum dot biocomposite structures. As a background to this work, it has previously been shown that genetically engineered viruses can recognize specific semiconductor surfaces through the method of selection by combinatorial phage display.[11] Additionally, it is known that liquid crystalline structures of wild-type viruses (Fd, M13, and TMV) are adjustable by controlling the solution concentrations, solution ionic strength, and the external magnetic field applied to the solutions. Consequently, the specific recognition properties of the virus can be used to organize inorganic nanocrystals, forming ordered arrays over the length scale defined by liquid crystal formation. Using this information, Lee et al. (2000) were able to create self-assembled, highly oriented, self-supporting films from a phage and ZnS precursor solution. This system allowed them to vary both the length of bacteriophage and the type of inorganic material through genetic modification and selection.

Electrochemical assemblyHighly ordered arrays of quantum dots may also be self-assembled by electrochemical techniques. A template is created by causing an ionic reaction at an electrolyte-metal interface which results in the spontaneous assembly of nanostructures, including quantum dots, onto the metal which is then used as a mask for mesa-etching these nanostructures on a chosen substrate.

Bulk-manufactureConventional, small-scale quantum dot manufacturing relies on a process called “high temperature dual injection” which is impractical for most commercial applications that require large quantities of quantum dots.A reproducible method for creating larger quantities of consistent, high-quality quantum dots involves producing nanoparticles from chemical precursors in the presence of a molecular cluster compound under conditions whereby the integrity of the molecular cluster is maintained and acts as a prefabricated seed template. Individual molecules of a cluster compound act as a seed or nucleation point upon which nanoparticle growth can be initiated. In this way, a high temperature nucleation step is not necessary to initiate nanoparticle growth because suitable nucleation sites are already provided in the system by the molecular clusters. A significant advantage of this method is that it is highly scalable.

Cadmium-free quantum dotsCadmium-free quantum dots are also called “CFQD”. In many regions of the world there is now a restriction or ban on the use of heavy metals in many household goods which means that most cadmium based quantum dots are unusable for consumer-goods applications.For commercial viability, a range of restricted, heavy metal-free quantum dots have been developed showing bright emissions in the visible and near infra-red region of the spectrum and have similar optical properties to those of CdSe quantum dots.Cadmium and other restricted heavy metals used in conventional quantum dots is of a major concern in commercial applications. For Quantum Dots to be commercially viable in many applications they must not contain cadmium or other restricted metal elements. A new type of CFQD can be made from rare earth (RE) doped oxide colloidal phosphor nanoparticles. Unlike semiconductor nanoparticles, excitation was due to UV absorption of host material, which is same for different RE doped materials using same host. Multiplexing applications can be thus realized. The emission depends on the type of RE, which enables very large stokes shift and is narrower than CdSe QDs. The synthesis is aqueous based, which eliminated issues of water solubility for biological applications. The oxide surface might be easier for chemical functionalizion more and chemically stable in various environments. Some reports exist concerning the use of such phosphor nanoparticles on biological targeting and imaging.

APPLICATIONS

ComputingQuantum dot technology is one of the most promising candidates for use in solid-state quantum computation. By applying small voltages to the leads, the flow of electrons through the quantum dot can be controlled and thereby precise measurements of the spin and other properties therein can be made. With several entangled quantum dots, or qubits, plus a way of performing operations, quantum calculations and the computers that would perform them might be possible.

Biology

a) Analyte detection by quenching of the quantum dot fluorescence (red) upon binding of the analyte (black) to the quantum dot surface. b) By binding an appropriate organic fluorophore (green) as acceptor to the surface of the donor quantum dot fluorescence resonance energy transfer (FRET) occurs. FRET is stopped upon displacement of the acceptor dye from the quantum dots surface by the analyte. c) Specific cellular receptors (black) can be labeled with quantum dots that have been modified with appropriate ligand molecules. d) If a cell (grey) within a cell colony is labeled with quantum dots this cells passes the quantum dots to all its daughter cells and the fate of this cell can be observed.

In particular, they could have a considerable impact in single molecule tracing studies, in FRET based immunoassays, and in tracking the fate of cells in tissues.

As active sensor elements the fluorescence properties of the QDs are changed upon reaction with the analyte. While these applications are fairly simple, they appear to be restricted to sense just a few reactive small molecules or ions that are able to interact directly with the QDs' surface. Moreover, the reactions are usually not highly specific, and they also depend strongly on the surface properties of the QDs (including their coating).

It has been predicted that the use of QDs as active element in sensors in industrial applications will be limited. The use of QDs as passive labels in sensor applications, in particular in FRET based assays is much more promising.

In passive label probes, selective receptor molecules such as antibodies have been conjugated to the surface of QDs. In a first step, capture antibodies are immobilized on a substrate to which the analyte is added. In a second step QD-labeled antibodies are used to visualize and quantify the bound analyte. This technique allows for the design of simple multiplexed immunoassays.

QDs will have a huge potential for cellular labeling. Here, individual molecules can be fluorescence-labeled with QDs to trace the movement of individual membrane proteins. Also, whole cellular structures, such as DNA, can be QD-labeled and used as a fluorescent in situ marker.

However, some problems still have to be overcome. One of them is the potential cytotoxicity, especially of the cadmium-containing materials.

While coverage of potentially toxic particles with additional shells can seal the Cd-containing core, in the future other QDs that do not contain cadmium and therefore are more biocompatible will be made available, such as for example doped zinc selenide particles.

It has been estimated that quantum dots are 20 times brighter and 100 times more stable than traditional fluorescent reporters. For single-particle tracking, the irregular blinking of quantum dots is a minor drawback.The usage of quantum dots for highly sensitive cellular imaging has seen major advances over the past decade. The improved photostability of quantum dots, for example, allows the acquisition of many consecutive focal-plane images that can be reconstructed into a high-resolution three-dimensional image. Another application that takes advantage of the extraordinary photostability of quantum dot probes is the real-time tracking of molecules and cells over extended periods of time. Antibodies, streptavidin, peptides, nucleic acid aptamers, or small-molecule ligands can be used to target quantum dots to specific proteins on cells.

Photovoltaic cells

The technology utilizes semiconductor nanocrystals, or “quantum dots” — which slow the cooling of hot electrons to create time to grab them — and a titanium dioxide conductor to accomplish the task. A previous study pioneered the use of quantum dots to slow the electrons’ cooling. The recently documented breakthrough is significant for its use of an inexpensive titanium dioxide “wire.”

Light emitting devicesThere are several inquiries into using quantum dots as light-emitting diodes to make displays and other light sources, such as "QD-LED" displays, and "QD-WLED" (White LED). In June, 2006, QD Vision announced technical success in making a proof-of-concept quantum dot display and show a bright emission in the visible and near infra-red region of the spectrum. Quantum dots are valued for displays, because they emit light in very specific gaussian distributions. This can result in a display that more accurately renders the colors that the human eye can perceive. Quantum dots also require very little power since they are not color filtered. Additionally, since the discovery of "white-light emitting" QD, general solid-state lighting applications appear closer than ever. A color liquid crystal display (LCD), for example, is usually powered by a single fluorescent lamp (or occasionally, conventional white LEDs) that is color filtered to produce red, green, and blue pixels. Displays that intrinsically produce monochromatic light can be more efficient, since more of the light produced reaches the eye.

THE NANO DOT REVOLUTIONNanodot technology is a new process that has been developed over the past few years and some believe is set to revolutionise the print market. More specifically, it will almost certainly have a dramatic influence on the field of large format inkjet sublimation. The process ensures optimal pigment dispersion due to a combination of reducing the nanoparticles combined with fixing ionic polymers on the actual particles. To those of us without a science degree, in a nutshell this ensures improved ink flow, faster drying and better stability during the print process. However, due to the huge production investment in the latest laser spectrometers and medical filtration systems involved in producing nanodot inks, only one European company is currently producing them.

Originally developed in Italy, many countries such as Australia and Germany have started to use the nanodot technology with great success. This

significant new technology was introduced in the Italian sportswear and garment manufacturing sector last summer, causing an unprecedented wave of production houses to change inks. At the same time, some major German flag makers began using this new ink technology and saw impressive results. The flag manufacturing industry is notorious for its highly competitive price structure, so when one company starts using a new form of technology to improve results and cut production costs, its competitors are keen to find out what's going on. Thus far, the UK has been slow off the mark in making use of this new technology - but that is set to change later in 2008.

Nano Pigmentation Technology (NPT) - how it works

As with many great innovations, the theory behind Nano Pigmentation Technology (NPT) is relatively simple. "With NPT sublimation ink, the dye particles are ground to sub micron size and ionically fixed," "The combination of minute sizing and the fixing process reduces friction as the inks pass through the printing heads, yielding a more even dispersement within the ink fluid itself. This more even dispersement allows a denser concentration of dye to be used and less water is needed to reach the optimum viscosity for peizo heads."With versatility an important part of the printing process, various NPT inks have been developed for use on a range of different sublimation applications. When transfer printing, the lower water/dye ratio has the advantage of less paper cockling - and even offers the possibility of using a more cost effective, lighter 100g paper.Companies using the inks when working with direct to textile printing have reported that the NPT inks bleed less and show higher colour values resulting in a higher quality print. Add to this the advantages of a faster drying and pressing times reducing production times further - and as we all know, time is money, whatever marketplace your organisation operates in.

Extensively TestedDuring the development and testing phase, creators experimented with direct printing to coated and some uncoated textiles - resulting in a faster and more reliable result, in many cases. "Tests revealed that, no matter how the print was produced, if NPT inks were used with a good ICC profile, significantly less ink was used, due to the high dye density," "Combined with the drop in downtime caused by fewer head clogs and with less heat build up at the head prolonging the life of the print head itself, users have reported a potentially huge impact on reducing production costs."

It also claims improved ink stability during transport and storage, ensuring superior batch quality and consistent results for the user. Increased ease and speed of ink production at J-Tecks Como, Italy production plant, using new high tech ink processing equipment ensures faster ink production times. "As a company we have invested a lot of time and money in the technology to fully develop and test our product before we released it on to the market," comments J-Teck's President Dr. Gianni Cavallini. "Our stringent quality control procedures and faster production have enabled us to produce several different ink types and colours which cover specialist sublimation techniques. Tests show that they have an industry beating wash fastness and weatherability."

Embracing the change to stay competitivePrinting, perhaps more than many industries, is keen to embrace a new technology if a competitive advantage can be gained. If it enables us to do things faster, better , more cheaply and still stay reliable it is surely an innovation worth having. Only time will tell whether this is the start of a genuine revolution in the type of sublimation ink] that becomes the industry standard, but if the early results across other European countries are typical, Nantodot Pigment Technology is likely to here making an impact for the foreseeable future.

POTENTIAL APPROACH

Give headingInitial studies of polymer dyeing with quantum dots have involved brightly colored (but non-emissive) metal nanoparticles coated with low refractive index hydrogel layers. While such materials bear little relation to polymers used in the textile industry, they have many advantageous properties in terms of ease of synthesis, tunability, and optical characterization. The specific system studied is that of 12-nm diameter Au particles coated with a thick (~80 nm) layer of poly-N-isopropylacrylamide (p-NIPAm) to yield a monodisperse (<15% polydispersity) sol of polymer-clad Au particles. In aqueous media, p-NIPAm displays a temperature-dependent degree of solvation which can be used to thermally tune the refractive index of the cladding (Scheme I).

In this fashion, we can elucidate the optical properties of many different dielectric/metal composites from a single colloidal sol. Furthermore, we can easily control the number of Au particles per dielectric sphere, thereby allowing easy interrogation of “particle dye” concentration effects.

Figure 1 shows representative UV-Visible extinction spectra for bare Au particles, and polymer particles with two different Au concentrations (25-fold difference). It should be stated that all Au particles are associated with a polymer sphere; no free Au exists following polymerization. A number of key features in these spectra should be noted. First, the bare Au particles display the typical plasmon absorption band at about 520 nm; a solution of these particles is a deep burgundy color. The dielectric-coated particles, however, have a broad scattering background that largely obscures the Au plasmon absorption. Indeed, at the low Au concentration, the band is completely invisible. These spectra do not accurately reflect the visual appearance of the samples, however. The low Au concentration sample is a pinkish material, while the higher concentration yields an almost purple polymer solution. The combination of light transmission, reflection, and diffuse scattering yield samples have very different visual qualities. The effect of cladding refractive index and Au particle size on the optical properties of these materials is currently under investigation. The use of periodic dielectric structures, specifically colloidal crystals, for use in diffractive (non-chromophore based) textile colorant applications is also being studied. Colloidal crystals or artificial opals are now widely used in the fabrication of photonic materials for a variety of applications, largely because of the relative ease with which such structures can be assembled. Furthermore, the ability to tune the color of reflected light is easily accomplished by either changing the particle size, spacing, or in the case of

the hydrogel colloidal crystals developed in the Lyon group, by changing the compression of deformable particles. The building blocks for these soft colloidal crystals are microgels composed of the thermoresponsive polymer poly-N-isopropylacrylamide (pNIPAm) crosslinked with N,N’-methylenebisacrylamide. Monodisperse, spherical particles were prepared by precipitation polymerization in aqueous media as described previously.

Using this method, the resultant particle size can be continuously varied from ~50-nm to 1-μm diameter by controlling the surfactant and initiator concentrations.

For typical crosslinking densities of 2 mol-%, the resultant microgels undergo an ~15-fold decrease in volume due to water expulsion at the volume phase transition temperature (32 °C). The assembly of close-packed colloidal crystals takes place via a simple multistep process in which the thermoresponsivity of the component nanoparticles is exploited to obtain ordering. Initially, a solution of hydrogel nanoparticles is concentrated via centrifugation at a temperature below the phase transition temperature (25 °C). This produces a polymer mass at the bottom of the tube that is optically transparent with a faint blue, green or red opalescence, where the specific color properties depend on the initial particle concentration, centrifugation time, particle size, and centrifugation speed. The volume phase transition can then be used to anneal defects out of the crystal or to make a processable photonic material. Above the volume phase transition, the material is a low viscosity fluid, as the particles occupy a low volume fraction of the material. However, when lowering the temperature swells the particles, the viscosity increases dramatically, thereby “locking” the material in place. Post treatment such as photocrosslinking can then be used to create a temperature stable and permanent color element.

A typical image (obtained by differential interference contrast microscopy) of a hydrogel colloidal crystal is shown in Figure 2.

This image illustrates that the crystal is composed of a highly ordered, close-packed arrangement of spherical hydrogel particles. Since the component particles are soft and hydrated, the lattice spacing can be manipulated by changing the water content of the particles.

This effect is illustrated in Figure 3.

Here a single particle size has been used to create crystals of three distinct colors. Using this technique, we have demonstrated the ability to tune the color of a crystal over >150 nm. Furthermore, these materials display brilliant opalescence when the angle of observation is changed, thereby providing opportunities for even greater control over the color properties. Studies in the context of fiber coating and fiber filling for colorant applications are being done. For example, hollow core fibers will be filled by capillary action when the crystals are in their fluid form, followed by cooling to the viscous form. We will then study the color properties of these fibers as a function of internal core diameter, original crystal color, fiber conformation (to study angle dependent opalescence), and fiber refractive index. In parallel, we will investigate the coating of solid fibers with both standard and complex shapes, to investigate the color dispersion properties in the presence of diffractive, wavelength selecting coatings. Together, these studies will allow for a better understanding of how diffractive colorants can be used to impart non-chromophoric optical properties to textile fibers. Fibers have been made which have photoluminescent particles and the optical properties of such fibers have been studied. The fibers and the photoluminescent particles were obtained from Score Technologies. A typical emission spectra is shown in Figure 4 obtained using a microspectrometer. The fiber emits in the green-yellow part of the visible spectrum.

Coloration of textiles with self-dispersible carbon black nanoparticles

Cotton, wool, acrylic and nylon fabrics can be directly dyed by using surface modified carbon black (CB), self-dispersible carbon black (SDCB), nanoparticles through an exhaustion process. The SDCB nanoparticles were

prepared by refluxing CB particles in nitric acid for certain time to result in hydrophilic carboxylic groups on their surfaces. The SDCB nanoparticles behaved similarly to direct or acid dyes in dyeing cotton, acrylic and nylon fibers. The SDCB nanoparticles were characterized by infrared spectroscopy and particle size analyzer. The SDCB-dyed fabrics showed good colorfastness against crocking. However, the wash fastness of the nanoparticle-dyed cotton fabrics is relatively lower than the crocking fastness due to the hydrophilic feature of the SDCB nanoparticles.

Comparison of properties of organic dyes and QuantumDots

Property Organic dye QDa

Absorption spectra

Discrete bands, FWHMb 35 nmc to 80–100 nmd

Steady increase toward UV wavelengths starting from absorption onset;

enables free selection of excitation wavelength

Molar absorption coefficient

2.5 104–2.5 105 M-1 cm-1 (at long-wavelength

absorption maximum)

105–106 M-1 cm-1 at first exitonic absorption peak,

increasing toward UV wavelengths; larger

(longer wavelength) QDs generally have higher

absorption

Emission spectra

Asymmetric, often tailing to long-wavelength side; FWHM,

35 nmc to 70–100 nmd

Symmetric, Gaussian profile; FWHM, 30–90 nm

Stokes shiftNormally <50 nmc, up to

>150 nmd

Typically <50 nm for visible wavelength–

emitting QDs

Quantum yield0.5–1.0 (visiblee), 0.05–0.25

(NIRe)0.1–0.8 (visible), 0.2–0.7

(NIR)

Fluorescence lifetimes

1–10 ns, mono-exponential decay

10–100 ns, typically multi-exponential decay

Two-photon action cross-

section

1 10-52–5 10-48 cm4 s photon-1 (typically about 1

10-49 cm4 s photon-1)

2 10-47–4.7 10-46 cm4 s photon-1

Solubility or dispersibility

Control by substitution pattern

Control via surface chemistry (ligands)

Binding to biomolecules

Via functional groups following established

protocols Often several dyes bind to a single biomolecule Labeling-induced effects on spectroscopic properties of reporter studied for many

common dyes

Via ligand chemistry; few protocols available

Several biomolecules bind to a single QD Very little information available on labeling-induced effects

Size 0.5 nm; molecule6–60 nm (hydrodynamic

diameter); colloid

Thermal stability

Dependent on dye class; can be critical for NIR-wavelength

dyes

High; depends on shell or ligands

Photochemical stability

Sufficient for many applications (visible

wavelength), but can be insufficient for high-light flux

applications; often problematic for NIR-

wavelength dyes

High (visible and NIR wavelengths); orders of magnitude higher than

that of organic dyes; can reveal photobrightening

ToxicityFrom very low to high;

dependent on dye

Little known yet (heavy metal leakage must be

prevented, potential nanotoxicity)

Reproducibility of labels (optical, chemical

properties)

Good, owing to defined molecular structure and established methods of

characterization; available from commercial sources

Limited by complex structure and surface

chemistry; limited data available; few commercial

systems available

Applicability to single-molecule

analysis

Moderate; limited by photobleaching

Good; limited by blinking

FRET

Well-described FRET pairs; mostly single-donor– single-

acceptor configurations; enables optimization of

reporter properties

Few examples; single-donor–multiple-acceptor configurations possible;

limitation of FRET efficiency due to

nanometer size of QD coating

Spectral multiplexing

Possible, 3 colors (MegaStokes dyes), 4 colors (energy-transfer cassettes)

Ideal for multi-color experiments; up to 5 colors demonstrated

Lifetime multiplexing

Possible

Lifetime discrimination between QDs not yet

shown; possible between QDs and organic dyes

Signal amplification

Established techniques

Unsuitable for many enzyme-based

techniques, other techniques remain to be

adapted and/or established

Properties of organic dyes are dependent on dye class and are tunable via substitution pattern. Properties of QDs are dependent on material, size, size distribution and surface chemistry.

aEmission wavelength regions for QD materials (approximate): CdSe, 470–660 nm; CdTe, 520–750 nm; InP, 620–720 nm; PbS, >900 nm; and PbSe, >1,000 nm.

bFWHM, full width at half height of the maximum.

cDyes with resonant emission such as fluoresceins, rhodamines and cyanines.

dCT dyes.

eDefinition of spectral regions used here: visible, 400–700 nm; and NIR, > 700 nm.

Unless stated otherwise, all values were determined in water for organic dyes and in organic solvents for QDs, and refer to the free dye or QD.

CONCLUSION

Hence it can be concluded that quantum dots to be used as textile dyes offer immense potential. If successful, the breakthrough can contribute greatly to reduce the pollution caused by the textile industry and help in a sustainable development.

References

http://inhabitat.com/new-quantum-dot-solar-cells-could-double-efficiency/

National textile report -C00-G03

Cientifica quantum dots –technology white papers

Coloration of textiles with self-dispersible carbon black nanoparticles by Dapeng Li1, Gang Sun*