Nanoparticles used to Monitor for Cancer


Breast cancer cellResearchers have developed new nanoparticles that can be used for magnetic resonance imaging (MRI). This application could help medics to monitor a tumor’s environment and to assess if drugs have successfully reached their targets. In a new study, medical technologists based at MIT have shown how nanoparticles, carrying special sensors for fluorescence and MRI, can be used to follow the progression of vitamin C in mice.

The research findings indicated that where there is a high concentration of vitamin C, the particles show a strong fluorescent signal but little MRI contrast. Conversely, where there was not much vitamin C, a stronger MRI signal was visible and the fluorescence was very weak. The nanoparticles circulated for several hours in a mouse’s bloodstream. This was sufficient time to track the progress of the vitamin C and to obtain images.

Molecular-Gears-3D-Model

For the next stage of the study, the researchers plan to use the nanoparticles to detect reactive oxygen species that tend to correlate with disease. This will be useful in helping to understand how a disease progresses.

Nanoparticles are particles between 1 and 100 nanometers in size (a nanometer is equal to one billionth of a metre.) Nanoparticle characterization is necessary to establish understanding and control of nanoparticle synthesis and applications, this is normally achieved by electron microscopy.

The nanoparticles form the new study were constructed from polymer chains. The chains carried either an organic MRI contrast agent, called a nitroxide, or a fluorescent molecule termed Cy5.5. The two types of particles are used together, at different ratios. This produces a single nanoparticle system.

Nitroxides are reactive molecules that contain a nitrogen atom bound to an oxygen atom with an unpaired electron. When the nitroxides encounter a molecule such as vitamin C they become inactive and Cy5.5 fluoresces.

The findings have been published in the journal Nature Communications. The paper is titled “Redox-responsive branched-bottlebrush polymers for in vivo MRI and fluorescence imaging.”

More about Nanoparticles, Cancer, Nanotechnology
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Beyond LEDs: Brighter, New Energy-Saving Flat Panel Lights Based on Carbon Nanotubes


CNT LEDs 50297Abstract:
Even as the 2014 Nobel Prize in Physics has enshrined light emitting diodes (LEDs) as the single most significant and disruptive energy-efficient lighting solution of today, scientists around the world continue unabated to search for the even-better-bulbs of tomorrow.

Beyond LEDs: Brighter, new energy-saving flat panel lights based on carbon nanotubes – Planar light source using a phosphor screen with highly crystalline single-walled carbon nanotubes (SWCNTs) as field emitters demonstrates its potential for energy-efficient lighting device

Washington, DC | Posted on October 14th, 2014

Enter carbon electronics.

Electronics based on carbon, especially carbon nanotubes (CNTs), are emerging as successors to silicon for making semiconductor materials. And they may enable a new generation of brighter, low-power, low-cost lighting devices that could challenge the dominance of light-emitting diodes (LEDs) in the future and help meet society’s ever-escalating demand for greener bulbs.

CNT LEDs 50297
Scientists from Tohoku University in Japan have developed a new type of energy-efficient flat light source based on carbon nanotubes with very low power consumption of around 0.1 Watt for every hour’s operation–about a hundred times lower than that of an LED.

In the journal Review of Scientific Instruments, from AIP publishing, the researchers detail the fabrication and optimization of the device, which is based on a phosphor screen and single-walled carbon nanotubes as electrodes in a diode structure. You can think of it as a field of tungsten filaments shrunk to microscopic proportions.

They assembled the device from a mixture liquid containing highly crystalline single-walled carbon nanotubes dispersed in an organic solvent mixed with a soap-like chemical known as a surfactant. Then, they “painted” the mixture onto the positive electrode or cathode, and scratched the surface with sandpaper to form a light panel capable of producing a large, stable and homogenous emission current with low energy consumption.

“Our simple ‘diode’ panel could obtain high brightness efficiency of 60 Lumen per Watt, which holds excellent potential for a lighting device with low power consumption,” said Norihiro Shimoi, the lead researcher and an associate professor of environmental studies at the Tohoku University.

Brightness efficiency tells people how much light is being produced by a lighting source when consuming a unit amount of electric power, which is an important index to compare the energy-efficiency of different lighting devices, Shimoi said. For instance, LEDs can produce 100s Lumen per Watt and OLEDs (organic LEDs) around 40.

Although the device has a diode-like structure, its light-emitting system is not based on a diode system, which are made from layers of semiconductors, materials that act like a cross between a conductor and an insulator, the electrical properties of which can be controlled with the addition of impurities called dopants.

The new devices have luminescence systems that function more like cathode ray tubes, with carbon nanotubes acting as cathodes, and a phosphor screen in a vacuum cavity acting as the anode. Under a strong electric field, the cathode emits tight, high-speed beams of electrons through its sharp nanotube tips — a phenomenon called field emission. The electrons then fly through the vacuum in the cavity, and hit the phosphor screen into glowing.

“We have found that a cathode with highly crystalline single-walled carbon nanotubes and an anode with the improved phosphor screen in our diode structure obtained no flicker field emission current and good brightness homogeneity,” Shimoi said.

Field emission electron sources catch scientists’ attention due to its ability to provide intense electron beams that are about a thousand times denser than conventional thermionic cathode (like filaments in an incandescent light bulb). That means field emission sources require much less power to operate and produce a much more directional and easily controllable stream of electrons.

In recent years, carbon nanotubes have emerged as a promising material of electron field emitters, owing to their nano-scale needle shape and extraordinary properties of chemical stability, thermal conductivity and mechanical strength.

Highly crystalline single-walled carbon nanotubes (HCSWCNT) have nearly zero defects in the carbon network on the surface, Shimoi explained. “The resistance of cathode electrode with highly crystalline single-walled carbon nanotube is very low. Thus, the new flat-panel device has smaller energy loss compared with other current lighting devices, which can be used to make energy-efficient cathodes that with low power consumption.”

“Many researchers have attempted to construct light sources with carbon nanotubes as field emitter,” Shimoi said. “But nobody has developed an equivalent and simpler lighting device.”

Considering the major step for device manufacture–the wet coating process is a low-cost but stable process to fabricate large-area and uniformly thin films, the flat-plane emission device has the potential to provide a new approach to lighting in people’s life style and reduce carbon dioxide emissions on the earth, Shimoi said.

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About American Institute of Physics
The journal Review of Scientific Instruments, which is produced by AIP Publishing, presents innovation in instrumentation and methods across disciplines. See: rsi.aip.org/

Printed Electronics & Nanomaterials Applications – How Close Are We?


Conductive nanomaterials for printed electronics applications

By Michael Berger. Copyright © Nanowerk

Printing Graphene Chips(Nanowerk Spotlight) The term printed electronics refers to the application of printing technologies for the fabrication of electronic circuits and devices, increasingly on flexible plastic or paper substrates. Printed electronics has its origins in conductive patterns printed as part of conventional electronics, forming flexible keyboards, antennas and so on.

 

Then came fully printed testers on batteries, electronic skin patches and other devices made entirely by printing, including batteries and displays (read more: “Printed electronics widens its scope”). Traditionally, electronic devices are mainly manufactured by photolithography, vacuum deposition, and electroless plating processes. In contrast to these multistaged, expensive, and wasteful methods, inkjet printing offers a rapid and cheap way of printing electrical circuits with commodity inkjet printers and off-the-shelf materials.

All inkjet technologies are based on digitally controlled generation and ejection of drops of liquid inks using one of two different modes of operation: continuous and drop-on-demand printing. Conductive inkjet ink is a multi-component system that contains a conducting material in a liquid vehicle (aqueous or organic) and various additives (such as rheology and surface tension modifiers, humectants, binders and defoamers) that enable optimal performance of the whole system, including the printing device and the substrate. The conductive material may be dispersed nanoparticles, a dissolved organometallic compound, or a conductive polymer.

A review article in Small (“Conductive Nanomaterials for Printed Electronics”) by Alexander Kamyshny and Shlomo Magdassi from The Hebrew University of Jerusalem, provides a state-of-the-art overview of the synthesis of metal nanoparticles; preparation of stable dispersions of metal nanoparticles, carbon nanotubes (CNTs) and graphene sheets; ink formulations based on these dispersions, sintering of metallic printed patterns for obtaining high electrical conductivity; and recent progress in the utilization of metal nanoparticles, carbon nanotubes, and graphene for the fabrication of various functional devices.

Requirements and challenges for printable dispersions of conductive nanomaterials The use of nanomaterials for the formulation of conductive inkjet inks poses several challenges:

  • – the nanoparticles in the ink should be stable against aggregation and precipitation in order to provide reproducible performance
  • – nanoparticle-based conductive inks should provide good electrical conductivity of printed patterns
  • – there is a need need for a post-printing process in order to sinter the nanoparticles for obtaining continuous metallic phase, with numerous percolation paths between metal particles within the printed patterns
  • – when using carbon nanotubes or graphene, the challenge is to prevent aggregation into CNT bundles or graphene layers.

In their article, Kamyshny and Magdassi address these challenges in great detail and then go on to describe preparation methods for metal, graphene, and CNT-based inkjet inks, which are suitable for printed electronics, and post-printing processing methods for obtaining high electrical conductivities.

        printed micro 3D structuresPrinting of a conductive 3D structure with the use of ink composed of an UV-curable emulsion and a dispersion of metal nanoparticles. Inset is a 3D profile of a 200 µm width lines composed of 1, 3, 6, 10, and 20 printed layers.(© The Royal Society of Chemistry)

Applications of conductive nanomaterials The authors also discuss several applications of conductive nanomaterials for the fabrication of printed electronic devices. This  includes fabrication and properties of transparent conductive electrodes, which are nowadays essential features for many optoelectronic devices, and inkjet-printed devices, such as RFID tags, light emitting devices, thin-film transistors (TFTs) and solar cells.

Transparent electrodes The market for transparent electrodes has grown tremendously due to wide proliferation of LCD displays, touch screens, thin-film solar cells, and light emitting devices. The most widely used material is indium tin oxide (ITO) with a market share of more than 97% of transparent conducting coatings. ITO coatings have some major drawbacks, though, and many efforts to find alternatives are based on nanomaterials – metal nanoparticles, metal nanowires, carbon nanotubes, and graphene – which can be printed directly on various substrates without etching processes.

RFID tags The main elements of an RFID (Radio Frequency Identification) tag are a silicon microchip and an antenna, which provide power to the tag and are responsible for communication with a reading device. Direct inkjet printing of antennas on plastic and paper substrates with the use of metal nanoparticles inks is a promising approach to the production of low-cost RFID tags.

Thin-film transistors Conductive nanomaterials are used to produce the conductive features on both inorganic and organic TFTs. See for instance our recent Nanowerk Spotlight on inkjet printing of graphene for flexible electronics or the report on inkjet printing of single-crystal films of organic semiconductors.

Light-emitting devices Light emitting devices (or electroluminescent devices, ELDs) are composed of a semiconductor layer placed between two electrodes, and emit light in response to electric current. LEDs to be used for lighting, require a highly conductive grid (“shunting lines”) for homogeneous distribution of current around the lighting device. These circuits can be fabricated on various substrates including plastic, by various printing processes using conductive nanomaterials.

Solar cells The first demonstration of inkjet-printed solar cells was already made in 2007 using fullerene-based ink. The results were discussed in this paper: “High Photovoltaic Performance of Inkjet Printed Polymer:Fullerene Blends”. In recent years, metal nanoparticles as well as nanowires and CNTs have been also used in solar cells fabrication as well.

Concluding their review, the authors note that, in spite of the remarkable scientific progress in preparation processes and applications of conductive nanomaterials, they are still not widely used by the industry in significant quantities:

“The current high price of commercially available inks, which are based mainly on the high cost silver, impedes their wide use for large area printed electronics. Therefore, research should be focused on the development of new nanomaterials and ink formulations based on low cost metals with high electrical conductivity such as copper, nickel, and aluminum.”

They also note that in recent years, many scientific activities have been focusing on graphene and that we can expect future developments in printed electronics that will combine CNTs with graphene. Successive utilization of graphene for printed electronics requires ink formulations with high graphene loading, which are stable against flakes aggregation.

One final thought is the application of conductive nanomaterials in 3D printing of conductive patterns which opens some important perspectives for materials science. Although, this field is at its very early stages of research and development, and the search for new nanomaterials as well as suitable 3D fabrication tools based on wet deposition, it is a stimulating challenge for materials scientists.

Read more: Conductive nanomaterials for printed electronics applications http://www.nanowerk.com/spotlight/spotid=34566.php#ixzz2uXlGfxfi Follow us: @nanowerk on Twitter

Quantum Dot Market to Grow from $108.4 Million (2013) to $3.4 BILLION by 2020


Steep Growth graph 011514

Title: Quantum Dots Market by Product (QD Displays, Lasers, Medical Devices, Solar Cells, Chip, Sensor), Application (Healthcare, Optoelectronics, Sustainable Energy), Material (Cadmium Selenide, Sulfide, Telluride), and Geography – Forecast & Analysis (2013 – 2020).

Quantum Dots (QD) are the types of semiconductor nanoparticles, which find their usage in multiple applications like healthcare, electronics, and so on. The current market of QD is at the pre-commercialized stage; most of the researchers are working on the “application aspects” of the QD technology, and deriving the products based on QD.

Researchers have studied the quantum dots in transistors, solar cells, LEDs, and diode lasers. They have also investigated quantum dots as agents for medical imaging and, soon, the QDs will be used as ‘qubits’ in quantum computing.

This report deals with all the driving factors, restraints, and opportunities for the QD technology market, which are helpful in identifying the trends and key success factors for the industry. The report also profiles companies that are active in the field of QD technology. It also highlights the winning imperatives and burning issues pertaining to the QD technology industry.

The Quantum Dots market is expected to grow from the $108.41 million that it accounts for, currently, in 2013 to $3,414.54 million in 2020, at a CAGR of 71.13% from 2014 to 2020. Optoelectronics application is expected to be the major market share holder, with an expected revenue generation of $2,458.47 million in 2020.

Quantum Dots: Samsung to Reveal NEW QLED at Annual CES Conference in Las Vegas: January 7 – 10


6 January 2014
quantum d 1

The picture on the left is from a backlight unit using quantum dots, while the one on the right is from a regular backlight unit. Notice the difference in color quality. – See more at: http://www.businesskorea.co.kr/article/2834/quantum-dots-samsung-unveil-secret-weapon-2014-international-ces#sthash.bvbNOAlm.dpuf

 

Samsung is reportedly planning to unveil its secret weapon, the V1 Bomb, a high-definition TV called Quantum-dot LED TV (QLED TV) at the 2014 International CES, the world’s biggest electronics show in Las Vegas in January.

According to an industry source on January 3, Samsung Electronics is considering showcasing the Quantum-dot display of QLED TV in the upcoming 2014 International CES.  QLED TV is a TV that is designed to use self-luminous quantum dots in nanoscale crystals of semiconductor chips that enable the display of colors without any more parts. The model that is expected to be introduced is a type of QLED that uses Quantum Dot Enhancement Film (QDEF) technology instead of a traditional backlighting unit.  In that sense it is by definition not a true QLED, but its viability as a commercial product is immense, since manufacturing a large screen display using QLED technology is much easier then using an existing Organic Light-Emitting Diode, or OLED.

In 2011, Samsung succeeded in developing the world’s first full-color display using quantum dots.  LG Electronics followed suit by forming a Memorandum of Understanding with US nanotechnology company QD Vision to build its own QLED TV. In the first half of last year, 3M and Nanosis introduced a prototype of QDEF targeted at LCD manufacturers.     Japanese manufacturers such as Sony and Panasonic have suspended competition with Samsung and LG’s OLED products, and have reportedly been concentrating their efforts on developing QLED technology to be used in UHD TV.  Taiwan’s LCD manufacturer AU Optronics is also said to be working on its own color-enhanced QLED using QDEF.

A source close to the electronics manufacturing industry said, “3M, the primary developer of QDEF, is right now supplying 85-inch QDEF products to LCD makers.”  As of 3Q and 4Q of 2012, there were several manufacturers in the 85-inch LCD TV market, of which Samsung owned a 72 percent share.  Considering Samsung’s lofty position, it is highly likely that it will introduce a prototype product at the 2014 CES.

On whether or not Samsung will unveil its QLED TV at 2014 CES, another source said, “CES is not necessarily an exhibit for finished products.  Rather, it is a platform for manufacturers to showcase their latest technologies.  Thus it is possible and likely that we will see Samsung’s QLED at the show.”

– See more at: http://www.businesskorea.co.kr/article/2834/quantum-dots-samsung-unveil-secret-weapon-2014-international-ces#sthash.bvbNOAlm.dpuf

Quantum Dots Poised to Make IMPACT on LED Back-Lit LCD’s


What technology is in YOUR TV (Display) Screen?!

qdot-images-3.jpg

Ken Marrin, LED Magazine

Quantum dot (QD) technology has promised to enhance LED usage, making LCD TV images more vivid and improving efficacy in warm-CCT, high-CRI solid-state lighting (SSL). Thus far, however, cost, reliability, and lifetime issues have prevented broad commercial deployment. But the technology has progressed to the point that the TV application, with relatively shorter usage hours compared to general lighting, can adopt the technology.

Due to their high resolution, low cost, and thin form-factors, LED-backlit LCDs have become the standard for mobile devices and TVs, although color performance has lagged. (For more details on how LCDs and backlights work, see sidebar at end.) Displays on popular backlit LCD tablets can only express about 20% of the color a human eye can see, while LCD HDTVs can express only about 35%. To achieve more vivid, realistic color, display manufacturers have developed a variety of new technologies such as discrete RGB LED backlights, yttrium aluminum garnet (YAG) enhanced with red phosphor, and organic LEDs (OLEDs). All are beset with cost, scalability, and durability issues that have hampered widespread deployment.

FIG. 1. For TV applications, QD Vision supplies quantum dots enclosed in an optic element that is coupled to the backlight unit.
FIG. 1.

One of the most promising new color enhancement technologies for backlit LCDs is QDs, a nanocrystal material that can be tuned to emit an optimized narrow spectrum of light. The unique semiconductor and optical properties of quantum dots make them attractive for a broad range of applications, from SSL, silicon photovoltaic cells, and quantum computing to cellular imaging and organic dye replacement. Due to the high production volumes and ease of integration with existing manufacturing processes, LCD suppliers seem to have taken a particular interest in QDs. By augmenting their backlight units (BLUs) with QDs, LCD manufacturers are able to create vivid displays that can exceed 55% of the spectrum a human eye can detect.

Why quantum dots?

Where vivid color and high efficiency are the objectives, the ideal white light is one that can be tuned to generate lots of visible energy narrowly focused on the primary red, green, and blue wavelengths used by the subpixel filters while producing very little light between. QDs do just that. The tiny nanocrystals, smaller than a virus, emit narrowband light when excited by a photon source.

Unlike conventional phosphor technologies like YAG, which emit with a fixed spectrum, QDs can be fabricated to convert light to nearly any color in the visible spectrum by simply varying the size of the dots. Size and bandgap energy are inversely related, so as the size of the QD decreases, emission frequencies increase, resulting in a color shift from red (low energy) to blue (high energy) in the light emitted. Lifetime fluorescence is also determined by the size of the QD, with larger dots showing a longer lifetime.

By carefully controlling the size of the crystals as they are synthesized, the spectral peak output can be set to within 2 nm of nearly any visible wavelength. Such control enables QDs to be tuned so the backlight spectrum matches the color filters, thereby facilitating displays that are brighter and more efficient, and produce truly vibrant colors.

Integrating QDs with the BLU

Quantum dot approaches are similar to phosphor technologies in the way they attempt to engineer the white light spectrum. As with YAG, a blue GaN LED provides the source light. QDs then downconvert a portion of the blue light into narrowband red and green spectrum, thereby achieving a white light that is rich in red, green, and blue and matched to the subpixel filters. QDs can be tuned (by varying the size) to emit at any wavelength longer than the source wavelength with very high efficiency (over 90% quantum yield under ideal conditions) and with very narrow spectral distribution — just 30–40 nm full width at half maximum (FWHM). This high spectral efficiency in turn reduces display power consumption by 20% compared to other high-gamut color-enhancement techniques — a key factor in meeting Energy Star requirements in TVs or extending battery life in portable devices where displays often consume 40% of the power.

As with YAG, QD backlight technology is easy to integrate with existing LCD manufacturing processes. QD upgrades require no line retooling or process changes. So manufacturers who have invested billions in LCD plants and equipment can quickly deploy QD-enhanced LCD panels that offer the color and efficiency of the best OLEDs at a fraction of the cost.

FIG. 2. Pacific Light Technologies plans to offers white LEDs with the red quantum dots deposited directly on the LED along with the other phosphors.
FIG. 2.

3M, for example, is now using QDs supplied by Nanosys, Inc. to offer a quantum-dot enhancement film (QDEF) a thin, optically-clear sheet with red and green dots that replaces the existing diffuser film in the reflective cavity of an LCD backlight. This packaging, explains 3M marketing development manager Art Lathrop, “not only simplifies integration and protects the dots against flux but boosts efficiency by recycling light emitted in the wrong direction.”

3M has initially focused on mobile displays where the industry has put more emphasis on premium quality and displays sell for a relatively high price per square meter. Larger displays are not only more price sensitive, Lathrop added, but also heavier users of QDs in the film implementation. When an application grows linearly (long strips of displays, for example), the QD film and the number of dots used in the film grows linearly as well, so cost is not a problem. However, when the application grows more by area than length — as in a TV display — then the number of QDs required for the film grows exponentially with display size, and the cost of QDs becomes a significant factor. Lathrop expects this issue to abate as the raw QD materials get cheaper and packaging/manufacturing (inexpensive film vs. glass, for instance) becomes the driver of overall QD cost. Until then, 3M will focus on smaller displays with lower raw material costs such as consumer mobile devices.

Drop-in QD technology

QD Vision also provides a drop-in technology called Color IQ, though instead of packaging the QDs as a film, QD Vision employs a glass tube that mounts on the edge of the display (Fig. 1). Unlike the 3M film, which scales geometrically, the rail solution scales linearly, making it more effective for larger displays. “With an edge solution like Color IQ,” said QD Vision CTO Seth Coe-Sullivan, “we utilize about one-hundredth of the QD materials relative to a film solution of the same screen area. This is why you see 3M launching in the Kindle with a screen area of one-sixtieth of a square meter, while we are in big-screen Sony TVs.”

Nanosys CEO Jason Hartlove concedes that the film solution is a heavier dot user but puts the differential at about 5x. The shorter optical path in the edge solution, he argues, requires a much higher dot density (less opportunity for recycling) and is also susceptible to aggregation and quenching, which reduces the dot’s light output and requires additional LEDs to get the same brightness.

FIG. 3. Pacific Light Technologies says that its technology using red quantum dots in place of phosphor delivers 30% more lumen output.
FIG. 3.

Pacific Light Technologies got its start in nanotechnology developing QDs for the solar industry, where the dots are used to convert solar energy into a low-energy format that can be utilized more efficiently by solar panels. From there, the company branched off into SSL, using QDs to create warmer lighting solutions. More recently, the company has attracted interest from display makers. Their key differentiator, according to vice president of marketing Julian Osinski, is the ability to fabricate dots directly onto blue LEDs, eliminating the need for a separate QD subassembly (Fig. 2). “A display requiring coverage over the full surface can be on the order of 10,000x the surface area of the LED chips used to illuminate the display,” said Osinski, “and since the amount of QDs required scales with surface area, that means 10,000 times less QD material is required for on-chip use compared to off-chip.”

Pacific Light uses the same process for adding dots to LEDs that manufacturers use to add phosphor. The QDs are synthesized in a reactor vessel, separated out, mixed into a silicone, and then applied to the chip. “One nice advantage,” noted Osinski, “is that unlike phosphors, there is no settling of QD particles, resulting in more stable color points during manufacturing.” Pacific Light Technologies is currently shipping red dots, with plans for green dots in the future.

Quantum dot reliability

The useful life of the QDs is a complex issue heavily dependent on the application and the operating conditions. Fundamentally, what kills dots the fastest is oxidation. Beyond that, assuming that the dots are very well protected from oxygen, they also deteriorate from being used (like most emitters), and that deterioration accelerates with elevated heat and flux, particularly flux. Temperature at the film is about 40°C vs. 90°C at the edge, and 140°C at the LED, said Hartlove of Nanosys. Flux is 25 MW/cm at the film, 1–10W/cm at the edge, and from tens to hundreds of watts per centimeter at the LED — five orders of magnitude from the film to the LED.

3M’s testing, said Lathrop, shows that in most consumer applications QDEFs last for 20,000 to 30,000 hours of operation before luminance drops by 15%. A larger drop will start to result in a noticeable color shift (blue is not impacted). 3M’s next-generation product is targeting twice that lifetime, not because display makers are looking for 60,000+ hours but because they want to use them in hotter displays (all-in-one PCs or specialty displays, for example).

QD Vision’s edge solution, which encapsulates the dots in a glass tube, provides an excellent barrier to oxygen, as well as other advantages such as lower volume utilization, low-tech barrier materials, and excellent color uniformity (no blue light leakage). “Our edge implementation also presents unique challenges,” explained Coe-Sullivan. Color IQ sits closer to the LED backlight than a film, so the dots must withstand higher heat (100°C) and flux (100x that of a film). Nonetheless, Coe-Sullivan claims to have overcome those challenges and rates the Color IQ lifetime at between 30,000–50,000 hours, essentially the same as present-day LEDs.

FIG. 4. Sony's Ultra HD TVs use quantum-dot technology from QD Vision to create more vivid colors, which Sony brands
FIG. 4.

Pacific Light Technologies’ approach to mounting dots directly on the LED may offer the most significant potential cost and performance advantages of all (Fig. 3) but also the greatest challenges with regard to reliability. In addition to higher temperatures, flux in particular can be 50x that of an edge solution. “In general,” noted Osinski, “white-light LED lifetimes are limited by the silicon-phosphor combination on the chip more than the chip itself, and that remains the same with QDs, where silicone yellowing also contributes to aging blue LEDs.” Reliabilities are still being established because they require very long test times, but Pacific Light claims to have already demonstrated operation over thousands of hours.

OLED

One of the chief competitive technologies to QDs where color quality is of primary importance is OLED, which emits light directly and requires no backlight or LCD filter. In addition to excellent color gamut comparable to QDs, OLED displays feature faster response times and refresh rates, improved brightness, a greater contrast ratio (both dynamic range and static, measured in purely dark conditions), a wider viewing angle than LCD implementations (with or without QD augmentation), and the ability to display true blacks.

Perhaps the biggest technical problem for OLEDs is the limited lifetime of the organic materials, primarily for the blue OLEDs. Blue OLEDs historically have had a lifetime of around 14,000 hours to half original brightness (five years at 8 hours a day) when used for flat-panel displays. Red and green OLEDs offer 2–3x that lifetime. The faster degradation of blue OLEDs relative to red and green creates color balance challenges, requiring either additional control circuitry, or optimization of the red, green, and blue subpixel sizes in order to equalize color balance at full luminance over the lifetime of the display. A blue subpixel, for example, may need to be 100% larger than the green subpixel, whereas the red subpixel may need to be 10% smaller than the green.

High cost has also hampered the widespread use of OLEDs in larger mass-market displays. Eliminating the backlight and LCD filter provides significant cost savings and allows for a thinner display, but the fabrication of the OLED substrate is presently more costly than that of a thin-film transistor LCD. Down the road, the ability to fabricate OLEDs on flexible plastic substrates and the utilization of processes like roll-to-roll vapor-deposition and transfer printing will offer potential cost advantages. For now, though, large-screen applications require low-temperature polysilicon backplanes that cannot currently be used on large-area glass substrates. As a result, large OLED displays are limited to relatively high-end applications, with OLED TVs from LG and Samsung selling in the $10,000 range. On the other hand, Sony uses QD Vision’s technology, branding it Triluminos, in its 4000-pixel Ultra HD LCD TVs that start at about $3500 (Fig. 4). But Sony has also included Triluminos technology in some higher-end standard HDTV sets such as a 55-in. model that sells for around $2000.

Electroluminescent QDs

Even as OLED strives for economies of scale and process improvements that will bring costs down, QD makers like QD Vision are already working on the next generation of technology — electroluminescent QDs that will combine the customizable, saturated, stable color and low-voltage performance of inorganic LEDs with the solution processability of polymers. The new technology, Coe-Sullivan explains, will provide a reliable, energy-efficient, highly tunable color solution for displays and lighting that is less costly to manufacture and that can employ ultrathin, transparent, or flexible substrates.

Quantum-dot light-emitting diodes (QLEDs) are electroluminescent colloidal quantum dots that generate light when excited electrically. Like OLEDs, QLEDs require no backlight or LCD filter. QD Vision claims that its printable thin-film QLEDs match or exceed NSTC color standards for displays without the need for color filters. The excellent color performance of QLEDs ultimately translates into a 30–40% luminance efficiency advantage over OLEDs (at the same color point), which require lossy color filtering to achieve a similar color performance. QLEDs also feature a lower operating voltage, exhibiting turn-on voltages at the bandgap voltage of the material. This gives QLEDs the potential to be more than twice as power efficient as OLEDs at the same color purity.

To reduce cost for QLED-based, full-color, active-matrix displays and lighting devices, QD Vision is developing large-area quantum-dot printing techniques that utilize ultrathin flexible substrates. Today’s LCDs and LED chips are fabricated on glass and crystalline substrates, making them inherently expensive and fragile for mobile and large-area applications. QLEDs, by contrast, are only a couple hundred nanometers thick, making them virtually transparent and flexible, and highly suitable for integration onto plastic or metal foil substrates as well as other surfaces.

QLEDs are still in the early development stages, yielding only 10,000 hours at low brightness, but in theory are a more stable light-emitting material than organic dyes. Meanwhile, the company is already offering high-quality electroluminescent-grade QD materials suitable for certain products that require precise color solutions in an ultraslim form factor. Among these are monochrome visible and infrared displays, and lighting devices for machine and night vision applications.

Nanosys’ Hartlove agreed that the QLEDs are the way of the future. “When emissive pixels will overtake LCDs we cannot say. LCDs get better every day.” Within ten years, however, he expects the manufacturing and production advantages of QLEDs (solution chemistry and roll-printed emitters) to overtake GaN substrates and wafer-based processing — and not just for displays but also general lighting. Right now, the focus is on the ability of QDs to outperform phosphors in the color arena, but eventually the properties of the raw materials will fade in significance, and it will come down to manufacturing, where the ability to print narrowband emissive pixels on thin films in high volume will produce high-quality color inexpensively — without the need for color management.

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Backlight enhancement

Liquid-crystal displays (LCDs) combine a light source (the backlight unit, or BLU) with a liquid-crystal module (LCM). The BLU provides a uniform white sheet of light behind the LCM. The LCM contains millions of pixels, each of which is split into red, green, and blue subpixels. By controlling the amount of time each subpixel filter is open (allowing light to pass through it) and making use of the human eye’s persistence of vision, the LCD can display any color that can be rendered from a combination of red, green, and blue at each pixel location. The color filter on each subpixel separates its component color from the white light of the BLU. For example, the red color filter on the red subpixels blocks the green and blue light.

The fidelity of each color is a function of the quality of light in the BLU and the color filters. The narrower the filters, the narrower the backlight color spectrum (for the desired peak red, blue, and green colors), and the closer the color spectrum is matched to the filters, the higher the color quality. Because making perfect color filters is impractical from a cost and brightness perspective (narrow filters attenuate out-of-band photons and reduce brightness), display makers have instead focused their efforts on improving the BLU.

The problem with standard BLUs is that the LEDs used to create the backlight produce a broad spectrum of light that cannot be used efficiently by the LCD. Most white LEDs are created by coating blue LEDs made of indium gallium nitride (InGaN) with an yttrium aluminum garnet (YAG) phosphor. These two-color YAG white LEDs produce a spectrum rich in blue wavelengths with a broad yellow component, but the greens vary from cyan through lime, and the reds vary from orange to deep red. Because the filters can’t stop these in-between colors, the result is poor color saturation.

Red-emitting phosphor can be added to boost color performance, but red phosphors suffer from poor conversion efficiency, wasting much of their power-generating spectrum like infrared that is not visible to the human eye. Like the yellow phosphors, red phosphors have a relatively wide full width at half maximum (FWHM) — a characterization of the width of the spectrum at which emitted radiometric power has dropped by half — so they cannot be precisely tuned to match either existing color filters or the manufacturers’ peak color specifications. So the resulting white light, while offering a richer spectrum, still incurs substantial light and efficiency losses

Quantum Dots Enter Mainstream Mobile Device Market


Last month, Amazon released Kindle Fire HDX 7 — the first ever mobile device to feature a quantum-dot-enhanced display.

The 7″ display includes a Quantum Dot Enhancement Film (QDEF) produced by 3M in collaboration with Nanosys, Inc. Compared to the traditional LED-LCD display, the QDEF essentially replaces the YAG phosphor of the white LED backlight and functions as a high-efficiency photoluminescent emitter. The ODEF includes quantum dots of different sizes, which would emit different colors when excited due to quantum confinement effect. More detail of the QDEF can be found via the link below.

http://www.nanosysinc.com/what-we-do/display-backlighting/qdef-how-does-it-work/

It is noted that the quantum-dot-enhanced display of Kindle Fire HDX 7 does not utilize the electroluminescent property of quantum dots, and thus is not actually a quantum dot light emitting diode (QLED). Nevertheless, it could signal the beginning of the mass commercialization of quantum dots technology in consumer markets.

And the very “best” of todays technologies? According to Displaymate, quote:

“The very best of today’s display technologies? The Quantum Dots displays used in the Kindle Fire HDX 7 according to the report.

Quantum Dots are almost magical because they use Quantum Physics to produce highly saturated primary colors for LCDs that are similar to those produced by OLED displays. They not only significantly increase the size of the Color Gamut by 40-50 percent but also improve the power efficiency by an additional 15-20 percent. Instead of using White LEDs (which have yellow phosphors) that produce a broad light spectrum that makes it hard to efficiently produce saturated colors, Quantum Dots directly convert the light from Blue LEDs into highly saturated primary colors for LCDs. You can see the remarkable difference in their light spectra in Figure 4. Quantum Dots are going to revolutionize LCDs for the next 5+ years.”

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How does QDEF work?

Nanosys QDEF™ enables deep color and high efficiency by providing displays with an ideal light source. How does it do that?

Each sheet of QDEF contains trillions of tiny (by tiny we mean: a bit bigger than a water molecule but smaller than a virus in size) nanoscrystal phosphors, called “Quantum Dots .” Not found naturally occurring anywhere on Earth, these “dots” can be tuned, by changing their size, to emit light at just the right wavelengths for our displays and do so very efficiently.

Unlike conventional phosphor technologies such as YAG that emit with a fixed spectrum, quantum dots can actually convert light to nearly any color in the visible spectrum. Pumped with a blue source, such as the GaN LED, they can be made to emit at any wavelength beyond the pump source wavelength with very high efficiency (over 90% quantum yield) and with very narrow spectral distribution (only 30 – 40nm FWHM.) The real magic of quantum dots is in the ability to tune the color output of the dots, by carefully controlling the size of the crystals as they are synthesized so that their spectral peak output can be controlled within 2 nanometers to nearly any visible wavelength.

For the first time, display designers will have the ability to tune and match the backlight spectrum to the color filters. This means displays that are brighter, more efficient, and produce truly vibrant colors.

How does it all come together?

Engineering the quantum dots to precise display industry specifications isn’t enough to revolutionize the way LCDs are experienced on its own. The dots need to be easily integrated into current manufacturing operations with minimal impact on display system design if they are to be widely adopted. To do this, Nanosys spent a lot of time working with major display manufacturers to get the packaging just right so that it would be a simple, drop-in product that did not require any line retooling or process changes. The end result is called Quantum Dot Enhancement Film or QDEF.

Designed as a replacement for the an existing film in LCD backlights called the diffuser, QDEF combines red and green emitting quantum dots in a thin, optically clear sheet that emits white light when stimulated by blue (some of that blue is allowed to pass through to make the B in RGB at the LCM of course). So manufacturers who’ve invested billions in plant and equipment for LCD production can simply slip this sheet into their process, change their ‘white’ LEDs to blue (the same LEDs but without the phosphor) and start producing LCD panels with the colors and efficiencies of the best OLEDs, at a fraction of the cost and current industrial scale.

Nanosys is currently shipping production samples to display manufacturers and is on track to begin producing at commercial volumes fall of 2013.

Reactor for Bulk Manufacturing of Core-Shell Quantum Dot Nanoparticles


Enables Large-Scale Production of Precision Quantum Dots for Medical Imaging, LEDs and Solar Cells

mix-id328072.jpgThis multi-variable reactor facilitates the manufacturing of high-precision, core-shell quantum dots – nanoparticles made from semiconductive materials that display unique optical and electrical properties. Quantum dots have applications in computing, photovoltaic devices (solar panels), light emitting diodes (LEDs) and medical imaging equipment.

 

By modifying or “tuning” the precise size and quality of quantum dots, scientists can control the wavelength (bandgap) of light emitted by LEDs, and can select the properties for various other applications, such as fluorescence-based diagnostics and cell staining in medical imaging. Quantum dots are currently manufactured using batch methods, which under hydrothermal conditions, are time-consuming and subject to batch-to-batch variation in the desired properties. Detailed tuning of quantum dots to precise optical properties can be difficult using existing technology. Researchers at the University of Florida have developed a hydrothermal reactor that offers high-precision tuning of quantum dots for bulk production. The reactor enhances reliability, precision, uniformity and throughput during large-scale quantum dot manufacturing, and could help capture a significant portion of the global quantum dots market, which is expected to reach $670 million by 2015.

 

To Read More Go To The Link Here:

http://technologylicensing.research.ufl.edu/technologies/14105/reactor-for-bulk-manufacturing-of-core-shell-quantum-dot-nanoparticles

 

Inkjet Print Process Devised for Quantum Dot Organic LEDs


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  *** Original Post by Alan Kotok from “Science and Enterprise. ***

Engineers at University of Louisville in Kentucky developed a process for making organic light-emitting diodes (OLEDs) with quantum dots and applied with inkjet printing, a common manufacturing technology. The findings of the research team led by Louisville engineering professor Delaina Amos will be presented next week at the Optical Society’s Conference on Lasers and Electro-Optics in San Jose, California.

OLEDs are solid-state devices made with thin films of organic molecules that generate light when an electric current passes through. Displays made with OLEDs can be made much thinner and flexible, and use less power than LED or liquid-crystal displays found in conventional flat-screen televisions or computer monitors. However, widespread manufacturing of OLEDs has been held back because of the cost of materials and their expensive production processes.

The Louisville team aims to create an OLED manufacturing technique with inkjet printing, an established manufacturing process widely used in commercial settings. Their methods use quantum dots made of cadmium selenide, an inorganic material, forming a hybrid type of OLED. Quantum dots are nanoscale semiconductor crystals, which have among other properties photoelectric effects.

These synthesized quantum-dot OLEDs, says Amos, are more efficient than earlier OLEDs and can present a wider spectrum of colors. She adds that they are also less expensive to produce and more environmentally friendly, using low-toxicity materials.

Amos and colleagues demonstrated their technology using cadmium selenide quantum dots in a solution applied with an inkjet printer. The OLEDs are applied in layers, with interfaces between the layers designed to improve the efficiency with which electrons are transferred through the device.

The demonstrations so far created small-scale (1-inch by 1-inch square) OLED devices, but Amos says they can be scaled up to 6 by 6 inches or larger within the next few months. “Ultimately,” notes Amos, “we want to have low cost, low toxicity, and the ability to make flexible devices.”

Read more:

Samsung licenses quantum dot LED IP from Evident Technologies: Where are They Now?


*** GNT Team Note: This announcement was significant now almost 2 and a-half years ago. But Team GNT wants to know .. “Where are they now?” 

 

201306047919620May 6, 2011 Evident Technologies Corporation and Samsung Electronics Co. Ltd entered into a comprehensive patent licensing and purchasing agreement for Evident’s quantum dot LED technology. This agreement grants Samsung worldwide access to Evident’s patent portfolio for all products related to quantum dot LEDs from manufacture of the quantum dot nanomaterials to final LED production.

“We are excited that Samsung, the leader in consumer electronics, has licensed our quantum dot technology,” said Dr. Clint Ballinger, CEO of Evident Technologies. “We already enjoy a terrific working relationship and look forward to the future of this technology.”

Quantum dots are nanometer-sized semiconductor crystals that have great commercial promise in electronic applications from solar energy conversion to thermoelectrics to LEDs. Evident commercialized quantum dot LEDs with products launched in 2007.

Evident Technologies is a nanotechnology company specializing in the creation of semiconductor quantum dots. Learn more at http://www.evidenttech.com/.