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QD Brightness U of Illinois 100515 id41509Researchers at the University of Illinois at Urbana-Champaign have introduced a new class of light-emitting quantum dots (QDs) with tunable and equalized fluorescence brightness across a broad range of colors. This results in more accurate measurements of molecules in diseased tissue and improved quantitative imaging capabilities.
“In this work, we have made two major advances–the ability to precisely control the brightness of light-emitting particles called quantum dots, and the ability to make multiple colors equal in brightness,” explained Andrew M. Smith, an assistant professor of bioengineering at Illinois. “Previously light emission had an unknown correspondence with molecule number. Now it can be precisely tuned and calibrated to accurately count specific molecules. This will be particularly useful for understanding complex processes in neurons and cancer cells to help us unravel disease mechanisms, and for characterizing cells from diseased tissue of patients.”
Quantum Dots
Left: Conventional fluorescent materials like quantum dots and dyes have mismatched brightness between different colors. When these materials are administered to a tumor (shown below) to measure molecular concentrations, the signals are dominated by the brighter fluorophores. Right: New brightness-equalized quantum dots that have equal fluorescence brightness for different colors. When these are administered to tumors, the signals are evenly matched, allowing measurement of many molecules at the same time. (Image: University of Illinois)
“Fluorescent dyes have been used to label molecules in cells and tissues for nearly a century, and have molded our understanding of cellular structures and protein function. But it has always been challenging to extract quantitative information because the amount of light emitted from a single dye is unstable and often unpredictable. Also the brightness varies drastically between different colors, which complicates the use of multiple dye colors at the same time. These attributes obscure correlations between measured light intensity and concentrations of molecules,” stated Sung Jun Lim, a postdoctoral fellow and first author of the paper, “Brightness-Equalized Quantum Dots,” published this week in Nature Communications.
According to the researchers, these new materials will be especially important for imaging in complex tissues and living organisms where there is a major need for quantitative imaging tools, and can provide a consistent and tunable number of photons per tagged biomolecule. They are also expected to be used for precise color matching in light-emitting devices and displays, and for photon-on-demand encryption applications. The same principles should be applicable across a wide range of semiconducting materials.
“The capacity to independently tune the QD fluorescence brightness and color has never before been possible, and these BE-QDs now provide this capability,” said Lim. “We have developed new materials-engineering principles that we anticipate will provide a diverse range of new optical capabilities, allow quantitative multicolor imaging in biological tissue, and improve color tuning in light-emitting devices. In addition, BE-QDs maintain their equal brightness over time while whereas conventional QDs with mismatched brightness become further mismatched over time.

These attributes should lead to new LEDs and display devices not only with precisely matched colors–better color accuracy and brightness–but also with improved performance lifetime and improved ease of manufacturing.” QDs are already in use in display devices (e.g. Amazon Kindle and a new Samsung TV).

Source: University of Illinois College of Engineering

U of Illinois QD 150807131233_1_540x360 Large-area integration of quantum dots, photonic crystals produce brighter and more efficient light.

Recently, quantum dots (QDs)–nano-sized semiconductor particles that produce bright, sharp, color light–have moved from the research lab into commercial products like high-end TVs, e-readers, laptops, and even some LED lighting. However, QDs are expensive to make so there’s a push to improve their performance and efficiency, while lowering their fabrication costs.

Researchers from the University of Illinois at Urbana-Champaign have produced some promising results toward that goal, developing a new method to extract more efficient and polarized light from quantum dots (QDs) over a large-scale area. Their method, which combines QD and photonic crystal technology, could lead to brighter and more efficient mobile phone, tablet, and computer displays, as well as enhanced LED lighting.

With funding from the Dow Chemical Company, the research team, led by Electrical & Computer Engineering (ECE) Professor Brian Cunningham, Chemistry Professor Ralph Nuzzo, and Mechanical Science & Engineering Professor Andrew Alleyne, embedded QDs in novel polymer materials that retain strong quantum efficiency. They then used electrohydrodynamic jet (e-jet) printing technology to precisely print the QD-embedded polymers onto photonic crystal structures. This precision eliminates wasted QDs, which are expensive to make.

These photonic crystals limit the direction that the QD-generated light is emitted, meaning they produce polarized light, which is more intense than normal QD light output.

According to Gloria See, an ECE graduate student and lead author of the research reported in Applied Physics Letters, their replica molded photonic crystals could someday lead to brighter, less expensive, and more efficient displays. “Since screens consume large amounts of energy in devices like laptops, phones, and tablets, our approach could have a huge impact on energy consumption and battery life,” she noted.

“If you start with polarized light, then you double your optical efficiency,” See explained. “If you put the photonic-crystal-enhanced quantum dot into a device like a phone or computer, then the battery will last much longer because the display would only draw half as much power as conventional displays.”

To demonstrate the technology, See fabricated a novel 1mm device (aka Robot Man) made of yellow photonic-crystal-enhanced QDs. The device is made of thousands of quantum dots, each measuring about six nanometers.

“We made a tiny device, but the process can easily be scaled up to large flexible plastic sheets,” See said. “We make one expensive ‘master’ molding template that must be designed very precisely, but we can use the template to produce thousands of replicas very quickly and cheaply.”


Story Source:

The above post is reprinted from materials provided by University of Illinois College of Engineering. The original item was written by Laura Schmitt. Note: Materials may be edited for content and length.


Journal Reference:

  1. Gloria G. See, Lu Xu, Erick Sutanto, Andrew G. Alleyne, Ralph G. Nuzzo, Brian T. Cunningham. Polarized quantum dot emission in electrohydrodynamic jet printed photonic crystals. Applied Physics Letters, 2015; 107 (5): 051101 DOI: 10.1063/1.4927648

Yole Développement says revenues “will exceed phosphors by 2020” as adoption

into LCD TVs rivals OLED quality.

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Quantum dots’ virtual adoption cycle, according to Yole Développement

 

Yole Développement (Yole), the Lyon, France-based market research and strategic

consulting company, has published its new LED down converters technology and market

report, entitled Phosphors & Quantum Dots 2015: LED Down Converters for Lighting & Displays.

It presents a detailed review of the industry, especially the impact of the development of

quantum dots on the display and conventional phosphors industry. Yole asks, are quantum dots

now a serious competitor to OLED-based technologies – and its conclusion is: quantum dots

are finally ready for prime time and will exceed traditional phosphor revenue by 2020 by

allowing LCD to compete with OLED in the race for the next generation of displays.”

After the lukewarm reception of 3D and 4K screens, Yole comments that the display

industry needs a “new and disruptive experience improvement” to bring consumers back

to the stores: “image quality perception increases significantly when color gamut and

dynamic contrast ratio are improved.” Yole also notes that “Leading movie studios,

content providers, distributors and display makers have together formed the UHD Alliance

to promote those features.”

Dr Eric Virey, Senior Analyst, LEDs at Yole, commented, “OLED was believed to be

the technology of choice for this next generation of displays. But production challenges

have delayed the availability of affordable OLED TVs. LCD TVs with LED backlights

based on quantum dot down-converters can deliver performance close to, or even

better than OLED in some respects, and at a lower cost.”

 

QD-LCD ‘could pull ahead’ of OLED display

Until OLEDs are ready, says Yole, “QD-LCD technology will have a unique window of

opportunity to try to close enough of the performance gap such that the majority of

consumers will not be able to perceive the difference between the two technologies

so price would become the driving factor in the purchasing decision.” Under this scenario,

the analyst believes that QD-LCD could establish itself as the dominant technology while

struggling OLEDs “would be cornered into the high end of the market.”

Yole acknowledges that OLED-based displays potentially offer more opportunities for

differentiation but the analyst notes, “OLED proponents need to invest massively and

still have to resolve manufacturing yield issues. For tier-2 LCD panel makers who

cannot invest in OLED, Quantum Dots offer an opportunity to boost LCD performance

without imposing additional CAPEX on their fabs.” At this year’s Consumer Electronics

show, as optics.org reported, no fewer than seven leading TV OEMs including

Samsung and LG demonstrated QD-LCD TVs.

 

With tunable and narrowband emissions, QDs offer design flexibility to developers

of new displays. But more is needed to enable massive adoption, including the d

evelopment of cadmium-free formulations. Cole cautions that “traditional phosphors

still have to say their last word”. If PFS could further improve in term of stability and decay

time and a narrow-band green composition was to emerge, traditional phosphors could

also be part of the battle against OLED, Yole concludes.

 

Yole’s analysis Phosphors & Quantum Dots 2015: LED Down-converters for Lighting & Displays

presents an overview of the quantum dot LED market for display and lighting applications

including quantum dot manufacturing, benefits and drawbacks, quantum dots LCD versus

OLED and detailed market forecast. For more information about this report and other

LED technology & market analysis from Yole, visit i-micronews in its LED Reports section.

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