‘Quantum dot’ technology may help light the future


'Quantum dot' technology may help light the future
The orange color in the letters ‘OSU’ is produced from ‘quantum dots’ viewed under a microscope, as they absorb blue light and emit the light as orange — an illustration of some of the potential of new technology being developed at Oregon State University. Credit: Oregon State University

Advances at Oregon State University in manufacturing technology for “quantum dots” may soon lead to a new generation of LED lighting that produces a more user-friendly white light, while using less toxic materials and low-cost manufacturing processes that take advantage of simple microwave heating.

The cost, environmental, and performance improvements could finally produce solid state lighting systems that consumers really like and help the nation cut its lighting bill almost in half, researchers say, compared to the cost of incandescent and .

The same technology may also be widely incorporated into improved lighting displays, computer screens, smart phones, televisions and other systems.

A key to the advances, which have been published in the Journal of Nanoparticle Research, is use of both a “continuous flow” chemical reactor, and technology that’s conceptually similar to the ovens that are part of almost every modern kitchen.

The continuous flow system is fast, cheap, energy efficient and will cut manufacturing costs. And the microwave heating technology will address a problem that so far has held back wider use of these systems, which is precise control of heat needed during the process. The microwave approach will translate into development of nanoparticles that are exactly the right size, shape and composition.

“There are a variety of products and technologies that can be applied to, but for mass consumer use, possibly the most important is improved LED lighting,” said Greg Herman, an associate professor and chemical engineer in the OSU College of Engineering.

“We may finally be able to produce low cost, energy efficient LED lighting with the soft quality of white light that people really want,” Herman said. “At the same time, this technology will use nontoxic materials and dramatically reduce the waste of the materials that are used, which translates to lower cost and environmental protection.”

Some of the best existing LED lighting now being produced at industrial levels, Herman said, uses cadmium, which is highly toxic. The system currently being tested and developed at OSU is based on , a much more benign material with high energy conversion efficiency.

Quantum dots are nanoparticles that can be used to emit light, and by precisely controlling the size of the particle, the color of the light can be controlled. They’ve been used for some time but can be expensive and lack optimal color control. The manufacturing techniques being developed at OSU, which should be able to scale up to large volumes for low-cost commercial applications, will provide new ways to offer the precision needed for better color control.

By comparison, some past systems to create these nanoparticles for uses in optics, electronics or even biomedicine have been slow, expensive, sometimes toxic and often wasteful.

Oher applications of these systems are also possible. Cell phones and might use less power and last much longer on a charge. “Taggants,” or compounds with specific infrared or visible light emissions, could be used for precise and instant identification, including control of counterfeit bills or products.

Quantum Dot Technology Could Lead To Solar Panel Windows.


Researchers from Los Alamos National Laboratory and the University of Milano-Bicocca have designed and synthesized a new generation of quantum dots for use in solar energy systems that overcome previous inefficiencies in harvesting sunlight. The study has been published in the journal Nature Photonics.

Quantum dots, which are nanocrystals made of semiconducting materials, appeal to scientists for use in solar photovoltaics (solar panel systems) because of their versatility and low-cost. In particular, they are desirable for use in luminescent solar concentrators (LSCs), which are photon-management devices that serve as alternatives to optics-based solar concentration systems.

LSCs are constructed from transparent materials containing emitters such as quantum dots. They concentrate solar radiation absorbed from a large area onto a significantly smaller solar cell, explains Victor Kilmov, one of the authors of the study. One exciting application of LSCs is the potential to develop photovoltaic windows, which could turn buildings into energy making factories.

Although quantum dots are highly efficient emitters, their small Stokes shift (the presence of an overlap between emission and absorption) means that some of the light produced is re-absorbed by the dots, resulting in losses of emission and therefore overall efficiency problems.

To resolve this issue, the team generated “Stokes-shift-engineered” giant quantum dots composed of a cadmium selenide (CdSe) shell which absorbs light, and a cadmium sulfide (CdS) core which is responsible for light emission. This separation of absorption and emission caused a significant reduction in re-absorption losses which previously caused inefficiencies. The dots were then incorporated into a high-quality polymethylmethacrylate (PMMA) matrix, and spectroscopic analysis revealed that re-absorption losses were minimal across distances of tens of centimeters.

The incorporation of the quantum dots into this PMMA matrix is not specific to a particular type of quantum dot; this means that it can be applied to different sized nanocrystals composed of various materials. This technology therefore represents a promising materials platform.