Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


'Flying saucer' quantum dots hold secret to brighter, better lasers


Research team led by U of T Engineering 'squashes' the shape of nanoparticles, enabling inexpensive lasers that continuously emit light in a customized rainbow of colors

Fresh insights into living cells, brighter video projectors and more accurate medical tests are just three of the innovations that could result from a new way of fabricating lasers.

This computer-generated model shows the spherical core of the quantum dot nanoparticle (in red) along with the 'flying saucer' shape of the outer shell (in yellow). The tension in the core induced by the shell affects the electronic states and lowers the energy threshold required to trigger the laser.

Credit: Dr. Alex Voznyy/U of T Engineering

The new method, developed by an international research team from U of T Engineering, Vanderbilt University, the Los Alamos National Laboratory and others, produces continuous laser light that is brighter, less expensive and more tuneable than current devices by using nanoparticles known as quantum dots.

"We've been working with quantum dots for more than a decade," says Ted Sargent, a professor in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at U of T. "They are more than five thousand times smaller than the width of a human hair, which enables them to straddle the worlds of quantum and classical physics and gives them useful optical properties."

"Quantum dots are well-known bright light emitters," says Alex Voznyy, a senior research associate in Sargent's lab. "They can absorb a lot of energy and re-emit it at a particular frequency, which makes them a particularly suitable material for lasers."

By carefully controlling the size of the quantum dots, the researchers in Sargent's lab can 'tune' the frequency, or colour, of the emitted light to any desired value. By contrast, most commercial lasers are limited to one specific frequency, or a very small range, defined by the materials they are made from.

The ability to produce a laser of any desired frequency from a single material would give a boost to scientists looking to study diseases at the level of tissues or individual cells by offering new tools to probe biochemical reactions. They could also enable laser display projectors that would be brighter and more energy efficient than current LCD technology.

But although the ability of colloidal quantum dots to produce laser light was first demonstrated by co-author Victor Klimov and his team at Los Alamos National Laboratory more than 15 years ago, commercial application has remained elusive. A key problem has been that until now, the amount of light needed to excite the quantum dots to produce laser light has been very high.

"You have to stimulate the laser using more and more power, but there are a lot of heating losses as well," says Voznyy. "Eventually it gets so hot that it just burns." Most quantum dot lasers are limited to pulses of light lasting just a few nanoseconds -- billionths of a second.

The team, which included Voznyy, postdoctoral researchers Fengjia Fan and Randy Sabatini and MASc candidate Kris Bicanic, overcame this problem by changing the shape of the quantum dots, rather than their size. They were able to create quantum dots with a spherical core and a shell shaped like a Skittle, an M&M or a flying saucer -- a 'squashed' spherical shape known as an oblate spheroid.

The mismatch between the shape of the core and the shell introduces a tension that affects the electronic states of the quantum dot, lowering the amount of energy needed to trigger the laser. As reported in a paper published today in Nature, the innovation means that the quantum dots are no longer in danger of overheating, so the resulting laser can fire continuously.

While quantum dots are often built by depositing molecules one at a time in a vacuum, Sargent's team mixes together liquid solutions that contain various quantum dot precursors. When the solutions react, they produce solid quantum dots that stay suspended in the liquid -- these are known as colloidal quantum dots. The team's key innovation was to add specific capping molecules into the mix, which allowed them to control the shape of the particles to obtain the desired properties, an approach Fan calls 'smart chemistry'.

"Solution-based processing greatly reduces the cost of making quantum dots," says Fan. "It will also make it easier to scale up production, because we can use techniques already established in the printing industry."

The project included a number of national and international partners. Computer simulations in collaboration with the University of Ottawa and the National Research Council guided the design of the quantum dots. Analytical tests from Vanderbilt's Institute of Nanoscale Science and Engineering in Nashville, TN, as well as the University of New Mexico's Center for High Technology Materials in Albuquerque, NM and Los Alamos confirmed that the final products had the desired shape, composition and behaviour by analyzing individual quantum dots at the atomic level.

"We were impressed not only by the engineered structure itself but also by the level of uniformity they have achieved," says Sandra Rosenthal, director of the Vanderbilt Institute for Nanoscale Science and Engineering. "Sargent's team has managed to create quantum dots with a unique and elegant structure. This is exciting research."

The team has more work to do before they can look to commercialization. "For this proof-of-concept device, we're exciting the quantum dots with light," says Sabatini. "Ultimately, we want to move to exciting them with electricity. We also want to scale up the power to milliwatts or even watts. If we can do that, then it becomes important for laser projection."

Marit Mitchell | EurekAlert!

More articles from Physics and Astronomy:

nachricht Space observation with radar to secure Germany's space infrastructure
23.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR

nachricht Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1
21.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Space observation with radar to secure Germany's space infrastructure

Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.

The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

New solar solutions for sustainable buildings and cities

23.03.2018 | Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

Latest News

Don't Give the Slightest Chance to Toxic Elements in Medicinal Products

23.03.2018 | Life Sciences

Sensitive grip

23.03.2018 | Materials Sciences

No compromises: Combining the benefits of 3D printing and casting

23.03.2018 | Process Engineering

Science & Research
Overview of more VideoLinks >>>