Nav: Home

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

March 20, 2017

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.

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."

University of Toronto Faculty of Applied Science & Engineering

Related Quantum Dots Articles:

What a pair! Coupled quantum dots may offer a new way to store quantum information
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have for the first time created and imaged a novel pair of quantum dots -- tiny islands of confined electric charge that act like interacting artificial atoms.
Spinning quantum dots
A new paper in EPJ B presents a theoretical analysis of electron spins in moving semiconductor quantum dots, showing how these can be controlled by electric fields in a way that suggests they may be usable as information storage and processing components of quantum computers.
Towards high quality ZnO quantum dots prospective for biomedical applications
Scientists from Warsaw together with colleagues from Grenoble have moved a step closer to creating stable, high quality colloidal zinc oxide quantum dots (ZnO QDs) for use in modern technologies and nanomedicine.
Controlling the charge state of organic molecule quantum dots in a 2D nanoarray
Australian researchers have fabricated a self-assembled, carbon-based nanofilm where the charge state (ie, electronically neutral or positive) can be controlled at the level of individual molecules.
Modified quantum dots capture more energy from light and lose less to heat
Los Alamos National Laboratory scientists have synthesized magnetically-doped quantum dots that capture the kinetic energy of electrons created by ultraviolet light before it's wasted as heat.
Using quantum dots and a smartphone to find killer bacteria
A combination of off-the-shelf quantum dot nanotechnology and a smartphone camera soon could allow doctors to identify antibiotic-resistant bacteria in just 40 minutes, potentially saving patient lives.
Synthesizing single-crystalline hexagonal graphene quantum dots
A KAIST team has designed a novel strategy for synthesizing single-crystalline graphene quantum dots, which emit stable blue light.
US Naval Research Laboratory 'connects the dots' for quantum networks
Researchers at the US Naval Research Laboratory developed a novel technique that could enable new technologies that use properties of quantum physics for computing, communication and sensing, which may lead to 'neuromorphic' or brain-inspired computing.
Quantum rebar: Quantum dots enhance stability of solar-harvesting perovskite crystals
Engineering researchers have combined two emerging technologies for next-generation solar power -- and discovered that each one helps stabilize the other.
2D gold quantum dots are atomically tunable with nanotubes
Gold atoms ski along boron nitride nanotubes and stabilize in metallic monolayers.
More Quantum Dots News and Quantum Dots Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at