Nav: Home

'Flying saucer' colloidal quantum dots produce brighter, better lasers

March 20, 2017

LOS ALAMOS, N.M., March 20, 2017-- A multi-institutional team of researchers from Canada and the US has demonstrated steady state lasing with solution-processed nanoparticles called "colloidal quantum dots," an important step on the path to improving laser tools for fiber optics, video projectors and more accurate medical testing technology. The work is reported today in a paper for the journal Nature.

"This work brings us a step closer to the next important goal - the demonstration of lasing with electrical pumping, at which point colloidal quantum dot laser diodes will become a technological reality," said Victor Klimov, a Los Alamos National Laboratory participant in the present project and principal contributor to the original demonstration of the quantum dot lasing effect. The new studies prove the feasibility of steady state lasing with colloidal quantum dots and provide practical guidelines to make them even better as optical-gain media. Improving quantum dot lasing could produce better tools for detailed, cellular-level biochemical analysis, and take video projectors to a more efficient level than the current LCD versions.

"They [quantum dots] 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," said project lead Ted Sargent, a professor in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto (U of T).

While quantum dots are often built by depositing molecules one at a time in a vacuum, the University of Toronto team mixed together liquid solutions that contain various quantum dot precursors. When the solutions react, they produce solid quantum dots that stay suspended in the liquid --colloidal quantum dots. "Solution-based processing greatly reduces the cost of making quantum dots," says Fengjia Fan, a U of T postdoctoral fellow and coauthor. "It will also make it easier to scale up production, because we can use techniques already established in the printing industry."

The research team includes the University of Toronto as a lead institution, Los Alamos National Laboratory, Vanderbilt University, University of New Mexico, National Research Council of Canada, and the University of Ottawa. For Los Alamos, the research connects to the institutional mission of solving national security challenges through scientific excellence, in this case focusing on novel physical principles for highly efficient light sources, charge manipulation in exploratory device structures, and novel nanomaterials.

Semiconductor quantum dots are tiny specs of matter whose emission color can be modified at will by simply varying particle size. This unique property has been already explored in commercial display technologies where quantum dots have expanded the palette of available colors.

But the challenge is that most quantum dot lasers are limited to pulses of light lasting just a few nanoseconds -- billionths of a second. The Toronto team 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 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 spreads apart the electronic states of the quantum dot, lowering the amount of energy needed to trigger the laser. As reported in today's paper, the innovation means that the quantum dots are no longer in danger of overheating, so the resulting laser can fire continuously.

The achievement of the lasing regime is also facilitated by unusually narrow emission linewidths of these quantum dots, revealed by single-dot spectroscopic measurements conducted at Los Alamos. This property increases the relative fraction of the dots participating in light amplification and helps further reduce the lasing threshold.

Quantum dots have long been envisioned as highly flexible optical gain media for solution-processible lasers, able to easily access any desired optical wavelength across the entire range. "The dream of such lasers has motivated much of the research at the early times of quantum dot era in the '80s and the '90s, until it culminated in the first practical demonstration of the lasing effect by the LANL quantum dot group in 2000," said Klimov. This groundbreaking discovery has stimulated a flurry of follow up work, uncovering novel and exciting photophysics. So far, however, it still has not produced a practical commercialized technology.

The main difficulty in making quantum dot lasers practical is extremely fast optical gain decay due to a feature called nonradiative Auger recombination. While techniques such as femtosecond pump lasers to outpace Auger recombination do work in the lab setting, they are too complex and expensive for real-life applications. Therefore, the Toronto team's demonstration of quantum dot lasing using steady-state but not pulsed excitation has been an important step on the way towards a practical lasing technology.
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 National Laboratory's Nanotechnology and Advanced Spectroscopy Team confirmed that the final products had the desired shape, composition and behavior by analyzing individual quantum dots at the atomic level.

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," said Randy Sabatini of U of T. "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."

Funding: The research of the Los Alamos team was supported by the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Paper: Continuous-wave lasing in colloidal quantum dot solids enabled by facet-selective epitaxy

Authors and affiliations:

Fengjia Fan1†, Oleksandr Voznyy1†, Randy P. Sabatini1†, Kristopher T. Bicanic1†, Michael M. Adachi1, James R. McBride2, Kemar R. Reid2, Young-Shin Park3,4, Xiyan Li1, Ankit Jain1, Rafael Quintero-Bermudez1, Mayuran Saravanapavanantham1, Min Liu1, Marek Korkusinski5, Pawel Hawrylak6, Victor I. Klimov3, Sandra J. Rosenthal2, Sjoerd Hoogland1, Edward H. Sargent1

1. Department of Electrical and Computer Engineering, University of Toronto, Canada

2. The Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, USA

3. Chemistry Division, Los Alamos National Laboratory, New Mexico, USA

4. Center for High Technology Materials, University of New Mexico, USA

5. Security and Disruptive Technologies Emerging Technologies Division, National Research Council, Ottawa, Canada

About Los Alamos National Laboratory

Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, BWX Technologies, Inc. and URS Corporation for the Department of Energy's National Nuclear Security Administration.

Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health and global security concerns.

DOE/Los Alamos National Laboratory

Related Quantum Dots Articles:

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.
Graphene quantum dots for single electron transistors
Scientists from the Higher School of Economics, Manchester University, the Ulsan National Institute of Science & Technology and the Korea Institute of Science and Technology have developed a novel technology, which combines the fabrication procedures of planar and vertical heterostructures in order to assemble graphene-based single-electron transistors of excellent quality.
Quantum dots can spit out clone-like photons
MIT and ETH Zurich researchers have produced coherent single photon emitters, a key component for future quantum computers and communications systems.
More Quantum Dots News and Quantum Dots Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab