Exploiting new 'strain engineering' approach produces highly stable, narrow linewidth light from individual quantum dots
Intentionally "squashing" colloidal quantum dots during chemical synthesis creates dots capable of stable, "blink-free" light emission that is fully comparable with the light produced by dots made with more complex processes. The squashed dots emit spectrally narrow light with a highly stable intensity and a non-fluctuating emission energy.
Novel colloidal quantum dots are formed of an emitting cadmium/selenium (Cd/Se) core enclosed into a compositionally graded CdxZn1-xSe shell wherein the fraction of zinc versus cadmium increases towards the dot's periphery. Due to a directionally asymmetric lattice mismatch between CdSe and ZnSe, the core, at top right, is compressed more strongly perpendicular to the crystal axis than along it. This leads to modifications of the electronic structure of the CdSe core, which beneficially affects its light-emission properties. Bottom image: Experimental traces of emission intensity from a conventional quantum dot (upper panel) and a novel asymmetrically compressed quantum dot (lower panel) resolved spectrally and temporally. The emission from the conventional quantum dot shows strong spectral fluctuations ("spectral jumps" and "spectral diffusion"). The emission from the asymmetrically compressed quantum dots is highly stable in both intensity and spectral domains. In addition, it shows a much narrower linewidth, which is below the room-temperature thermal energy (25 meV).
Credit: Los Alamos National Laboratory
New research at Los Alamos National Laboratory suggests that the strained colloidal quantum dots represent a viable alternative to presently employed nanoscale light sources, and they deserve exploration as single-particle, nanoscale light sources for optical "quantum" circuits, ultrasensitive sensors, and medical diagnostics.
"In addition to exhibiting greatly improved performance over traditional produced quantum dots, these new strained dots could offer unprecedented flexibility in manipulating their emission color, in combination with the unusually narrow, 'subthermal' linewidth," said Victor Klimov, lead Los Alamos researcher on the project.
"The squashed dots also show compatibility with virtually any substrate or embedding medium as well as various chemical and biological environments."
The new colloidal processing techniques allow for preparation of virtually ideal quantum-dot emitters with nearly 100 percent emission quantum yields shown for a wide range of visible, infrared and ultraviolet wavelengths. These advances have been exploited in a variety of light-emission technologies, resulting in successful commercialization of quantum-dot displays and TV sets.
The next frontier is exploration of colloidal quantum dots as single-particle, nanoscale light sources. Such future "single-dot" technologies would require particles with highly stable, nonfluctuating spectral characteristics.
Recently, there has been considerable progress in eliminating random variations in emission intensity by protecting a small emitting core with an especially thick outer layer. However, these thick-shell structures still exhibit strong fluctuations in emission spectra.
In a new publication in the journal Nature Materials, Los Alamos researchers demonstrated that spectral fluctuations in single-dot emission can be nearly completely suppressed by applying a new method of "strain engineering." The key in this approach is to combine in a core/shell motif two semiconductors with directionally asymmetric lattice mismatch, which results in anisotropic compression of the emitting core.
This modifies the structures of electronic states of a quantum dot and thereby its light emitting properties. One implication of these changes is the realization of the regime of local charge neutrality of the emitting "exciton" state, which greatly reduces its coupling to lattice vibrations and fluctuating electrostatic environment, key to suppressing fluctuations in the emitted spectrum.
An additional benefit of the modified electronic structures is dramatic narrowing of the emission linewidth, which becomes smaller than the room-temperature thermal energy.
Publication: Young-Shin Park, Jaehoon Lim, and Victor I. Klimov, Asymmetrically Strained Quantum Dots with Nonfluctuating Single-Dot Emission Spectra and Subthermal Room-Temperature Linewidths, Nature Materials, January 7, 2019. DOI: 10.1038/s41563-018-0254-7
Project members: Young-Shin Park (Research Scientist, LANL & UNM), Jaehoon Lim (Postdoctoral Research Associate), Victor I. Klimov (Laboratory Fellow, Project Leader).
Funding: Single-dot spectroscopic studies were funded by the U.S. Department of Energy's Office of Science. The work on quantum dot synthesis was supported by the Laboratory Directed Research and Development program at Los Alamos National Laboratory.
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 Triad, a public service oriented, national security science organization equally owned by its three founding members: Battelle Memorial Institute (Battelle), the Texas A&M University System (TAMUS), and the Regents of the University of California (UC) 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.
Nancy Ambrosiano | EurekAlert!
The taming of the light screw
22.03.2019 | Max-Planck-Institut für Struktur und Dynamik der Materie
21.03.2019 | Max-Planck-Institut für Polymerforschung
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
22.03.2019 | Life Sciences
22.03.2019 | Life Sciences
22.03.2019 | Information Technology