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New Nanocrystals Show Potential for Cheap Lasers, New Lighting
May 11, 2009For more than a decade, scientists have been frustrated in their attempts to create continuously emitting light sources from individual molecules because of an optical quirk called "blinking," but now scientists at the University of Rochester have uncovered the basic physics behind the phenomenon, and along with researchers at the Eastman Kodak Company, created a nanocrystal that constantly emits light.
The findings, detailed online in today's issue of Nature, may open the door to dramatically less expensive and more versatile lasers, brighter LED lighting, and biological markers that track how a drug interact with a cell at a level never before possible.
Many molecules, as well as crystals just a billionth of a meter in size, can absorb or radiate photons. But they also experience random periods when they absorb a photon, but instead of the photon radiating away, its energy is transformed into heat. These "dark" periods alternate with periods when the molecule can radiate normally, leading to the appearance of them turning on and off, or blinking.
"A nanocrystal that has just absorbed the energy from a photon has two choices to rid itself of the excess energy-emission of light or of heat," says Todd Krauss, associate professor of chemistry at the University of Rochester and lead author on the study. "If the nanocrystal emits that energy as heat, you've essentially lost that energy."
Krauss worked with engineers at Kodak and researchers at the Naval Research Laboratory and Cornell University to discover the new, non-blinking nanocrystals.
Krauss, an expert in nanocrystals, and Keith Kahen, senior principal scientist of Kodak and an expert in optoelectronic materials and devices, were exploring new types of low-cost lighting similar to organic light-emitting diodes, but which might not suffer from the short lifespans and manufacturing challenges inherent in these diodes. Kahen, with help from Megan Hahn, a postdoctoral fellow in Krauss' laboratory, synthesized nanocrystals of various compositions.
Xiaoyong Wang, another postdoctoral fellow in Krauss laboratory, inspected one of these new nanocrystals and saw no evidence of the expected blinking phenomenon. Remarkably, even after four hours of monitoring, the new nanocrystal showed no sign of a single blink-unheard of when blinks usually happen on a scale of miliseconds to minutes.
After a lengthy investigation, Krauss and Alexander Efros from the Naval Research Laboratory concluded that the reason the blinking didn't occur was due to the unusual structure of the nanocrystal. Normally, nanocrystals have a core of one semiconductor material wrapped in a protective shell of another, with a sharp boundary dividing the two. The new nanocrystal, however, has a continuous gradient from a core of cadmium and selenium to a shell of zinc and selenium. That gradient squelches the processes that prevent photons from radiating, and the result is a stream of emitted photons as steady as the stream of absorbed photons.
With blink-free nanocrystals, Krauss believes lasers and lighting could be incredibly cheap and easy to fabricate. Currently, different color laser light is created using different materials and processes, but with the new nanocrystals a single fabrication process can create any color laser. To alter the light color, an engineer needs only to alter the size of the nanocrystal, which Krauss says is a relatively simple task.
The same is true of what could one day be OLED's successor, says Krauss. Essentially, "painting" a grid of differently sized nanocrystals onto a flat surface could create computer displays as thin as paper, or a wall that lights a room in any desired color.
This research was funded by the Eastman Kodak Company, the U.S. Department of Energy, the National Science Foundation, the University of Rochester Center for Electronic Imaging Systems, the Cornell Center for Nanoscale Systems, the Office of Naval Research, and the Alexander von Humboldt Foundation.
The University of Rochester
"A nanocrystal that has just absorbed the energy from a photon has two choices to rid itself of the excess energy-emission of light or of heat," says Todd Krauss, associate professor of chemistry at the University of Rochester and lead author on the study. "If the nanocrystal emits that energy as heat, you've essentially lost that energy."
Krauss worked with engineers at Kodak and researchers at the Naval Research Laboratory and Cornell University to discover the new, non-blinking nanocrystals.
Krauss, an expert in nanocrystals, and Keith Kahen, senior principal scientist of Kodak and an expert in optoelectronic materials and devices, were exploring new types of low-cost lighting similar to organic light-emitting diodes, but which might not suffer from the short lifespans and manufacturing challenges inherent in these diodes. Kahen, with help from Megan Hahn, a postdoctoral fellow in Krauss' laboratory, synthesized nanocrystals of various compositions.
Xiaoyong Wang, another postdoctoral fellow in Krauss laboratory, inspected one of these new nanocrystals and saw no evidence of the expected blinking phenomenon. Remarkably, even after four hours of monitoring, the new nanocrystal showed no sign of a single blink-unheard of when blinks usually happen on a scale of miliseconds to minutes.
After a lengthy investigation, Krauss and Alexander Efros from the Naval Research Laboratory concluded that the reason the blinking didn't occur was due to the unusual structure of the nanocrystal. Normally, nanocrystals have a core of one semiconductor material wrapped in a protective shell of another, with a sharp boundary dividing the two. The new nanocrystal, however, has a continuous gradient from a core of cadmium and selenium to a shell of zinc and selenium. That gradient squelches the processes that prevent photons from radiating, and the result is a stream of emitted photons as steady as the stream of absorbed photons.
With blink-free nanocrystals, Krauss believes lasers and lighting could be incredibly cheap and easy to fabricate. Currently, different color laser light is created using different materials and processes, but with the new nanocrystals a single fabrication process can create any color laser. To alter the light color, an engineer needs only to alter the size of the nanocrystal, which Krauss says is a relatively simple task.
The same is true of what could one day be OLED's successor, says Krauss. Essentially, "painting" a grid of differently sized nanocrystals onto a flat surface could create computer displays as thin as paper, or a wall that lights a room in any desired color.
This research was funded by the Eastman Kodak Company, the U.S. Department of Energy, the National Science Foundation, the University of Rochester Center for Electronic Imaging Systems, the Cornell Center for Nanoscale Systems, the Office of Naval Research, and the Alexander von Humboldt Foundation.
The University of Rochester
Nanocrystals Current Events and Nanocrystals News RSSTransforming Nanowires Into Nano-Tools Using Cation Exchange Reactions
A team of engineers from the University of Pennsylvania has transformed simple nanowires into reconfigurable materials and circuits, demonstrating a novel, self-assembling method for chemically creating nanoscale structures that are not possible to grow or obtain otherwise.
Gold Solution for Enhancing Nanocrystal Electrical Conductance
In a development that holds much promise for the future of solar cells made from nanocrystals, and the use of solar energy to produce clean and renewable liquid transportation fuels, researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have reported a technique by which the electrical conductivity of nanorod crystals of the semiconductor cadmium-selenide was increased 100,000 times.
Building better bone replacements with bacteria
Bacteria that manufacture hydroxyapatite (HA) could be used to make stronger, more durable bone implants. Professor Lynne Macaskie from the University of Birmingham this week (7-10 September) presented work to the Society for General Microbiology's meeting at Heriot-Watt University, Edinburgh.
Pitt researchers harness carbon nanomaterials for drug delivery systems, oxygen sensors
Two nanoscale devices recently reported by University of Pittsburgh researchers in two separate journals harness the potential of carbon nanomaterials to enhance technologies for drug or imaging agent delivery and energy storage systems, in one case, and, in the other, bolster the sensitivity of oxygen sensors essential in confined settings, from mines to spacecrafts.
Growth Spurts: Berkeley Lab Researchers Record First Real-Time Direct Observations of Nanocrystal Growth in Solution
The veil is being lifted from the once unseen world of molecular activity. Not so long ago only the final products were visible and scientists were forced to gauge the processes behind those products by ensemble averages of many molecules.
Jet-propelled Imaging for an Ultrafast Light Source
John Spence, a physicist at Arizona State University, is a longtime user of the Advanced Light Source at Lawrence Berkeley National Laboratory, where he has contributed to major advances in lensless imaging.
More Than Meets the Eye: New Blue Light Nanocrystals
Berkeley Lab researchers have produced non-toxic magnesium oxide nanocrystals that efficiently emit blue light and could also play a role in long-term storage of carbon dioxide, a potential means of tempering the effects of global warming.
Nanocrystals Reveal Activity Within Cells
Researchers at the U.S. Department of Energy's (DOE) Lawrence Berkeley National Laboratory have created bright, stable and bio-friendly nanocrystals that act as individual investigators of activity within a cell.
Major Breakthrough in Early Detection and Prevention of AMD
A team of researchers led by Dr. Jayakrishna Ambati at the University of Kentucky has discovered a biological marker for neovascular age-related macular degeneration (AMD), the leading cause of blindness in older adults.
Discovery of non-blinking semiconductor nanocrystals advances their applications
Substantial advances for applications of nanocrystals in the fields requiring a continuous output of photons and high quantum efficiency may soon be realized due to discovery of non-blinking semiconductor nanocrystals.
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