news digest ♦ Novel Devices
group at Brown. Because of their improved quantum mechanical and electrical performance, he said, the coated pyramids require 10 times less pulsed energy or 1,000 times less power to produce laser light than previous attempts at the technology.
Quantum nail polish
When chemists at QDVision brew a batch of colloidal quantum dots for Brown-designed specifications, Dang and Nurmikko get a vial of a viscous liquid that Nurmikko said somewhat resembles nail polish.
To make a laser, Dang coats a square of glass, or a variety of other shapes, with the liquid. When the liquid evaporates, what’s left on the glass are several densely packed solid, highly ordered layers of the nanocrystals. By sandwiching that glass between two specially prepared mirrors, Dang creates one of a VCSEL. The Brown-led team says it was the first to make a working VCSEL with colloidal quantum dots.
The nanocrystals’ outer coating alloy of zinc, cadmium, sulphur and that molecular glue is important because it reduces an excited electronic state requirement for lasing and protects the nanocrystals from a kind of crosstalk that makes it hard to produce laser light, Nurmikko says. Every batch of colloidal quantum dots has a few defective ones, but normally just a few are enough to interfere with light amplification.
Faced with a high excited electronic state requirement and destructive crosstalk in a densely packed layer, previous groups have needed to pump their dots with a lot of power to push them past a higher threshold for producing light amplification, a core element of any laser.
Pumping them intensely, however, gives rise to another problem: an excess of excited electronic states called excitons. When there are too many of these excitons among the quantum dots, energy that could be producing light is instead more likely to be lost as heat, mostly through a phenomenon known as the Auger process.
The nanocrystals’ structure and outer cladding reduces destructive crosstalk and lowers the energy needed to get the quantum dots to shine. That reduces the energy required to pump the quantum
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dot laser and significantly reduces the likelihood of exceeding the level of excitons at which the Auger process drains energy away. In addition, a benefit of the new approach’s structure is that the dots can act more quickly, releasing light before Auger process can get started, even in the rare cases when it still does start.
“We have managed to show that it’s possible to create not only light, but laser light,” Nurmikko says. “In principle, we now have some benefits: using the same chemistry for all colours, producing lasers in a very inexpensive way, relatively speaking, and the ability to apply them to all kinds of surfaces regardless of shape. That makes possible all kinds of device configurations for the future.”
The US. Department of Energy, the Air Force Office for Scientific Research, and the National Science Foundation supported the research. Dang is a Vietnam Education Foundation (VEF) Scholar.
Further details of this work has been published in the paper,”Red, green and blue lasing enabled by single-exciton gain in colloidal quantum dot films”, by Dang et al, Nature Nanotechnology, 7, 335–339 (2012). DOI:10.1038/nnano.2012.61
Global QD market to shoot up to $7480.25 million by 2022
Apart from in healthcare, where Quantum Dots hold a large market share, the technology is expected to play a major part in LED lighting and solar cells in the future
A new report, “Quantum Dots (QD) Market - Global Forecast & Analysis (2012 - 2022)” published by MarketsandMarkets, says the total market for Quantum dots is expected to reach over $7480 million by 2022, at a CAGR of 55.2% from 2012 to 2022.
Quantum Dots (QD) are one of the most advanced area of “semiconductor nanoparticles”, and is currently undergoing massive research.
QDs are semiconductor nanoparticles, and, as the name suggests, have size from 2 nm to 10 nm. Due
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