February 4, 2013
New Quantum Dots Emit Constant Light At Near 100 Percent Efficiency
Michael Harper for redOrbit.com — Your Universe Online
In the 1980s, scientists discovered very tiny particles that are capable of emitting light when exposed to ultraviolet light. These particles — now known as quantum dots — are made of a semiconductor material and can display light in a wide array of colors depending on the size of the particle. Though these dots initially showed great promise for a number of purposes, several limitations have prevented them from being widely deployed in the field. Now, a team of MIT researchers has advanced the study of these quantum dots and showed how to overcome some of these barriers and even produce a better, more efficient quantum dot.
According to an MIT press release, their researchers have been able to overcome several obstacles with one study which will hopefully make it possible to begin using these light-emitting dots in multiple applications. This new research was published this week in the journal Nature Materials by postdoctoral student Ou Chen and Moungi Bawendi, the Lester Wolfe professor of chemistry at MIT.
The researchers worked on a specific type of quantum dots known as colloidal quantum dots which are made of tiny particles of semiconductor material so small that their properties differ from those of the bulk material. The unusual properties of colloidal quantum dots can be attributed in part to the fact that they are governed by the laws of quantum mechanics which describe how subatomic particles behave and are distinct from the laws of standard Newtonian physics. Of particular interest is the ability of these dots to emit bright fluorescent light in a wide array of colors after they have been illuminated with ultraviolet light.
Using new processing techniques, the MIT team has been able to shape dots with brighter emissions, near 100 percent energy efficiency, narrow peaks of emission, and uniform size and shape. According to MIT, narrower emission peaks mean more fine-grained control over which colors are produced by these dots.
One of the main limiting factors in quantum dot applications was their tendency to blink uncontrollably. Without a steady beam of light — especially when used in “marker” applications — these dots become more frustrating than helpful. This new research has almost eliminated this blinking entirely, creating a quantum dot that consistently remains lit and for a longer period of time.
Researchers have often thought that these dots could be of great service in the medical field, replacing the need for fluorescent dyes used in a number of diagnostic tests and research studies. These dots could also act as biomarkers, attaching themselves to cells and identifying by color which cells they have attached to. Their ability to attach to individual cells gives them an advantage over dyes, which generally do not offer such precision control.
When they blink, however, it can be difficult to determine which cells are marked with which dots, especially when these cells are being observed or photographed. By finding a way to keep these dots from blinking so frequently, the MIT researchers have potentially given doctors and scientists a better tool to observe these cells.
According to Chen, previous attempts have been made to reduce this blinking, but this usually involved placing thicker “shells” around the dots which made them larger and thus a poor candidate for quantum applications.
“[Our] dots are roughly the size of a protein molecule,” explains Chen. This miniscule size is helpful when biologists need to mark a cell but do not want the cell to be overwhelmed by the marker.
The team also speculates that these dots may even be used in television displays, offering precisely controlled color in a manner that is highly energy efficient.
Professor Bawendi is optimistic about his team´s ability to produce this new variety of quantum dots, saying that this new process is the first time a team has been able to “combine all these attributes that people think are important, at the same time.”
And the key to creating such an efficient and precise dot, says Bawendi, is taking it nice and slow during dot creation.
“A very important thing is synthesis speed,” he explains, “to give enough time to allow every atom to go to the right place.”
Chen has said that this speed should also make it relatively easy to scale up production to larger scales, hopefully leading to the first useful applications of these dots within the next two years.