May 10, 2012
New Research Could Peg Quantum Dots As Future Of Lighting
Researchers are looking to white-light quantum dots as the future of lighting.
White-light quantum dots are ultra-small fluorescent beads of cadmium selenide that are able to convert blue light produced by an LED into a warm white light similar to an incandescent light.Vanderbilt University researchers are reporting that they have successfully boosted the fluorescent efficiency in nano crystals from an original level of three percent to as high as 45 percent. This feat proves that the lights efficiency is not too low for commercial applications.
“Forty-five percent is as high as the efficiency of some commercial phosphors which suggests that white-light quantum dots can now be used in some special lighting applications,” Sandra Rosenthal, who directed the research published in the Journal of the American Chemical Society, said in a press release.
“The fact that we have successfully boosted their efficiency by more than 10 times also means that it should be possible to improve their efficiency even further.”
The measurement of the overall efficiency of lighting devices is known as luminous efficiency. This measurement considers the amount of visible light a device produces per watt.
By comparison, an incandescent light bulb produces about 15 lumens per watt, while fluorescent tubes put out about 100 lumens per watt. LED lights currently range from 28 to 93 lumen per watt.
“We calculate that if you combine our enhanced quantum dots with the most efficient ultraviolet LED, the hybrid device would have a luminous efficiency of about 40 lumens/watt,” James McBride, research assistant professor of chemistry, said. “There is lots of room to improve the efficiency of UV LEDS and the improvements would translate directly into a higher efficiencies in the hybrid.”
Quantum dots, which were first discovered in 1980, are beads of semiconductor material that are so small, they have unique electronic properties.
One of the useful properties of quantum dots is fluorescence. They produce distinctive colors determined by the size of the particles.
As the size of the nanocrystal shrinks, the quantum dots light color shifts from red to blue, while the ultra-small quantum dots emit white instead.
“These quantum dots are so small that almost all of the atoms are on the surface, so the white-light emission is intrinsically a surface phenomena,” Rosenthal said.
In the latest study, the researchers set out to see if treating the quantum dots with metal salts would help them brighten up. They found that some of the salts produced a 10 to 20 percent improvement.
“They were acetate salts and they smelled a bit like acetic acid,” McBride said in a press release. “We knew that acetic acid binds to the quantum dots so we decided to give it a try.”
The team then found that acetic acid treatment helped bump up the quantum dots fluorescent efficiency from eight percent to 20 percent. The researchers also tried other members of this carbocyclic acid family, helping boost the efficiency to as high as 45 percent.
The researchers said their next step is to test different methods for encapsulating the enhanced quantum dots.