Nanotech lighting the way

Researchers at the University of Toronto have developed particles that potentially will make it easy, and cheap, to see in the dark.

The nanoparticles--developed under a project directed by professor Ted Sargent--can essentially detect infrared light, unseen by humans because of its long wavelengths. And like a solar panel, they can channel the energy to beneficial purposes.

Night vision binoculars and low-light cameras currently can produce images using the infrared spectrum, but the semiconductors inside these devices are complex to manufacture and expensive.

Conceivably, a manufacturer could mix the particles developed by Sargent into coatings, fabrics or plastics, and devise far less-expensive products. A specially treated camera lens could capture images in the dark by fielding infrared signals. Walls treated with infrared-sensitive paint could detect intruders or animals by intercepting their thermal signature, or body heat.

"You can see things not because of sunlight but because of temperature or heat," Sargent said. "Military technology is already there, but it is too expensive for you or me to put in the backyard."

The technology could appear in products in three to five years, Sargent added.

One unexpected benefit of the particles is that they can also capture infrared energy from the sun and turn it into electricity, which could boost the performance of flexible solar cells.

A number of companies, including Konarka Technologies, are trying to replace rigid and fairly unattractive crystalline solar panels with sheets of clear plastic that could be unobtrusively molded onto a roof or the side of a building.

Unfortunately, to date, polymer solar cells, which harvest energy from the visible spectrum, aren't very efficient. Current experimental polymers only convert between 3 percent and 12 percent of the sunlight that hits them into electricity.

By incorporating infrared particles, polymer solar cells could potentially harvest up to 30 percent of the total energy from the sun, according to Peter Peumans, a professor at Stanford University who has examined some of the experimental results in Toronto.

"Half of the energy reaching the earth from the sun is from the invisible spectrum," Sargent said. "What we've done is shown that with a plastic, you can access the infrared part of the sun spectrum."

The secret ingredient, both in terms of seeing in the dark and capturing the sun's energy, is carbon.

The infrared-sensitive nanocrystals created at the university consist of about eight carbon atoms strung together in a chain. Carbon is the element inside nanotubes--strong, electrically active particles that someday may be used in airplane wings and semiconductors.

The range of potential applications of these materials is broad. Some companies are currently experimenting with diamond and nanotube-based TV screens, while other researchers believe that carbon dots could deliver drugs to particular organs.

"The key was finding the right molecules to wrap around our nanoparticles," said Steve MacDonald, a University of Toronto grad student who helped develop a solar cell containing the infrared-sensitive particles. "Too long and the particles couldn't deliver their electrical energy to our circuit--too short and they clumped up, losing their nanoscale properties."

This work, in part, builds on earlier research conducted by Sargent, in which the professor and graduate students showed how nanotubes embedded in polymer could emit light.