Electricity lights up nanocrystals

02 May 2003

Scientists see electroluminescence at communications wavelengths from lead sulphide nanocrystals.

Researchers in Canada have seen tunable electroluminescence from lead sulphide (PbS) nanocrystals for the first time. By varying the diameter of the nanocrystals, the team from the University of Toronto generated light in the range 1000 to 1600 nm. As this covers important communications wavelengths at 1300 and 1550 nm, the team says its tiny 5-nm diameter crystals could find uses in devices such as light modulators, waveguides and optical chips. (Applied Physics Letters 82 2895)

"Our study is the first to demonstrate experimentally that we can convert electrical current into light using this particularly promising class of nanocrystals," said Ted Sargent from the University of Toronto's Electrical and Computer Engineering Department.

In the past, nanocrystals that emit light at communications wavelengths have been fabricated in a vacuum at temperatures approaching 600 to 800°C. Here, Sargent teamed up with Gregory Scholes and colleagues from the university's chemistry department to develop a more cost-effective and practical approach.

The new technique allowed Sargent and colleagues to work at atmospheric pressure and temperatures less than 150°C, but the resulting nanocrystals had unstable surfaces. To stabilize the crystals, the team coated them with oleate ligands before embedding them in a semiconductor polymer matrix.

The end result was a thin-film of so-called "hybrid" polymer, which is electroluminescent. The team reports that the electroluminscence signal increased dramatically near a bias voltage of 3 V and corresponded to an internal quantum efficiency of up to 1.2%.

"Our work represents a step towards the integration of many fiber-optic communications devices one chip," said Sargent. "We've shown that our hybrid plastic can convert electric current into light, with promising efficiency and with a defined path towards further improvement."

Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.