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Nanowires Influence Direction, Intensity of LEDs
Jul 2011
AMSTERDAM, Netherlands, July 5, 2011 — A new method for controlling the direction and intensity of LED light emission consists of growing partially emitting nanowires that form an ordered pattern, creating a "photonic crystal" that sends light in specific directions.

Electron microscope image of nanowires. (Images: FOM Institute AMOLF)

Researchers from the Foundation for Fundamental Research on Matter (FOM) Institute AMOLF, together with colleagues from Philips Research, Eindhoven University of Technology and Delft University of Technology, made the special nanostructures that they say could be a key step toward a new generation of LEDs based on semiconducting nanowires.

The direction in which an LED emits light is determined mainly by the surface between the LED and the surrounding air. As light can escape from the LED only at small angles, the direction of emission is usually straight on (perpendicular to the surface). However, the direction can be influenced by nanostructures on the surface of the LED, which inspired the new technology.

Measurement of the intensity of the light emitted by the nanowires is a function of the wavelength (i.e., color) and of the angle of the light emitted. The maximum depends on the emitter, which is located in the nanowires. In this case, it is at 950 nm and 55 degrees.

The photonic crystal formed of partially emitting nanowires sends light in specific directions. The researchers showed that the emission can be optimized by a smart positioning of the emitting part within the nanowire. They said that this knowledge could lead to more energy-efficient LEDs and could provide opportunities for a next generation of semiconducting nanowire-based LEDs.

This research is an outgrowth of the Industrial Partnership Programme "Improved solid-state light sources," sponsored by FOM and Philips, and of the FOM Programme "NanoPhotovoltaics." It also received support from Technology Foundation STW.

The results of the study were published in the journal ACS Nano.

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