A method to tune the colour of the light emitted by an LED by altering the size of its semiconductor crystals has been discovered researchers from Ludwig-Maximilians-Universitaet (LMU) in Munich and the Johannes Kepler University (JKU) in Austria.
Light-emitting diodes (LEDs) produce light of a defined colour within the spectral range from the infrared to the ultraviolet. The exact wavelength of the emission is determined by the chemical composition of the semiconductor employed.
In the case of some semiconducting materials, the colour can also be tuned by appropriately modifying the size of the crystals of which the light-emitting layer is composed.
The researchers have developed a method for the production of semiconducting nanocrystals of a defined size based on the cheap mineral oxide known as perovskite. These crystals are said to be extremely stable – which ensures that the LEDs exhibit high colour fidelity – and the resulting semiconductors can be printed on surfaces.
Using a scalable and economical electrochemical process, a thin wafer was patterned like a waffle. The depressions served as tiny reaction vessels, whose shape and volume ultimately determined the size of the nanocrystals.
“Our nanostructure oxide layers also prevent contact between the semiconductor crystals and deleterious environmental factors such as free oxygen and water, which limit the working lifetime of the LEDs,” explains JKU Dr Martin Kaltenbrunner.