Tuning structural colors
New method could lead to displays based on structural colors.
Researchers at Linköping University have developed a method that may lead to new types of displays based on structural colors. The discovery opens the way to cheap and energy-efficient color displays and electronic labels. Structural colors can arise when light is internally reflected inside the material on a scale of nanometers. This is usually referred to as interference effects. An example found in nature are peacock feathers, which are fundamentally brown but acquire their characteristic blue-green sheen from small structural features.
The color of each light-emitting diode depends on the molecules from which it is built, or in other words, its pigment. However, it is relatively expensive to manufacture light-emitting diodes, and the global use of emissive displays consumes a lot of energy. Another type of display, reflective displays, is therefore being explored for purposes such as tablet computers used as e-readers, and electronic labels. Reflective displays form images by controlling how incident light from the surroundings is reflected, which means that they do not need their own source of illumination. However, most reflective displays are intrinsically monochrome, and attempts to create color versions have been rather complicated and have sometimes given poor results.
Shangzhi Chen at the Laboratory of Organic Electronics at Linköping University describes a new type of dynamic structural color image. “We have developed a simple method to produce structural colour images with electrically conducting plastics, or conducting polymers. The polymer is applied at nanoscale thicknesses onto a mirror by a technique known as vapour phase polymerisation, after the substrate has been illuminated with UV light. The stronger the UV illumination, the thicker the polymer film, and this allows us to control the structural colors that appear at different locations on the substrate.”
The method can produce all colors in the visible spectrum. Furthermore, the colors can be subsequently adjusted using electrochemical variation of the redox state of the polymer. This function has been popular for monochrome reflective displays, and the new study shows that the same materials can provide dynamic images in color using optical interference effects combined with spatial control of nanoscale thicknesses. Magnus Jonsson, associate professor at the Laboratory of Organic Electronics at Linköping University, believes that the method has great potential, for example, for applications such as electronic labels in colour. Further research may also allow more advanced displays to be manufactured.
“We receive increasing amounts of information via digital displays, and if we can contribute to more people gaining access to information through cheap and energy-efficient displays, that would be a major benefit. But much research remains to be done, and new projects are already under way”, says Magnus Jonsson. (Source: LIU)
