Photonics traps the rainbow

Iridescence is an optical phenomenon that produces the reflection of different colours and can often be observed in nature. Some examples of iridescence are the multicoloured feathers of peacock, some scales of reef fish, the bluish-green colours of beetles and some butterflies, and even some fruits or berries. In these cases, the colours that appear are not due to pigmentation, but to the optical phenomenon of iridescence, which is caused by the multiple reflections of light on delicate semi-transparent surfaces that are separated by distances similar to the wavelength of the light passing through them. It is precisely this generation of artificial iridescence that is one of the objectives of the IMM-CSIC Nanophotonic Devices Group. The group has recently developed a technology that allows the generation of iridescent surfaces on practically any material, including organic and biocompatible materials, such as natural silk. Figure 2 shows some unretouched photographs of surfaces of this type, which show diverse and highly intense iridescences that change their colour depending on the direction in which they are viewed. Moreover, these surfaces have hydrophobic or hydrophilic properties and also antibacterial, selectable depending on the type of nanostructure used. To produce them, CSIC has developed a technology -in the process of patent- that is very simple and low cost, besides being able to be used on practically any type of material, including human skin or nails. The applications of these iridescent surfaces are multiple and range from chromatic marking without the use of inks to the development of cosmetic products based on biocompatible materials, such as silks or natural lacquers.