A new optical scattering and absorbing material created by an international group, including scientists from Germany, Moldova, Denmark, and Australia, consists of microscopic tetrapods made of aerographite carbon, with these microtetrapods covered with a "fur" of much smaller nanotetrapods made of zinc oxide (ZnO) crystals. The material demonstrates photoabsorption in the UV and visible regions because of the wide bandgap of ZnO and its intrinsic defects, and photoabsorption in the infrared (IR) because of the architecture of the ZnO nanostructures and their doping by carbon impurities. The tetrapod mixture can be attached to stretchable substrates if desired.
In addition to defects in the ZnO crystalline structure, possible mechanisms for absorption of light in the visible and IR by ZnO include whispering-gallery modes (WGMs), second-harmonic generation (SHG), and others. Photoabsorption via WGMs is very dependent on the detailed physical shape of the crystals, whereas SHG-related absorption is also related to the size of the ZnO structures, the crystals' quality, surface defects, grain boundaries, and impurities. The scattering effect of the new aerographite/ZnO hybrid material could be used in laser-based lighting (such as headlights) in the automobile industry and elsewhere to diffuse the laser light just enough so that it is not hazardous to the human eye, while maintaining the laser light's high power. Reference: I. Tiginyanu et al., Sci. Rep., 6, 32913 (2016); doi:10.1038/srep32913.
