Feathered photonic crystal takes off

28 Oct 2008

Natural photonic crystals found within peacock feathers are being used to tune the optical emission of embedded ZnO nanoparticles.

Peacock feather

Peacock feathers are a particularly striking example of Mother Nature's work in the field of photonic crystals, but do they have what it takes to become building blocks in future optoelectronic devices? Tiny optical cavities within the bird's feathers give the peacock its colourful appearance by converting light into a palette of blues, greens, reds and yellows, and it's this ability that Huilan Su and his colleagues are keen to exploit.

"Natural photonic crystals are superior choices when you consider the high cost and limited patterns of artificial structures," Su, a researcher at Shanghai Jiaotong University's State Key Lab of Metal Matrix Composites, told nanotechweb.org. "By embedding zinc oxide (ZnO) nanoparticles inside a section of peacock feather, we hope to create an affordable device for tuning photoluminescent emission."

When nanoscale ZnO is excited by ultraviolet radiation (360 nm) the material typically displays two emission bands – a violet emission around 420 nm and a green luminescence centred at 550 nm. The output is a good match for the peacock feather, which has the ability to control light in the visible range, but the challenge is getting the ZnO material to infiltrate the structure.

Cross section

To get around the problem, the Chinese team has decided to grow the particles in situ by soaking the sections of peacock feather in a series of reactants. The researchers are confident that the feather's internal and external keratin layers provide functional sites for the formation of ZnO. SEM images taken by the group show a feather covered with particles measuring 8.5–13.5 nm in diameter.

Putting the sample to the test, the ZnO–feather hybrid displays broad emission between 500 and 650 nm when excited at 360 nm. In contrast, the original feather has emission peaks between 400 and 450 nm and, as mentioned earlier, ZnO powder typically displays two emission bands, one at 420 nm and the other at 550 nm.

"The secrets gleaned from nature are a great inspiration for developing functional nanomaterials with hierarchical structures," said Su. "We are in the process of examining other natural biomaterials such as eggshell membrane, silk fibre and butterfly wings, for use in photocatalysis, gas sensing, ductile ceramics and semiconductor technology."