Print this page 19 October 2012 2012/36

Nanoparticles dressed by dark fields boost light emission in a transparent medium

Researchers of the FOM Institute for Atomic and Molecular Physics AMOLF and Philips Research have discovered a material in which they have observed a particular class of light-matter waves (polaritons). Interestingly, this material looks invisible from a distance, even though it strongly interacts with nearby light-emitters. These waves can be applied to improve light emission from LEDs. The results will be published today in the prestigious journal Physical Review Letters.

These waves, known as waveguide-plasmon polaritons, exist in a material formed by an array of small metallic particles (nanoparticles), at a surface that emits light. These nanoparticles strongly scatter the incoming light, because the scale of the array is similar to the wavelength of light. Generally, the scattering of light will make the material opaque, but by coupling the metal particles to the optical waveguide the newly found material becomes transparent.

Also, the resonant interaction between the light emitters in the waveguide increases the emission of light. This is precisely where the advantages for the LED technology comes in. Scientifically, these discoveries introduce a totally new paradigm for enhancing light emission with plasmonic nano optics, because they show that transparent waveguides become more efficient light emitters when they are coupled to nanoparticles.

Reference
S.R.K. Rodriguez, S. Murai, M.A. Verschuuren en J. Gómez Rivas: Light-emitting waveguide-plasmon polaritons, Phys. Rev. Lett. 109, 166803 (2012)
DOI:10.1103/PhysRevLett.109.166803

Further information
For further information, please contact:
Said Rahimzadeh-Kalaleh Rodriguez, (040) 274 30 51
Prof. Jaime Gómez Rivas, (040) 274 23 49

Contact:

Figure 2. Schematic representation of the extinction and the Photo Luminescence enhancement (PLE).

a) Extinction, defining the degree of transparency, and (b) Photo Luminescence enhancement PLE, giving the light emission intensity.Â The black curves correspond to an angle of incidence in (a) and emission in (b) where the two coupled resonances (in the nanoparticles, and in the waveguide) are far apart from each other in energy, or color. The red curves correspond to an angle where the same two resonances coincide in energy, or color. Both plots are shown as function of the photon energy or the color of the light. In a conventional material the extinction is large for the same colors of increased emission. For the waveguide-plasmon polariton, as the red curves show, the emission is maximum at the colors of minimum extinction, i.e., atÂ colors for which the material is transparent.
Figure 1. Schematic representation of the transparent light emitting medium.

(a) multilayer structure formed by a glass substrate (light blue layer), light emitting waveguide (yellow layer), layer of metallic nanoparticles (white dots) and passivation layer (dark grey layer). The blue beam represent the illumination beam used to demonstrate the transparency of the layer. (b) Upper view of the layer of metallic nanoparticles. The scale bar corresponds to 0.0000003 m.