Thomas Kotte
When light is incident upon particles with sizes comparable to the wavelength, this light is scattered in different directions. This effect is the reason the sky is blue! The direction of the scattered light is dependent on the geometry and material of the particles. Therefore, it is theoretically possible to design nanoparticles in such a way that the light is scattered into a desired direction. This could potentially be used in many different products: LEDs, diffusers, miniaturized satellites and more.
To understand how the light is scattered by small particles, we first need to realize that light is a form of electromagnetic radiation. This means that light is a combination of oscillating electric and magnetic fields. How fast these field oscillate determines the colour of the light we see. From blue light with the fastest oscillations (for visible light) all the way through the colours of the rainbow to red light where the oscillations are slower. Visible light is not the only form of electromagnetic radiation, for example x-rays or microwave radiation.
What happens when light hits a nanoparticle? The electrons in the material start to move under the influence of the electric and magnetic fields, absorbing some of the light. Because of the movement of the electrons, electromagnetic radiation is created. This is similar to how an antenna works: electrons in the antenna are moved up and down, creating a (electromagnetic) radio signal. In other words: when light hits a nanoparticle, some of the light is absorbed and reemitted by the particle. The amount of and the direction of the light is then dependent on how easily the electrons move (what material the nanoparticle is made of) and in which direction they move (geometry of the particle).
In practice it still proves to be difficult to design nanoparticles to have specific scattering behaviour. The reason for this is that the determination of scattering characteristics relies on time-consuming numerical methods. The aim of this research is to establish design rules for scattering nanoparticles and experimentally confirm them, such that they can be used for the development of new products and technologies.
The result of this research could open up more possibilities in the design of LEDs, improving their efficiency and directionality and diffusers, allowing more control over their properties boosting the quality of optical devices they are incorporated in.