Light Scattering Enhancement at the Absorption Edge in Dewetting Droplets of Cyanine Dyes

• Published in: Advanced optical materials 2017-03, Vol.5 (5), p.np-n/a
• Main Authors: Leclaire, Nicolas A., Boudoire, Florent, Hack, Erwin, Brönnimann, Rolf, Nüesch, Frank A., Heier, Jakob
• Format: Article
• Language: English
• Subjects: Absorption; Arrays; cyanine dye; dewetting droplets; Droplets; Dyes; Extinction; Optics; Refractive index; Refractivity; Scattering
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.201600903

Diffraction properties of thin films of dewetted cyanine dye droplets are investigated and related to the complex refractive index. Strong changes in the index of refraction are often found near the absorption edge of organic dyes. Within a small window of droplet morphologies, scattering efficiency is maximized and becomes wavelength‐selective. The origin of the high scattering efficiency is found to be in the enhancement of scattering at the absorption edge of the dye, where anomalous refractive index dispersion occurs. For a comprehensive understanding of the scattering effect, an analytical solution for the diffraction of an array of scatterers is presented. Finite‐difference time‐domain simulations of the extinction properties are performed and good agreements to the experiments are found. These results pave the way to an easy fabrication of new organic‐based optical devices such as refractive index‐based sensors or color selective diffraction gratings. Arrays of sub‐micrometer‐sized cyanine dye droplets are formed on substrates by a dewetting process. Depending on the droplets' dimensions, scattering follows the behavior of one of three different extinction regimes. The new extinction features originate from the enhancement of light scattering at the absorption edge of the dye, where strong variations of the refractive index occur.