Disorder explains dual‐band reflection spectrum in spherical colloidal photonic supraparticle assemblies

Abstract

Abstract Spherical colloidal photonic supraparticle systems or assemblies (SCAs) are investigated as a model system for confined optical and photonic components. Simulations of the reflection spectrum to calculate their photonic and optical properties for different parameter constellations are compared with experimental studies by microreflectance spectroscopy (μRS) on SCAs fabricated by inkjet in‐flight deposition, proving the existence of a dual‐band reflection spectrum originating from the supraparticle system. Finite‐difference time‐domain (FDTD) calculations are employed to verify these findings as a function of structural parameters. Both, theory and experiment, show a double reflection peak for the SCAs and agree well in the variation of position and shape, scaling clearly with the packing density of the SCAs. Reducing this parameter from 0.6 to 0.3, the higher‐wavelength reflection maximum decreases in intensity and increases in width but keeps its spectral position. The lower‐wavelength reflection maximum decreases in intensity, increases in width and shows a red shift. The results clearly indicate that aspects of disorder decisively contribute to the particular spectral photonic properties of the supraparticle system which are usually related to order in photonic crystals. This finding can stipulate novel, tailor‐made nanostructured optical components such as low‐dimensional micro resonators and waveguides.

Keywords

• colloids
• optical properties
• photonic crystals
• reflection spectroscopy
• self‐assembly