How Light Passes Through Ordered Macroporous Photonic Crystals Immersed in Solvents

Abstract

Understanding light transmission through 3D macroporous photonic crystals is essential for linking their optical characteristics to any application, particularly when immersed in solvents. We examined TiO2 and SnO2 IOs in a series of common solvents to fix existing issues in Bragg-Snell theory and the definition of the photonic crystal unit cell and pore infilling. Using a comprehensive angle-resolved light transmission study coupled to microscopy examination of the IO structure, we demonstrate experimentally and theoretically that low fill factors are caused by porous material infilling all interstitial vacancies of the colloidal opal template, instead of complete filling of most interstitial voids. By also including an optical interference condition for inverse opals with a larger effective refractive index than their substrate, the optical data for macroporous photonic crystals are now consistent with microscopy measurements. This analysis provides an accurate correlation between the true response of a macroporous photonic crystal to tits primary properties including the index contrast with a solvent, infilled structure and the unit cell definition, and the directionality of the photonic band gap. As control in functional porous and ordered photonic materials has broadening to include biosensing and energy storage for example, a comprehensive and consistent description of how light passes through ordered macroporous photonic crystal structures is an important requirement.