Macroporous photonic crystal-based vapor detectors created by doctor blade coating

We report the achievement of rapid and reversible vapor detection by using 3D macroporous photonic crystals created by a continuous and scalable bottom-up technology. Capillary condensation of a condensable vapor in the interconnected macropores with ∼74% porosity leads to the increase of the effective refractive index of the diffractive medium, resulting in the redshift of the optical stop bands. The wavelength shift is linearly proportional to the vapor partial pressure for a spectrum of vapors. Optical simulation and theoretical prediction based on Kelvin equation suggest that a liquid film is formed on the walls of the macropores during vapor condensation.