Authors
Silica (SiO 2 ) spheres with diameters of 400−850 nm were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of water and ammonia in an alcoholic medium. By grafting −SO 3 - groups on silica surfaces using the silane coupling agent, 2-(4-chlorosulfonylphenyl) ethyltrimethoxysilane, surface charges of the SiO 2 spheres were greatly enhanced. These highly charged, monodisperse SiO 2 particles readily self-assemble into robust, three-dimensionally ordered crystalline colloidal array (CCA) photonic crystals in water suspension. By evaporating water in the CCA, high quality films of close-packed SiO 2 particle−air arrays form with thickness of 25−125 μm. These SiO 2 CCAs and close-packed SiO 2 particle−air arrays diffract light in the near-infrared (NIR) spectral region according to Bragg's law. By altering the particle number density in the CCA dispersions, the diffraction wavelength can be continuously tuned from ∼800 to ∼1800 nm. Additionally, the diffraction prevented light from transmitting through the CCA and the close-packed SiO 2 particle−air array below ∼550 nm spectral region. The CCA photonic crystal materials could be potentially used as tunable NIR optical filters and/or as photonic band gap materials in the UV−visible spectral region.
No takes yet. Share an insight, caveat, or question.
Wang et al. (2003) studied this question.