Independent control of optical stop-band wavelength and width of colloidal photonic crystals

Practical Preparation of Elastomer-Immobilized Nonclose-Packed Colloidal Photonic Crystal Films with Various Uniform Colors

Colloidal photonic crystals, which are three-dimensional periodic structures of monodisperse submicron-sized particles, are expected to be suitable for novel photonic applications and color materials. In particular, nonclose-packed colloidal photonic crystals immobilized in elastomers exhibit significant potential for use in tunable photonic applications and strain sensors that detect strain based on color change. This paper reports a practical method for preparing elastomer-immobilized nonclose-packed colloidal photonic crystal films with various uniform Bragg reflection colors using one kind of gel-immobilized nonclose-packed colloidal photonic crystal film. The degree of swelling was controlled by the mixing ratio of the precursor solutions, which used a mixture of solutions with high and low affinities for the gel film as the swelling solvent. This facilitated color tuning over a wide range, enabling the facile preparation of elastomer-immobilized nonclose-packed colloidal photonic crystal films with various uniform colors via subsequent photopolymerization. The present preparation method can contribute to the development of practical applications of elastomer-immobilized tunable colloidal photonic crystals and sensors.

The Impacts of Fluorine-Doped Tin Oxide Photonic Crystals on a Cadmium Sulfide-Based Photoelectrode for Improved Solar Energy Conversion under Lower Incidence

Incident angle variation of light from the sun is a critical factor for the practical utilizations of solar energy devices. These devices typically receive the zenith of photon density under a solar elevation angle of 90°, and dramatic deletion of light density along with the decrease of solar elevation angle. Photonic crystals (PCs) with long range ordered arrays possess the controllable position of the photonic stop band (PSB) reliant on several factors, including incident angles, based on the Bragg–Snell law. The multiple scattering, refraction and inhibition of charge carrier recombination within the PSB suggests the potential capability for improving the efficiency of photoactive materials. In this work, we focus on the multiple scattering and refraction effects of PCs. A photoelectrode based on photonic crystal fluorine-doped tin oxide (PC FTO) film was fabricated, which allows the embedded photoactive materials (CdS nanoparticles) to benefit from the features of PCs under variable incidence, especially under lower incidence. The photoelectrode thus has enhanced overall photoelectrochemical (PEC) efficiency in different seasons, even if the increased surface area factor is deducted.