Facile Wet‐Process to Free‐Standing Whispering Gallery Mode Resonators Mixed with Spherical Silica Gel and π‐Conjugated Molecules.

Whispering‐gallery‐mode (WGM) resonators composed of organic and/or inorganic materials have been used in highly sensitive sensors, logic gates, and miniaturized lasers because of the total internal reflection of photons. However, most fabrication methods have been limited to bottom‐up self‐assembly; whereas, a facile top‐down process is preferable. Here, a wet‐process fabrication of WGM resonators mixed with 5 µm‐diameter spherical silica‐gels and various π‐conjugated compounds is demonstrated. The materials are fabricated by dip‐coating photoluminescent molecules onto submicron‐scale silica‐gel spheres. The shapes and large specific surface areas of templates are maintained before and after coating, and the coated molecules are uniformly distributed. The hybrid spheres provided WGM photoluminescence spectra based on the total internal reflection of photoluminescence in the sphere. The hybrid spheres are applicable as WGM sensors because of their large specific surface area (>4 × 102 m2 g−1). In particular, gas sensing of toluene, which has been used as a standard for environmental contamination, and found that the WGM photoluminescence peaks are shifted by 5 nm is demonstrated. The detection resolution is calculated to be several hundred ppm level. The hybrid spheres can be placed or transferred onto various surfaces without micromanipulation, which suggested a wide range of possible applications. [ABSTRACT FROM AUTHOR]