Sol-gel derived sensitive films for ammonia sensors

The sol-gel technology allows the preparation of silica thin films ranging in porosity from dense to highly porous films (50%). Porous silica films can function as a matrix that is able to bind the molecules of pH-sensitive indicators and therefore can be utilized as a sensitive film in construction of intensity based fibre or planar optical sensors for ammonia detection. We report the fabrication and characterization of ammonia sensitive, highly porous silica films deposited on soda-lime glass plates and doped with the bromocresole purple, and bromothymol blue molecules. In this paper we present the influence of the substrate withdrawal speed from sol on a thickness and a refractive index of the undoped silica films, as well as spectral absorbance characteristics of the doped films. An influence of ammonia concentration in air and relative humidity on a transmission of produced sensitive films is also presented.