The ability to determine oxygen concentration is of great importance in many industrial, environmental and medical applications. In recent years, a range of sol-gelderived optical oxygen sensors, for measuring oxygen in both gas and aqueous phase has been developed, in which the oxygen sensitive dye Ru(II)-tris(4,7 - diphenyl-1, 10-phenanthroline) has been entrapped. The porosity of the matrix plays a vital role in determining both the sensitivity and response time of such optical sensors. For gas sensors, the diffusion coefficient for the analyte gas through the matrix increases with film porosity. This in turn increases the sensitivity of the sensor response via the Stern-Volmer coefficient. The response and recovery times are also related to porosity via the diffusion coefficient. This project focuses on the fabrication of a wide range of sol-gel-derived thin films as well as the development of experimental systems used to calculate the porosity and response times of a wide range of sol-gel-derived thin films. A method to calculate the diffusion coefficient using response and recovery times as well as film thickness is also detailed. Measured response times were correlated with porosity, Stern-Volmer coefficients and diffusion coefficients data. The Stern-Volmer equation was also used to characterise and explain specific film behavior. A fabrication method used to control the refractive index of sol-gel thin films is also detailed and the consequence this has on the film characteristics is investigated.