Molecular oxygen sensors based on photoluminescent silica aerogels
Photoluminescent silica aerogel acts as the active element of an optical sensor for molecular oxygen. The luminescent aerogel is prepared by the action of energized reducing gases on a standard silica aerogel. Intensity of aerogel photoluminescence decreases as the collision frequency between oxygen molecules and the luminescent carriers in the aerogel matrix increases. This behavior is a characteristic of many photoluminescent materials and arises from a transfer of energy from the aerogel to surrounding oxygen molecules. A sensor for oxygen concentration or air pressure can therefore be simply constructed utilizing an ultraviolet source for excitation and a suitable detector for the emitted visible signal. Stern-Volmer quenching constants for the aerogel sensing element are 1.55×10-2 Torr-1 for hydrophilic aerogel and 2.4×10-3 Torr-1 for hydrophobic aerogel.