Organic dye-doped glasses, viz., platinum octaethylporphyrin incorporated in silica matrices by the sol–gel method, were prepared and their photochemical properties were investigated. The optical sensing of oxygen using these materials is based on the change in the phosphorescence intensity of the oxygen-sensitive dye. This approach allows the development of a photostable, chemically durable optical oxygen sensor with a fast response time (5 s). There was no significant bleaching after 5 months in the absence of light.