Abstract: A composite comprises a polymer matrix and a luminophore dispersed therein. The composite is useful as a sensing film that is used as an optical sensor for oxygen measurement comprising the composite sensing film; a source of photons for photo-exciting the luminophores and a waveguide, transparent in the frequency range of the excitation photons, for guiding the excitation photons from the source to the composite sensing film; a detector for measuring properties of photons emitted from the luminophores. A system including a computer may be useful for coordinating the activities of the sensor.