Provided are sensors and methods of measuring the oxygen concentration of a fluid. An excitation light source is in optical communication with a transducer for transmitting an excitation light that is at least partially absorbed by the transducer. The transducer has a property of photoluminescence, and enters a higher energy state by at least partially absorbing the excitation light and enters a lower energy state through radiation of emitted light, thus producing spectral indicia. A light detection system, which is also in optical communication with the transducer, processes the spectral indicia to determine the concentration of oxygen in the fluid.