Sensitivity of microstructure fibers to gaseous oxygen

Abstract The paper presents new experimental results related to fluorescence quenching of a transducer, the tris(1,10-phenanthroline)ruthenium(II) chloride hydrate, applied into several types of microstructure fibers (MSFs). Different types of MSFs with a diameter ranging from 125 to 1010 μm coated with a jacket of UV-curable acrylate were prepared. Segments of these MSFs with a minimum length of about 5 cm were used in the experiments. The segments were modified by thin xerogel layers containing the transducer. The layers were prepared from input sols mixed of TEOS or MTES, ethanol, hydrochloric acid, water, and the transducer. The sols were applied onto the walls by passing a column of the sol through the holes. The formed gel layers were dried at 75 °C. Single-capillary fibers (SCFs) modified with the same sensing layers were also prepared for reference measurements. The sensitivity of the sensing MSFs as well as of the SCFs to gaseous mixtures of oxygen and nitrogen was determined in experiments, in which the fibers were excited by a blue LED at about 470 nm and the spectra of the output light were measured in a range of 400–1000 nm for different concentrations of oxygen. Temporal changes of the output power were measured at about 590 nm. On the basis of experimental results one can arrive at a conclusion that there are two different mechanisms of fluorescence quenching in MSFs. For small values of the hole size and thin walls between the holes the fuorescence quenching does not depend on the concentration of oxygen. In contrast to it, for large air holes and large thicknesses of the walls the fluorescence quenching does depend on the concentration of oxygen.