Fluorescence enhancement by chelation of Eu3+ and Tb3+ ions in sol–gels

Chelation of rare-earth (RE) ions is investigated as a means of enhancing the optical properties of RE-doped silica sol–gels. Two chelating agents—2,6-pyridine-dicarboxylic acid (PDC) and 3-pyridinepropionic acid (PPA) and two different synthesis techniques are studied. Eu(PDC) gels exhibit intense 5D0→7F2 fluorescence in the red under UV excitation and long fluorescence lifetimes compared to Eu(PPA) gels and to gels without a chelating agent. This behavior indicates that the PDC molecule remains associated with the Eu after incorporation into the gel. Similar behavior is seen for 5D4→7F5 green fluorescence in Tb(PDC).