The metal-based emission of a series of luminescent europium and terbium complexes incorporating an aromatic chromophore is rendered pH-dependent either through perturbation of the aryl singlet or triplet energy or by modulating the degree of quenching of the lanthanide excited state. Systems exhibiting each of these pathways have been incorporated in thin-film sot gel matrixes and evaluated as pH sensors in static and flow analyses at constant ionic strength. pH-dependent intensity or ratiometric methods, for emission or excitation spectra, have been defined for lanthanide complexes incorporating substituted phenanthridine (pK(a)* from ca. 6.8 to 7.2) or 6-cyanophenanthridine-2-sulfonyl chromophores (pK(a) similar to 7.14 in human serum solution) (lambda (exc) 365 nm, phiH(2)O = 7.2%).