A luminescent lanthanide-titanium oxo cluster of Eu2Ti4(μ2-O)2(μ3-O)4(phen)2(tbza)10·4CH3CN (1, Eu2Ti4-phen-tbza, phen = 1,10-phenanthroline, Htbza = 4-tert-butylbenzoic acid) was prepared through the reaction of phen, Htbza, Eu(Ac)3·xH2O, and Ti(OiPr)4 in acetonitrile. Its overall absolute quantum yield is 65.4% in solid state and 30.2% in CH2Cl2, and the detection limit of 1 for the nitrobenzene (NB) is 10.5 ppb. When the concentration of NB is 40 ppm, the luminescence quenching of 1 can be observed with the naked eye. Time-resolved excited-state decay measurements indicate that the static quenching process is dominated across the NB concentration of 0-9 ppm. The distinguishable shifts in 1H NMR spectra of NB together with 1 confirm the presence of π···π stacking interactions between the organic ligands in 1 and the NB, which plays a key contribution for the quenching of luminescence.