The novel europium complex acrylato(1,10-phenanthroline)bis(2-thenoyltrifluoroacetonato)europium(III) [Eu(tta)2(aa)(phen)] [Eu-AAPhen; Htta = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, Haa = acrylic acid, phen = 1,10-phenanthroline], which combines the excellent fluorescence properties of [Eu(tta)3(phen)] and the reactivity of acrylic acid with radicals, has been synthesized. Various amounts of this complex (powder) are mixed with nitrile-butadiene rubber (NBR) and peroxide to form uncured composites. These composites are vulcanized to obtain cured Eu-AAPhen/NBR composites. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that the dispersion dimension for the cured composites is far finer than that for the uncured composites. Wide-angle X-ray diffraction (WAXD) experiments show that the crystallinity of Eu-AAPhen in the composite decreases dramatically after the crosslinking process, implying that in-situ reactions (including polymerization and grafting) of Eu-AAPhen initiated by peroxide radicals should take place during the crosslinking of the NBR matrix with peroxide. The dispersion phase of the cured Eu-AAPhen/NBR composite should be composed of nearly nanometer-sized aggregates of poly(Eu-AAPhen) and residual Eu-AAPhen particles with reduced dimensions. The fluorescence properties of the cured composite are much better than those of the uncured one.